and the items on which the fish feed account for the major interaction
between man and these two groups of animals.
In this paper, we consider how marine birds and fish interact. Although
some of what we present is only speculative, we identify certain areas
that have received little or no scientific study, areas in which
further research is needed for a better understanding of the role of
commercial fish in the ecology and dynamics of marine birds in the
eastern Bering Sea.
Commercial Fish Resources of the Eastern Bering Sea
Most of the fishing in the eastern Bering Sea is done by Japan and the
Soviet Union. Japan resumed fishing in the Bering Sea in 1953 (7 years
after World War II), the Soviet Union started fishing in the region in
1959, and since the early 1960's both nations have accelerated their
exploitation of Bering Sea fish stocks (Chitwood 1969).
Species of major concern to Japan and the Soviet Union include
fish--walleye pollock _(Theragra chalcogramma)_, yellowfin sole
_(Limanda aspera)_, Pacific cod _(Gadus macrocephalus)_, Pacific ocean
perch _(Sebastes alutus)_, Pacific herring _(Clupea harengus pallasi)_,
and sablefish _(Anoplopoma fimbria)_--and snow crabs (_Chionoecetes_
spp.). The distribution of the principal species being harvested in
Bristol Bay and the eastern Bering Sea are shown in Figs. 1, 2, and
3. The weight of each of the major species in the total catches made
by foreign and domestic fishermen in 1973 is shown in Table 1. In
1972, the catch of commercial finfish in the eastern Bering Sea alone
amounted to 5% of the total world catch of marine fishes (H. Larkins,
personal communication).
Most species of commercial fish in the Bering Sea are in a state of
decline or in a depressed condition from overexploitation (Table 1).
This is indicated by a reduction in the catch per unit of effort and
in the mean size of fish in the commercial catch (H. Larkins, personal
communication). The notable exception is the king crab (_Paralithodes_
sp.), which has increased in abundance in recent years as a result of
reduced foreign fishing.
Table 1. _Foreign and domestic catch of fish and shellfish in the
eastern Bering Sea, including Bristol Bay, 1973._
----------------------------------------------
Catch
Species (metric tons)
----------------------------------------------
Fish
Pollock 1,500,000
Flatfish 125,000
Pacific cod 45,000
Herring 35,033
Salmon 11,785
Sablefish 7,000
Pacific halibut 222
Other 40,000
Shellfish
King crabs 26,798
Snow crabs 17,694
Shrimp Minor
----------------------------------------------
[Illustration: =Fig. 1.= Areas of major concentrations of ground fish
(Pacific pollock, halibut, yellowfin sole, rock sole, flathead sole,
Pacific ocean perch, and Pacific cod) in Bristol Bay and the Bering
Sea.]
[Illustration: =Fig. 2.= Areas of major winter and spring
concentrations of Pacific herring in Bristol Bay and the Bering Sea.]
[Illustration: =Fig. 3.= Areas of major concentrations of king and snow
crab in Bristol Bay and the Bering Sea.]
Routes of Interaction Between Marine Birds and Commercial Fish
The obvious ways in which marine birds and fish of commercial
importance interact in the eastern Bering Sea are illustrated by the
simplified food web diagram in Fig. 4. The major animal groups and
species included in two of the categories in this figure--secondary
producers (invertebrate forage) and intermediate carnivores (commercial
and forage marine fish and shellfish)--are as follows:
_Secondary producers_
Zooplankton and micronekton
Copepods
_Calanus_ spp.
_Eucalanus_ spp.
Euphausiids
_Thysanoessa_ spp.
Amphipods
_Parathemisto_ spp.
_Gammarus_ spp.
Pteropods
_Spiratella_ spp.
_Clione_ spp.
Chaetognaths
_Sagitta_ spp.
Benthos
Polychaetes
_Nereis_ spp.
_Euroe_ spp.
Molluscs
_Mytilus edulis_
_Tonicella_ spp.
_Fusitriton oregonensis_
Echinodermata
_Strongylocentrotus_ spp.
Crustacea
Gammaridae
Mysidae
_Idothea_ spp.
_Pagurus_ spp.
_Hapalogaster_ spp.
_Sclerocrangon_ spp.
_Intermediate carnivores_
Eggs (littoral, adhesive)
Clupeidae
Pelagic larvae
Gadidae
Pleuronectidae
Osmeridae
Ammodytidae
Salmonidae
Gadidae
Pandalidae
Juvenile and small adults
Clupeidae
Osmeridae
Ammodytidae
Salmonidae
Gadidae
Pandalidae
Large adults
Clupeidae
Gadidae
Pleuronectidae
Salmonidae
Scorpaenidae
Lithodidae
Majidae
Pandalidae
Marine birds
Alcidae
Procellariidae
Laridae
Phalacrocoracidae
[Illustration: Fig. 4. Food web in the eastern Bering Sea, showing
routes of interaction between marine birds and the various life history
stages of commercial fish and shellfish.]
In our discussion, we mainly consider predation by birds on commercial
fish and competition between birds and commercial fish for food.
The extent of these interactions determines the potential for birds
and fish to influence each other's abundance. The extent of the
interactions also determines the impact of man's commercial harvest
of fish on the abundance of birds or of the bird's harvest on the
abundance of fish.
The extent of the interaction between marine birds and commercial
fish depends on the abundance, distribution, feeding habits, and life
history of the fish species of concern. We have limited our discussion
to examples of the major commercial pelagic and demersal fish and
shellfish of the eastern Bering Sea. We also use as examples those
species of marine birds whose abundance in the eastern Bering Sea and
feeding habits give them the greatest potential for influence on, or
being influenced by, fish abundance.
Abundance and Feeding Habits of Marine Birds in the Eastern Bering Sea
Information on the general abundance and distribution of the most
important marine birds in the eastern Bering Sea in the summer and
winter is scattered among many published and unpublished reports:
Shuntov (1961, 1966), Sanger (1972), Bartonek and Gibson (1972), and
Ogi and Tsujita (1973); and surveys by D. T. Montgomery and W. E. Oien
("Bristol Bay waterbird survey, 1972," unpublished report of the U.S.
Bureau of Sport Fisheries and Wildlife, Alaska area) and by J. G.
King and D. E. McKnight (1969, "A waterbird survey in Bristol Bay and
proposals for future studies," unpublished report of the U.S. Bureau
of Sport Fisheries and Wildlife and the Alaska Department of Fish and
Game, Juneau, Alaska).
In summer, the most abundant birds appear to be the procellariids,
mainly the slender-billed shearwater _(Puffinus tenuirostris)_ and
Pacific fulmar _(Fulmarus glacialis)_; the alcids, mainly the common
murre _(Uria aalge)_, thick-billed murre _(U. lomvia)_, tufted puffin
_(Lunda cirrhata)_, horned puffin _(Fratercula corniculata)_, and the
ancient murrelet _(Synthliboramphus antiquus)_; and the larids, mainly
the glaucous-winged gull _(Larus glaucescens)_ and the black-legged
kittiwake _(Rissa tridactyla)_.
In winter, the alcids and larids appear to be the most abundant
groups, the procellariids having been reduced by the departure of
the slender-billed shearwaters for breeding grounds in the southern
hemisphere. The selection of the types of food to be consumed by these
marine birds is a function of their morphological and physiological
adaptations and of the resultant feeding behavior. Ashmole (1971)
classified the feeding behavior of various genera of marine birds and
the relative importance of the kinds of food eaten by each group; this
information for some of the Bering Sea bird species occurring in the
genera listed by Ashmole (1971) is summarized in Fig. 5.
Fish and invertebrates are evidently of moderate to major importance in
the diet of these marine birds (Fig. 5). The extent to which a given
fish species is fed upon by or is in competition with marine birds
for food is determined by the life history of the fish. Most pelagic
and some demersal fish and shellfish are more subject to predation
by pursuit diving birds than by birds restricted to the near-surface
waters. Invertebrates appear to be equal to or more important than fish
in the diets of birds feeding in near-surface waters (Fig. 5).
Predation by Marine Birds
The literature contains numerous accounts of marine birds feeding
on marine fish and shellfish of commercial importance. Some studies
quantify the impact of some bird species on certain species of
commercial fish (Outram 1958; Shaefer 1970; Wiens and Scott 1976) and
shellfish (Glude 1967). Other studies have shown that in some regions
the value of guano produced by birds may exceed the value of the
commercial fish they consume (Jarvis 1970). Some fish of worldwide
commercial importance that are important in the diets of marine birds
are listed in Table 2.
Table 2. _Fish of worldwide commercial importance in the diets of
some marine birds._
--------------------------------------------------------
Fish Shearwaters Murres Puffins Fulmars Gulls
Anchovy X -- -- -- --
Sardines X -- -- -- --
Herring X X X X X
Sprat X -- -- -- --
Pilchard X -- -- -- --
Capelin -- X X -- X
Salmon -- X -- -- --
Mackerel -- X -- -- --
Pollock -- X -- X --
Haddock -- X -- -- --
Cod -- X -- -- --
--------------------------------------------------------
The significance of bird predation on pelagic or demersal fish and
shellfish (Fig. 5) depends on the feeding behavior of the birds and on
the life history of the fish (e.g., distribution, abundance, growth,
and adult size). Pursuit diving birds, such as murres and puffins,
can consume fish at greater depths than can birds that feed near the
surface, such as shearwaters, kittiwakes, fulmars, and gulls.
[Illustration: Fig. 5. Feeding behavior and relative importance of food
of some groups of marine birds that occur in the eastern Bering Sea.]
Aspects of the Life Histories of Fish Related to Predation by Marine
Birds
Fish that are pelagic during part of their lives, such as salmon and
herring, and forage fish like smelt, capelin, and sand lance, are
vulnerable to greater predation by a wider variety of marine birds than
are bottom-dwelling demersal fish, such as pollock, cod, sole, ocean
perch, and halibut, as well as king and snow crabs. Some species that
live on the bottom as adults have pelagic stages during which they are
vulnerable to predation by marine birds. Juveniles of some demersal
species (pollock, cod, halibut, some species of sole, and king crabs)
are sometimes found in shallow water where they might be subject to
predation by birds.
_Demersal Fish and Shellfish_
The early life histories of the commercially important demersal fish
of the eastern Bering Sea are quite different (Table 3). For example,
the eggs and larvae of Pacific halibut _(Hippoglossus stenolepis)_
generally occur at depths greater than 100 m (Hart 1973), whereas
those of pollock and yellowfin sole are found at or near the surface
(Musienko 1963, 1970). The eggs of Pacific cod are demersal, but the
larvae are oceanic (pelagic) and occur from 25-150 m (Mukhacheva and
Zviagina 1960).
In their juvenile stages, many demersal fish frequent the near-surface
waters (Table 3), where they become vulnerable to predation by
piscivorous marine birds. Juvenile pollock, for example, form into
small schools that usually move about close to the bottom but sometimes
move into areas as shallow as 3 m. Juvenile Pacific cod prefer the
warmer water close to shore and may be found within 10 m of the
surface (Moiseev 1953). The young of many species of flatfish, such as
yellowfin sole, rock sole _(Lepidopsetta bilineata)_, and flathead sole
_(Hippoglosoides elassodon)_, remain for a time in shallow warm water
after assuming a demersal existence. Yellowfin sole 2-2.5 cm in total
length may be found in abundance in areas as shallow as 5 m (Fadeev
1965; Moiseev 1953).
Table 3. _Informal listing of life history information on
selected species of commercial and forage fish and shellfish to
show vulnerability to predation by marine birds._ (? indicates no
information available.)
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Yusa 1954
(cm)[54] Tanino et al. 1959
=Walleye pollock= 31-35 95,700 Feb.- April Kobayashi 1963
(_Theragra_ 46-50 324,400 June -May Musienko 1963, 1970
_chalcogramma_ Serobaba 1968
Pallas) Hart 1973[55]
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 0.1-0.2 0-10 Feb.-June { 12 at 6-7°C
{ 20.5 at 3.4°C[57]
Larval 0.4-0.9 10-25 March-? > 25 at 6-7°C
Larval 0.9-? 25-? ?-Sept. ?
Juvenile 2.2-4.1 0-?[58] Summer --
Juvenile 6.0-30.0 4-37 Summer --
Adult 30.0-70.0 0-386 -- --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Moiseev 1953
(cm)[54] Mukhacheva and
=Pacific cod= 60 1,200,000 Jan.- ? Zviagina 1960
(_Gadus_ 78 3,300,000 March Musienko 1970;
_macrocephalus_ Hart 1973[55]
Tilesius)
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 0.1-0.11 100-250 Demersal { 8-9 at 11°C
{ 17 at 5°C
{ 28 at 2°C
Larval 0.5-3.2 25-150 Feb.-Aug. ?
Juvenile ? 10-? Summer --
Adult 40.0-99.0 0-900 -- --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Stevenson 1962
(cm)[54] Musienko 1970
=Pacific herring= 20.5-22.0 26,600 May- Varies Rumyantsev and
(_Clupea_ 28.0-31.0 77,800 June Darda 1970
_harengus pallasi_ Reid 1972
Valenciennes) Hart 1973[55]
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 0.1-0.2 0-12 Demersal 10-20[57]
Larval 0.9 0.5-8 May-June }
Larval 1.3 0.5-8 June-July } 42-56
Larval 2.5 1-6 July-Aug. }
Juvenile 2.5-20.5 0-? March-Nov. --
Adult 20.5-31.0 0-140 March-Nov. --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period
(cm)[54] Clemens and
=Capelin= ? 3,000 June- ? Wilby 1961
(_Mallotus_ ? 6,000 July Musienko 1970
_villosus_ 10.3 6,670 Hart 1973
(Muller)) ? 60,000
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 0.1 <20 Demersal 14-?
Larval 0.5-? ? June-? ?
Juvenile ? ? March-Nov.(est.) --
Adult ? 0-? March-Nov. --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Musienko 1963, 1970
(cm)[54] Kashkina 1970
=Pacific sand lance= -- ? June- [59] Hart 1973
(_Ammodytes_ Aug.
_hexapterus_ Pallas)
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg ? ? Demersal ?
Larval 0.7-3.4 0-? June-Sept. ?
Juvenile 3.6-9.6 0-? ? --
Adult 26 0-? ? --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Paraketsov 1963
(cm)[54] Lisovenko 1965
=Pacific ocean perch= 26 10,000 March- ? Lyubimova 1965
(_Sebastes_ 44 180,000 May Kashkina 1970[60]
_alutus_ (Gilbert))
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg[61] -- -- -- --
Larval[62] 0.6-? [62] March-Aug. ?
Juvenile 6.2 37-128 -- --
Juvenile 10.4 37-154 -- --
Juvenile 14.7-21.3 37-230 -- --
Adult 21.3-51.0 37-420 -- --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period
(cm)[54] Novikov 1964
=Pacific halibut= 75 101,723 Oct.- ? Hart 1973
(_Hippoglossus_ 135 2,800,837 March
_stenolepis_
Schmidt) Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 0.3-0.4 40-935 Oct.-March 48 at ?
Larval 0.8-1.5 >200 Nov.-May }
Larval 1.5-2.9 <100 May-Sept.} 70-98
Juvenile 3.4-4.2 7-43 -- --
Juvenile 19-25 7-45 -- --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Moiseev 1953
(cm)[54] Pertseva-Ostraumova
=Yellowfin sole= 1954; Musienko 1963;
(_Limanda_ 26.1-28.0 1,295,000 June- July Fadeev 1965;
_aspera_ 40.1-42.0 3,319,500 Aug. Kashkina 1965_a_,
(Pallas)) 1965_b_[55]
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 0.07-0.09 >0 June-Aug. 9.4 at 13.1°C[57]
Larval 0.2-1.2 >0 July-Oct. ?
Juvenile 2.1-2.5 5-15 -- --
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period
(cm)[54] Kurata 1960, 1964
=King crabs= 9.4 55,408 April- ? Korolev 1964
(_Paralithodes_ 17.1 444,651 June Rodin 1970
_camtschatica_ (Tilesius))
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg -- 100-200[63] -- ?
Zoeal} 0.55-0.65 ? April-July {33 at 7-10°C
Zoeal} {23 at 12.3-12.5°C
Glaucothoeal 0.38x0.18 ? May-? ?
Juvenile ? 1-? -- ?
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Haynes 1973[55]
(cm)[54] Jewett and
=Snow crabs= Haight[64]
(_Chionoecetes_ ? ? ?[65] ?
_bairdi_ Rathbun)
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg 100[63] -- ?
Prezoeal 0.22-0.28 ? May-? 1-2 at 2.5°C
1st zoeal 0.50-0.56 ? Summer ?
2d zoeal ? 0-10 Summer ?
Megalopal 0.30-0.35x ? Summer --
0.18-0.21
Juvenile 0.44-0.48x ? -- --
0.32-0.35
Fecundity Spawning season Source of data
Length Mean no. Total Peak
of female of eggs period period Ito 1968; Kon 1970
(cm)[54] Haynes 1973;
=Snow crabs= Motoh 1973
(_Chionoecetes_ ? ? ?[65] ? Jewett and
_opilio_ Haight[64]
(O. Fabricius))
Total Depth from Seasonal Duration of
Life length surface period of life stages
stage (cm)[56] (m) pelagic life (days)
Egg ? 93[60] -- ?
Prezoeal -- ? May-? }
1st zoeal 0.48-0.54 ? Summer }
2d zoeal 0.62-0.71 ? Summer } 63-66 at 11-13°C
Megalopal 0.29-0.33 ? Summer }
0.19
Juvenile 4.4-4.8x ? -- --
3.2-3.5
The commercially important king and snow crabs of the eastern Bering
Sea also have larval stages that are pelagic (Table 3). Zoeae and
megalopa of snow crabs are found near the surface where they are
vulnerable to plankton-feeding marine birds. The eggs of king crabs are
attached to the abdomen of the female, but after hatching, the larvae
become pelagic and occur near the surface. They are planktonic through
five larval stages before settling to the bottom to take up demersal
residence (Kurata 1960, 1964). These larvae attain a length of 5.5-6.5
mm and spend 33 days or more in the plankton (Kurata 1960). Even
after the young king crabs have settled to the bottom, they may still
frequent water shallow enough to make them vulnerable to predation by
some marine birds. Juvenile king crabs 1 and 2 years of age appear to
prefer shallower water than do older crabs. In southeastern Alaska,
during the spring, small juvenile crabs have been observed in pods at
depths as little as 1 m below the low tide level.
The available life stages of king and snow crabs and commercially
important demersal fish (Table 3) represent an enormous food supply for
other fishes and marine birds. Predation by marine birds on pelagic
eggs and on the larval and juvenile stages of demersal fish is not well
documented, probably because the rapid digestion rate of birds makes
species identification of these stages difficult. Investigators must
often depend on the presence of the hard parts of fish (such as scales
and otoliths) in the stomachs of birds to identify the species eaten.
Because these hard parts have not yet formed in the larvae and most
juveniles, predation by marine birds on older fish is more apparent on
examination of stomach contents. Full understanding of predation by
marine birds on demersal fish and shellfish requires additional data on
when and where the egg, larval, and juvenile stages are present.
_Pelagic Fish_
Many fish, such as herring, capelin, smelt, and salmon, are pelagic
for part of their lives, particularly during the spring and summer
feeding periods. The extent of predation by marine birds on these
species depends primarily on the location of their spawning grounds,
their growth rates, and the size of the adults. The spawning location
determines the extent of predation on eggs, whereas growth rate and
adult size determine during how much of its lifetime a given fish
species is vulnerable to the wide variety of marine birds.
Herring spawn in intertidal and subtidal zones and spend most of
their post-larval lives in bays or estuaries near the coast. They
deposit their adhesive eggs primarily on vegetation, and the eggs are
particularly vulnerable to predation by a wide variety of marine and
terrestrial birds. Outram (1958) estimated that gulls alone accounted
for 39% of the egg loss on the spawning grounds at Vancouver Island,
British Columbia. When herring larvae hatch, they are between 0.7 and
0.8 cm long; when they metamorphose about 6-8 weeks later, they are
between 2.6 and 3.5 cm long. Thereafter, juvenile herring grow rapidly
and reach a length of about 7-10 cm before winter. Although herring
as old as 13 years and up to 38 cm long have been reported in Alaska,
they seldom exceed 30 cm and 11 years of age (Rounsefell 1929). During
spring and summer, herring are commonly within 10 m of the surface,
but in winter, they are in water 100-140 m deep. Although herring are
particularly vulnerable to predation in spring and summer, they are
available to marine birds during most of their life.
The life history of capelin is somewhat different than that of
herring--they live in the open sea near the surface and throughout the
water column most of their lives. Sometime in June or early July, they
migrate in large schools toward shore to spawn (Musienko 1970). In
British Columbia, capelin bury their eggs in coarse sand and gravel in
the intertidal and subtidal zones. The larvae are 0.5-0.7 cm long at
hatching and are carried by currents to the open sea where they develop
in the plankton. Capelin attain an age of 5 years and a maximum length
of about 22 cm; their small size makes them vulnerable to predation by
marine birds most of their lives, and they are an important pelagic
food fish for other commercial fish in the Bering Sea.
The sand lance reaches a maximum size of 20-26 cm and is vulnerable to
bird predation during most of its life. Little information is available
on the maximum age attained by this species in the Bering Sea, but
because of its size, it is an important forage fish for many commercial
fish species.
The five species of Pacific salmon of the eastern Bering Sea spawn
in fresh water, unlike herring, capelin, and sand lance. Their eggs
are not vulnerable to extensive predation by marine birds; gulls take
mainly salmon eggs which have been dislodged from the gravel and are
drifting or being rolled along the stream bottom by the current (Moyle
1966). After a few months to several years in fresh water, the juvenile
salmon (5-14 cm long) enter the Bering Sea during late spring or early
summer and migrate through these waters to feeding grounds, primarily
in the north Pacific Ocean. At maturity, the survivors return to their
home streams and rivers to spawn. It is during the seaward migratory
phase of their life cycle that salmon are most vulnerable to predation
by marine birds.
The sockeye salmon _(Oncorhynchus nerka)_ is the most abundant and
valuable species harvested by American fishermen in the waters adjacent
to the Bering Sea and, as a result, the one that has been most
extensively studied during early marine life. Juvenile sockeye salmon
are between 8 and 14 cm long when they enter the Bering Sea between
late May and early July. They are most abundant in the upper 1 m of
water at night and the upper 2 m during the day (Straty 1974)--well
within the regime that can be exploited by many species of marine birds.
The numbers of juvenile sockeye salmon migrating seaward from the
Bristol Bay region of the Bering Sea in a single year has ranged
between 46.3 and 370.4 million (H. Jaenicke, personal communication).
This is equivalent to between 409 and 3,267 metric tons (on the basis
of the mean weight of the juveniles when they enter the Bering Sea).
These large numbers of juvenile sockeye salmon, plus juvenile chinook
salmon _(O. tshawytscha)_, coho salmon _(O. kisutch)_, chum salmon _(O.
keta)_, and pink salmon _(O. gorbuscha)_ from all other rivers entering
the Bering Sea, represent a considerable input of energy from fresh
water in the form of prime forage fish for other fishes, marine birds,
and mammals. Young salmon enter the Bering Sea each year over a period
of only 6 to 8 weeks and may follow rather discrete coastal migration
routes through the Bering Sea (Fig. 6), with the result that predators
have access to an abundant but transient food supply.
[Illustration: Fig. 6. Distribution of juvenile sockeye salmon in
Bristol Bay and the eastern Bering Sea (adapted from Straty 1974).]
The only published account of predation by marine birds on juvenile
salmon in the Bering Sea is that of Ogi and Tsujita (1973). They found
juvenile sockeye salmon in the stomachs of murres captured in gill nets
in the eastern Bering Sea. The predation did not appear extensive, but
most of the birds were captured outside or on the fringes of the main
seaward migration route of the salmon. The foods of marine birds should
be studied in conjunction with studies of the migrations of juvenile
salmon.
Influence of Growth Rate and Adult Size of Fish on the Extent of
Predation
Incubation time for fish eggs, the length of the pelagic larval period
(Table 3), and the growth rate of juvenile fish are species-specific
and temperature-dependent. The extent to which a fish species is
subjected to predation by marine birds is directly related to the rate
at which development and growth occur. For example, the less time it
takes the pelagic eggs of demersal fish and shellfish to hatch and
complete pelagic larval life, the less is the time they will be preyed
on by marine birds. For fish species that are pelagic during their
entire life, the rate of growth will determine how long they remain
small enough for birds to eat. Some of the smaller pelagic fish, such
as herring, capelin, and smelt, are vulnerable to bird predation most
of their lives; larger pelagic species like salmon may be preyed on
for only a very short time. The maximum size fish that can be eaten
by marine birds is, therefore, important in evaluating predation on a
given species of fish.
The literature on the food habits of marine birds contains little on
the sizes of fish consumed. Tuck (1960) stated that murres probably
will take fish up to 18 cm long. Ogi and Tsujita (1973) estimated the
lengths of Pacific pollock in the stomachs of murres taken in the
eastern Bering Sea at 24 cm.
Herring in the eastern Bering Sea reach an age of 11 years and grow to
about 33 cm. Herring could, therefore, be taken during most of their
lives by murres but during only the first few years by smaller birds
such as fulmars and shearwaters. Capelin and some species of smelt
would be vulnerable to birds during all their lives. Although the size
of adult Pacific salmon varies with the species, they are all so large
that they are not preyed upon by marine birds. Once in the ocean,
juvenile salmon grow at such a rapid rate that they are probably not
very vulnerable to marine birds after their first 4 to 6 months at sea.
Limited studies on the growth of juvenile sockeye salmon in the eastern
Bering Sea (Straty 1974) indicate they may double their size in their
first 8 weeks at sea. A sockeye salmon that entered the Bering Sea at
12 cm in mid-June would be 24 cm long in August--the maximum size that
a murre could eat; the fish could be eaten by smaller marine birds for
much less time. Pink and chum salmon enter the sea at a smaller size
than sockeye salmon and would be vulnerable to predation both by a
greater variety of marine birds and for a longer period of time.
Competition Between Commercial Fish and Marine Birds
We do not know the importance of competition between marine birds and
commercial fish in the eastern Bering Sea. Only a few investigators
have even alluded to competition between marine birds and fish for
food. Ogi and Tsujita (1973) mentioned that competition seemed to exist
between murres and juvenile sockeye salmon for euphausiids in the
eastern Bering Sea. We have listed some of the types of forage fish
and invertebrates eaten by commercial fish (Table 4) and marine birds
(Table 5) in the eastern Bering Sea; comparison of these two tables
clearly indicates that competition could occur.
The principal factors determining the extent of competition between
marine birds and fish are the numbers of birds and fish, the length of
time that various life history stages of the fish are in association
with the birds, and the abundance of the preferred foods at these
times. The impact of competition depends on the adaptability of the
birds and fish to alternative types of food.
The types and sizes of food eaten by fish vary with the life history
stage--especially with size at each stage. For instance, very young
herring eat the eggs and nauplii of copepods or small copepodite stages
and barnacles. As herring grow, their diet includes small fish and
larger zooplankton, such as mature copepods, amphipods, euphausiids,
and pteropods. Pacific cod shorter than 9 cm feed on small crustaceans
(Moiseev 1953), whereas larger cod eat young crabs, shrimp, and
fish. Small juvenile sockeye salmon feed mainly on larval stages of
euphausiids (Straty 1974), but larger juveniles also eat the more
adult forms, which eventually make up a significant part of their diet
(Nishiyama 1974).
The change in the diet of fishes with growth results in competition
with a changing variety of marine birds. For example, deep-diving
birds may replace surface feeders as the major bird competitors of the
Pacific cod and pollock as these fish increase in size and seek deeper
waters. The diet of cod changes from small crustaceans in shallow water
to progressively larger food that eventually includes herring, sand
lance, shrimp, and crabs. The change to herring and sand lance, and
quite possibly small crabs, places the adult cod in competition with
both the surface feeders and pursuit diving birds, but adult cod do not
compete with birds for zooplankton.
Table 4. _Food items eaten by the adult stage of seven
commercially important species of fish in the eastern Bering Sea._
Pacific
Food Walleye Pacific ocean Yellowfin Pacific
item Herring Salmon pollock cod perch sole halibut
Invertebrates
Pteropods X X -- -- X -- --
Squid -- X -- X X -- X
Polychaetes X X X X -- X X
Copepods X X X -- -- -- --
Amphipods X X X X X X --
Euphausiids X X X -- X X --
Decapods X X X X X X X
Fish
Capelin X X X X -- X --
Sand lance -- X X X -- -- X
Table 5. _Forage fish and invertebrate foods eaten by seven
species of marine birds in the eastern Bering Sea._
Shear-
Food item waters Murres Puffins Murrelets Fulmars Kittiwakes Gulls
Forage fish
Sand lance X X X -- -- X X
Capelin -- -- X -- -- -- --
Invertebrates
Copepods -- -- -- -- -- X --
Euphausiids X X -- -- -- X --
Amphipods X X -- -- -- X --
Decapods X X -- -- -- X --
Pteropods -- X -- -- -- -- --
Chaetognaths -- -- -- -- -- -- --
Polychaetes -- X X -- -- X --
Squid X X -- -- X -- --
As pollock increase in size, they continue to feed mainly on
zooplankton, but they change from copepods near the surface to
euphausiids at mid-depths and near the bottom. Euphausiids are large
and abundant zooplankters which, for the most part, are available only
to deep-diving birds. Adult pollock also consume herring, sand lance,
capelin, and other small fish.
Both marine birds and fish are capable of exploiting a wide variety of
food, and often their stomach contents reflect the relative abundance
of food items in the area. Ogi and Tsujita (1973) illustrated the
differences in the food taken by murres captured at different locations
in the eastern Bering Sea. Carlson (1977) and Ogi and Tsujita (1973)
reported on differences in the diet of juvenile sockeye salmon captured
at various locations in Bristol Bay and the eastern Bering Sea. The
diets of many species of birds and fish, however, seem to be largely
determined by their physiological and morphological adaptations and
resultant feeding behavior. For instance, adult sockeye and pink salmon
have well-developed gill rakers and feed largely on zooplankton,
whereas chinook and coho salmon have poorly developed gill rakers
and feed almost entirely on fish. In the eastern Bering Sea, murres
appear to prefer the Pacific sand lance, whereas the slender-billed
shearwater consumes mainly euphausiids (Ogi and Tsujita 1973). Thus,
murres may be greater competitors with piscivorous fish than are
shearwaters. Shearwaters are probably more important as competitors
with zooplankton-eating fish that inhabit shallow water in juvenile
stages and with pelagic fish species (such as pollock, herring, salmon,
and capelin) that are heavily dependent on euphausiids.
Some species of marine birds may interact with fish as predators and
competitors. As an example, pursuit diving birds, such as murres
and puffins, may be important predators on juvenile salmon in the
eastern Bering Sea, but these same birds may compete for food with
adult salmon. Surface-feeding birds, such as fulmars, shearwaters,
kittiwakes, and gulls, may be important as both predators and
competitors with herring and capelin and some demersal fish.
Dependency of Marine Birds on Commercial Fish
The interactions of commercial fish and marine birds of the Bering Sea
can be determined only if we know their distribution, abundance, and
food habits, especially while they are associated with one another.
Information is particularly lacking for all life history stages of
commercial fish species and the seasonal movements of birds. We have
some knowledge of the distribution and abundance of the various life
history stages and the food habits of commercial fish in the Bering
Sea. Little is known of the abundance, seasonal movements, and food
habits of marine birds in this region, however, probably because
marine birds have had little direct commercial value in the northern
hemisphere. Food studies on marine birds are particularly difficult
because their rapid digestion soon destroys the identity of the food.
We can make a reasonable guess as to some bird-fish associations
for two regions of the Bering Sea where we have information on the
distribution of marine birds and the various life history stages of
commercial fish. For example, piscivorous birds, such as murres,
puffins, black-legged kittiwakes, and slender-billed shearwaters, are
extremely abundant in the summer along the seaward migration route of
juvenile sockeye salmon (Fig. 7); the juvenile salmon, kittiwakes,
and shearwaters all feed on plankton. Shuntov (1961) showed that
kittiwakes are most abundant along the edge of the continental shelf
in the Bering Sea in the summertime. This distribution coincides
with the distribution of the eggs and larvae of pollock, certain
flatfish, rockfish, sablefish, and several other species. These birds
both exploit the fish directly (predation) and compete with them for
plankton. Not enough information is available on the food habits of
birds at the time fish eggs and larvae are present to evaluate this
interaction.
Environmental Influence on Predation and Competition Between Marine
Birds and Commercial Fish
Because fish are cold-blooded animals, temperature, through its
influence on the rate of metabolism, is a major variable in determining
the amount of energy needed for maintenance and for performing such
essential activities as swimming and feeding--fish are less active,
feed less, and grow more slowly in cold waters. For example, growth
in young sockeye salmon is very slow at temperatures lower than 4°C
(Donaldson and Foster 1941), and temperature profoundly affects their
swimming speed (Brett et al. 1958). The rates of development of the
eggs of some flatfish are closely correlated with water temperature
(Ketchen 1956)--flatfish developed more rapidly at higher temperatures
(Fig. 8). At lower temperatures, the rate of growth is also slower and,
therefore, the duration of pelagic larval life is longer for demersal
fish and shellfish.
Variations in sea temperature should, therefore, influence the extent
to which fish are vulnerable to predation and competition. For example,
eggs would take a longer time to hatch in colder than in warmer sea
water. In both pelagic fish such as herring, whose eggs are laid in
the intertidal zone, and in demersal fish with pelagic eggs such as
the sole, the period of vulnerability of eggs to bird predation would
be extended. At lower temperatures the length of the pelagic life
of demersal fish and shellfish and their vulnerability to predation
would also be greater than at higher temperatures. For example, the
number of days between molts of the zoeal stages of snow crabs is
temperature-dependent--the warmer the water, the less the time between
molts (Kon 1970).
[Illustration: Fig. 7. Distribution and numbers of birds observed in
Bristol Bay along seaward migration route of sockeye salmon (from
Bartonek and Gibson 1972).]
Temperature, through its effects on swimming speed, feeding activity,
and growth of juvenile fish, might influence the magnitude of
predation by birds on pelagic fish in the following ways: (1) lower
sea temperatures would increase the vulnerability of juvenile fish to
bird predation because swimming speed would decrease, and the time the
fish are of a size that could be eaten by would-be predators would
increase; (2) lower sea temperatures would reduce the feeding by fish
and decrease the competition by fish for food exploited by birds; and
(3) higher sea temperatures would have the opposite effect--the feeding
by fish would increase consumption of the foods that birds feed on.
In the eastern Bering Sea, water temperatures may vary greatly between
years for the same month (Fig. 9). Such variation should result in
variation in the temperature-dependent activities of fish and, in
turn, in magnitude of marine bird predation and competition.
[Illustration: Fig. 8. The relation of temperature to the rate of
development to hatching of lemon sole, as compared with two European
flatfishes (Ketchen 1956).]
Possible Influences of Man on the Interaction of Marine Birds with
Commercial Fish
We have noted that the abundance and age and size composition of major
stocks of fish in the Bering Sea have been drastically reduced by
commercial fishing. This has resulted in the reduction in numbers of
fish at all life history stages, including those on which marine birds
and other fishes depend for food. What effect this reduction has had
on the abundance and distribution of marine birds in the Bering Sea is
unknown. It depends in part on the ability of birds to eat other fish
or increase their use of zooplankton or nekton.
We can hypothesize on probable changes in bird and fish abundance that
resulted from the heavy commercial harvest of fish but any such changes
cannot be documented or quantified. A reduction in stocks of a fish
species could result in a reduced supply of food for a species of bird
and cause a shift in the diet of this bird to other species of fish or
to more zooplankton. For a bird species with specific food preferences,
this could mean a reduction in its abundance to a level supportable by
the available food supply. For bird species with less specific food
requirements, a reduction in a species of fish could mean a reduction
in competition for food with that fish--which could increase survival
of the birds.
Man's intentional harvest of marine birds, such as the shearwater in
parts of the southern hemisphere, and his inadvertent harvest of other
bird species which are entangled or caught in fishing gear reduce
predation and competition by marine birds. This, in turn, may aid the
survival of the fish stocks in the Bering Sea.
The status of most stocks of commercial fish and shellfish in the
Bering Sea is such that reductions in harvest are warranted, have
been proposed, or are in effect. If the 200-mile (61-km) limit of
jurisdiction over the marine resources by adjacent coastal States is
implemented, either as a result of the Law of the Sea Conferences or
unilaterally by the United States, we can expect commercial fishing
in the eastern Bering Sea to be more tightly regulated. Such action
should result in a reduction in harvest of those fish species now in
a depleted condition, which, in turn, could influence the abundance
of marine birds. Now is an opportune time to implement the studies
required to increase our knowledge of the abundance, distribution, and
seasonal movements of marine birds and their relationship to commercial
fish resources of the eastern Bering Sea.
Conclusions
• The eastern Bering Sea is a region of high biological productivity;
it is one of the world's great producers of commercial fish and major
congregating areas for marine birds.
• The vulnerability of fish to predation by marine birds depends on
life history features, such as place of spawning, duration of larval
stages, growth rate, sea temperature, and adult size of fish, and on
the distribution, feeding behavior, and food habits of marine birds.
[Illustration: =Fig. 9.= Sea temperatures in Bristol Bay and
southeastern Bering Sea in mid-June and early July of 1967 and 1971
(from Straty 1974).]
• The most apparent predation by marine birds on fish is on fish large
or mature enough that some hard body parts persist and can be found in
the stomach samples of birds.
• Little is known of the extent of bird predation on the pelagic eggs
and larvae of demersal fish and shellfish in the Bering Sea because of
lack of investigation and the rapid digestion of eggs and larvae by
birds.
• Predation by marine birds on juvenile salmon is not well documented
because of the lack of investigation in areas where both birds and fish
are present.
• Marine birds and commercial fish eat similar zooplankton and fish in
the eastern Bering Sea. The food exploited by both generally reflects
the relative abundance of the types of food in the area, but food
preference is displayed by some species of fish and birds.
• More is known about the food habits of the commercial fish than of
the marine birds of the Bering Sea.
• Sea water temperature may be a major environmental factor in the
Bering Sea since it influences both the extent to which fish are
vulnerable to predation and the amount of competition with marine
birds. Sea temperatures may vary greatly from year to year in the
Bering Sea, and this may result in variations in the magnitude of
predation and competition between birds and fish.
• The distribution of marine birds and the various stages in the life
history of commercial fish are not well known for the eastern Bering
Sea. Where these have been studied, they are intimately related. Such
knowledge is required to gain some insight into even the potential
for predation and competition in the dynamics of the marine bird and
commercial fish populations of this region. In two instances, it is
known that the occurrence of marine birds and the early life history
stages of fish coincide so as to result in both potential predation on
the fish by the birds and competition for food between the fish and the
birds.
• The possibility exists that the commercial fish resources of the
eastern Bering Sea will eventually come under the jurisdiction of the
United States. This could mean reduced harvests of fish to restore
depleted stocks. Such action could result in changes in the abundance
of the marine birds of this region by creating an increased food supply
for some and decreased supply for others.
Acknowledgments
We thank J. C. Bartonek and H. R. Carlson, H. Jaenicke, H. Larkins, and
B. L. Wing for supplying various materials presented in this paper.
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FOOTNOTES:
[54] For crabs, this measurement is carapace width.
[55] Authors' data.
[56] For crabs, the measurements are total length for zoeal stages and
carapace length and width for postzoeal stages.
[57] The incubation period for an egg is temperature dependent. Embryo
development is faster at higher temperatures.
[58] Juvenile pollock have diurnal migrations.
[59] The peak period varies with latitude: to 55°N--June; to
55-60°N--July; to north of 60°N--August.
[60] H. R. Carlson and R. E. Haight (in preparation), Juvenile life
of Pacific ocean perch, _Sebastes alutus_, in coastal fiords of
southeastern Alaska: their environment, growth, food habits, and
schooling behavior.
[61] The genus _Sebastes_ is a live bearer.
[62] Rockfish larvae resemble each other quite closely, and complete
descriptions for the 10 species in the Bering Sea do not exist. The
following depth distribution for rockfish larvae may or may not include
_S. alutus_: 45-365 m (Taylor 1967) off British Columbia; 0-88 m
(Ahlstrom 1959, 1961) off California and Baja California.
[63] In crabs, the eggs are attached to the female.
[64] S. C. Jewett and R. E. Haight (in preparation), A description of
megalopa of the snow crab, _Chionoecetes bairdi_ Rathbun (Majidae,
subfamily Oregoniinae).
[65] Spawning occurs in May in the eastern Bering Sea, but the total
period is not known.
Interrelations Between Seabirds and Introduced Animals
by
Robert D. Jones, Jr.
U.S. Fish and Wildlife Service
1011 East Tudor Road
Anchorage, Alaska 99507
and
G. Vernon Byrd[66]
U.S. Fish and Wildlife Service
Aleutian Islands National Wildlife Refuge
Adak, Alaska
Abstract
Animals introduced to insular seabird habitats
are of both intentional and accidental origin.
The results of the introductions--particularly
of herbivores--cannot be predicted, but may
range from severely destructive to beneficial.
Herbivores are of both domestic and wild
stocks of ungulates, hares, and rabbits. Rats
are the most commonly introduced omnivore on
a worldwide basis. In Alaska the commonest
carnivore introduction has been the red fox
_(Vulpes fulva)_ and arctic fox _(Alopex
lagopus)_, and the first of these were made in
the early 19th century by the Russian-American
Company. These foxes nearly extirpated the
Aleutian Canada goose _(Branta canadensis
leucopareia)_ from its nesting grounds. Black
flies (Simuliidae), which are vectors of avian
blood parasites, have been introduced to three
of the Aleutian Islands.
The purpose of this paper is to discuss some influences of introduced
animals, primarily mammals, on seabirds and their nesting habitat, with
emphasis on the coasts of Washington, British Columbia, and Alaska.
Our discussion focuses on island introductions partly because a large
proportion of seabirds choose island nesting sites, and because islands
present ecosystems vulnerable to such introductions.
Flightless animals have no means of immigration, hence little
probability of colonizing islands. In these circumstances marine birds
evolve populations in relatively simple ecosystems (Carlquist 1965;
MacArthur and Wilson 1967), though the degree of simplicity depends
on several variables, including the island's size and its distance
from a source of immigrants. These systems have achieved ecological
homeostasis through reciprocal adaptation over an extended period.
Experience has shown that introductions to such systems result in
severe perturbations (Odum 1971:221).
The introductions can be categorized as being either intentional or
accidental events. Effects of such introductions have varied widely,
depending on the type of animal introduced, the types of birds present
and the habitat they occupy, the size and shape of the island, the type
of nesting area used by the birds, and the status of their populations
before the introduction. An example drawn from our Aleutian experience
with gallinaceous birds illustrates the interaction of these variables.
The dark phase of the arctic fox _(Alopex lagopus)_ was introduced to
Adak and Amchitka islands, both of which had native populations of the
rock ptarmigan, _Lagopus mutus_ (Gabrielson and Lincoln 1959). Foxes
were released on Adak in 1924, and on Amchitka in 1921. Adak has an
area of 751 km² and Amchitka 350 km². Adak is irregular in shape with
extensive precipitous shorelines, relatively few beaches, and a large,
central mountainous hinterland which foxes rarely penetrated. Amchitka,
on the other hand, presents a zone of marine planation on its eastern
two thirds, low mountains on the rest, shelving beaches around most
of the island, and a long, linear, narrow shape that foxes explored
completely. By 1949 ptarmigan were difficult to find on Amchitka, and
then only in the highest, steepest section of the mountains. They were
extirpated from the low, eastern two thirds of the island. The foxes
flourished on Amchitka, but did much less well on Adak, where the
ptarmigan population fluctuated in a normal cyclic manner, apparently
uninfluenced by the foxes. Then the foxes were eradicated on Amchitka
in the 1950's, and by 1962 the ptarmigan had spread over the whole of
the island and become one of the most conspicuous avian features of the
landscape.
Animal Introductions
_Non-predatory Animals_
Man has taken ungulates with him to many islands. Although numerous
records of livestock introductions are available, few provide
information relating to the effects of these animals on the habitat and
their fauna unless the impact has been severe.
A most noteworthy example of destruction by ungulates occurred on
Guadalupe Island off the coast of Baja California. Domestic goats
_(Capra hircus)_ were introduced in the unrecorded past with the
result that little of the once abundant vegetation remains. In its
place introduced species capable of withstanding heavy grazing are
abundant over most of the island. Several endemic avian species are now
considered extinct, including the Guadalupe storm-petrel, _Oceanodroma
macrodactyla_ (Howell and Cade 1954; Jehl 1972).
Sheep _(Ovis aries)_ have been introduced to seabird nesting islands
with varying results. In Bass Strait, Australia, Norman (1970) studied
the effects of introduced sheep on vegetation and birds. He cited
various papers attributing destruction of colonies of shearwaters
(_Puffinus_ sp.) to the activities of sheep, primarily their treading
on the burrows. He found, however, that on Big Green Island and Phillip
Island, sheep were not responsible for declines in shearwater breeding
success, nor did they prevent expansion of colonies.
Other authors have reported damage to seabird nesting areas by
sheep. One such example in the eastern North Pacific region concerns
Protection Island, Washington. According to Richardson (1961), 100 to
300 sheep grazed freely on the island since 1958. He reported damage
by grazing and frequent trampling of nesting areas of rhinoceros
auklets _(Cerorhinca monocerata)_. Landslides were initiated by these
activities, rendering the slopes unusable by auklets. Of the burrows
in his study area, 46% were buried by slides. He did not determine
mortality.
Other avian consequences may flow from sheep introductions. Husbandry
of these ungulates has been practiced with varying success for many
years in the Aleutian Islands, most notably on Umnak and Unalaska
islands, both of which have large native populations of bald eagles,
_Haliaeetus leucocephalus_ (Gabrielson and Lincoln 1959). Before the
introduction of sheep, these raptors were oriented to the sea, hunting
fish and seabirds. Sheep presented a new resource and presently the
industry found itself confronted by a formidable predator, and demanded
that eagles be destroyed (letter to William Egan, Governor of Alaska,
from James S. Bynum, Secretary-treasurer, Umnak Company, Inc.).
Other ungulates introduced on Alaska islands include cattle _(Bos
taurus)_ on Chernofski and Chernabura islands; caribou _(Rangifer
tarandus)_ on Adak; reindeer on St. Matthew, Nunivak, Atka, Umnak, St.
Paul, St. Lawrence, Hagemeister, and Kodiak as well as many interior
locations; deer _(Odocoileus hemionus)_ on Kodiak and Afognak; elk
_(Cervus canadensis)_ on Afognak; and musk oxen _(Ovibos moschatus)_
on Nunivak. All these animals have maintained populations on islands
for a time, and some appear likely to do so into the distant future.
Specific effects on seabirds is generally not known, but trampling of
grassy slopes such as that reported for sheep develops in some cases.
Bailey et al. (1933) speculated that nests of the snow goose _(Anser
caerulescens)_ were destroyed by reindeer or their herdsmen in the
Point Barrow area.
The destruction of vegetation by introduced rabbits and hares has been
documented for many areas in the world. This destruction has often
extended to seabirds. Perhaps the most dramatic example occurred on
Laysan Island in the Hawaiian archipelago, where rabbits of unknown
species were introduced in 1903. According to Warner (1963) it took
less than 20 years for the rabbits to remove every green plant but
three patches of _Sesuvium portulacastrum_. The Laysan duck _(Anas
laysanensis)_ was brought perilously close to extinction. The rabbits
were eliminated in the 1920's, and the population of ducks increased to
over 600 by 1963, a figure thought to approximate the pre-disturbance
population.
European hares _(Lepus europaeus)_ were introduced on Smith, San Juan,
and Long islands, in Washington. On Smith Island, these burrowing
animals apparently grazed nearly all the succulent vegetation close to
the ground. By 1924, their burrows riddled the bluffs, causing them
to cave into the ocean (Couch 1929). Couch found no seabirds nesting
on the island, but found numerous tufted puffins _(Lunda cirrhata)_
present on the bluffs, but not nesting. A removal campaign was directed
against the hares in 1924 and in a few years they were gone. Smith
Island now supports nesting pelagic birds (D. Manuwal, personal
communication).
Accounts of hare and rabbit introductions to islands are legion, but
not all such introductions have drastically affected seabirds. Manana
Island, Hawaii, is such a case. Tomich et al. (1968) believed that
introduced rabbits _(Oryctolagus cuniculas)_ were not even indirectly
detrimental to the nesting noddies _(Anous tolidus)_ and sooty terns
_(Sterna fuscata)_. In some situations, introduced lagomorphs have
been credited with benefiting seabirds. Lockley (1942) suggested that
rabbits helped to open new breeding colonies of manx shearwaters
_(Puffinus puffinus)_ at Skomer and in west Wales in general. In Alaska
rabbits were introduced to Middleton Island in 1952 (Rausch 1958) and
to Ananiuliak Island at an earlier unrecorded date. Both have developed
sustaining populations in the presence of large seabird populations
without measurable effect on the birds. On Ananiuliak glaucous-winged
gulls _(Larus glaucescens)_ have been observed feeding on rabbits (W.
S. Laughlin, personal communication).
Invertebrates have been introduced on three islands in the Aleutians.
The black fly (_Simulium_ sp.) reached Adak by 1958, Shemya by 1964,
and Amchitka in connection with activities of the Atomic Energy
Commission in 1968. Apparently the insects were transported on jet
aircraft. The pest appears well established on Adak, but its status
on the other two islands is uncertain. Like the mosquito, the female
black fly sucks blood from warm-blooded animals, and in the process
becomes the vector of a _Leucocytozoan_ blood parasite of birds. In
years of black fly abundance at Seney (Michigan) National Wildlife
Refuge the blood parasite has been responsible for reproductive failure
in Canada geese (_Branta canadensis_; Sherwood 1968). If black fly
problems reach such a scale in the Aleutians, the parasites might prove
limiting to pelagic birds as well as to waterfowl. Winds, for which the
Aleutian region is famous, constitute a limiting factor for obligate
blood-feeding Simuliids and may control the severity of this problem.
_Predatory Animals_
The list of introduced animals that prey on seabirds is extensive.
Often several animals have been introduced to the same island. For
example, in 1951 Amchitka Island in the Aleutians supported populations
of feral dogs _(Canis familiaris)_ and cats _(Felis catus)_, rats
_(Rattus norvegicus)_, and arctic fox. Their presence resulted
from three of the usual sources of predator introductions: escape
of pets, escape from visiting ships (and aircraft), and commercial
introductions. Add introductions to control pests, such as that of
the mongoose _(Herpestes auropunctatus)_ to the Hawaiian Islands, and
only one source remains--the desire of man to improve on nature. In
the Aleutians this impulse has taken the more innocuous form of fish
and plant introductions, such as rainbow trout _(Salmo gairdneri)_ on
Adak and Shemya, and trees (mostly Sitka spruce, _Picea sitkensis_) on
every military base in the "Chain."
Rats appear to be the most commonly introduced predators on a worldwide
scale. Ships furnish the traditional source of their introduction,
but one of us (R.D.J.) has observed them disembarking from a military
aircraft at Cold Bay on the Alaska Peninsula. These animals probably
entered the plane at Adak, which received rats from military ships
early in World War II.
Rats may be able to exploit a larger percentage of the seabird species
on a given island than other introduced predators because they can
enter crevices and burrows in search of the birds and their eggs and
young. They also destroy ground-nesters, and cliff-nesters may not be
altogether safe from them. Clayton M. White (personal communication)
found that _Rattus norvegicus_ had ravaged every one of 16 eyries of
the peregrine falcon _(Falco peregrinus)_ that he checked in 1971 at
Amchitka Island, Alaska. Only one egg had tooth marks, however. Kenyon
(1961) ascribed the disappearance of the song sparrow _(Melospiza
melodia maxima)_ and the winter wren _(Troglodytes troglodytes
kiskensis)_ from Amchitka to predation by rats.
Many authors have mentioned potential rat damage, but few have
quantitatively documented it. Imber (1974), however, provided
data concerning the magnitude of rat predation on diving petrels
and storm-petrels on some New Zealand islands. He found that rats
were taking between 10 and 35% of the chicks of gray-faced petrels
_(Pterodroma macroptera gouldi)_ on Whale Island in the parts of the
colonies where burrows were dense. On those parts of the island with a
very low density of petrel burrows, rats were believed to have killed
virtually every chick. Imber revealed that where Polynesian rats
_(Rattus exulans)_ occur, diving petrels and storm-petrels are rare
or absent, though they are widespread on neighboring islands. Imber
concluded from his studies of the ecology of petrels and Polynesian and
Norway rats that a petrel colony is endangered if invaded by a species
of rat whose maximum weight approaches or exceeds the mean adult weight
of the petrel. Harris (1970), who worked with dark-rumped petrels
_(Pterodroma phacopygia)_ on Santa Cruz in the Galapagos Islands,
indicated that black rats _(Rattus rattus)_ were responsible for the
extremely low nesting success of the petrels there.
In British Columbia, Campbell (1968) recorded predation by the
Alexandrian rat _(R. rattus)_ on ancient murrelets _(Synthliboramphus
antiquus)_ at Langara Island. The extent of damage to the murrelet
population is not known.
The animals most widely introduced in Alaska seabird habitat are the
red fox _(Vulpes fulva)_ and the arctic fox. The red fox is native
to the Alaska Peninsula and to the easternmost group of islands in
the Aleutians, known as the Lissii or Fox Islands (Berkh 1823; Murie
1959). At the other end of the archipelago, in the group known as the
Near Islands, Attu Island has a native population of the arctic fox
(Tikhmenev 1861; Bancroft 1886). Between Umnak Island, the westernmost
island of the Fox group, and Attu there are no native terrestrial
mammals, and substantial avian populations evolved an ecology in the
absence of mammalian predation (Murie 1959).
At the time of Russian contact with the Aleutians, both fox species
were dominantly dark phase, and the early introductions (about 1836)
by the Russian-American Company were of both species (Tikhmenev
1861). Initially both species were successful in developing insular
populations, but in the long run the arctic fox proved the more
successful. At Great Sitkin, Adak, and Kanaga, introduced red foxes
maintained populations that were eliminated in the 1920's to be
replaced by arctic foxes (unpublished records of the Aleutian Islands
National Wildlife Refuge). Differential harvest of the preferred dark
phase had in the meantime altered the genetic makeup of the population,
and the light phase had become dominant. In the arctic fox populations,
the dark phase remained generally dominant at about 95%, but in some
small islands with limited genetic stock (e.g., the Semichis) the
proportion approached one to one (unpublished records of the Aleutian
Islands National Wildlife Refuge).
By 1936, the Aleutian archipelago constituted a large-scale fox farm,
which in its 23 years of existence as a refuge had produced 25,641 fox
pelts with a value of $1,162,826. During the same period, and perhaps
earlier, arctic foxes were introduced on almost every island from
the Aleutians to Prince William Sound, and on some of the islands in
southeastern Alaska. The Aleutian Islands National Wildlife Refuge
maintained records from which the above figures are quoted, but though
records of other islands' use for fur farms exist in the archives of
the Alaska Game Commission, no record of the fur values was kept.
Murie (1959) assessed the influence of the foxes by examining 2,501 fox
droppings collected in 1936 and 1937 from 22 of the Aleutian Islands.
He reported 57.8% of the food items in these droppings was avian--48.9%
seabirds. The result of his investigations was the adoption of new
policies governing issuance of permits for fox farming in the Refuge.
The essential feature of these policies was the revocation of certain
existing permits, with a view to reserving the islands concerned for
wildlife use. The decision proved academic, for fur prices declined
until no market for Aleutian arctic fox pelts could be found. But the
foxes remained.
The most obvious damage has been the nearly complete extermination
of the Aleutian Canada goose _(Branta canadensis leucopareia)_. It
has vanished from its former nesting range in the Aleutian and Kuril
Islands, except for Buldir Island in the western Aleutians (Jones
1963). Clark (1910) described this goose as extremely abundant on
Agattu Island in 1909; however, foxes from Attu were introduced there
in 1923, 1925, and 1929. Murie (1959) found "probably less than six
pairs" in 4 days of traveling over the island in 1937.
In our main area of interest, cats appear to have been widely
introduced, but we found no record of extensive predation on marine
birds. Jehl (1972) attributed the extinction of the Guadalupe petrel to
predation by cats, in combination with the destruction of vegetation
by goats. Imber (1974) reported that "serious predation by cats upon a
colony of gray-faced petrels on Little Barrier Island, New Zealand was
observed in 1950. Since that time, the colony has become extinct."
Though feral dogs are reported present on islands in our area of
interest, they do not appear to have significant influence on seabirds.
On Attu Island, the pet dogs of personnel of the Coast Guard LORAN
station are reported to take common eiders _(Somateria mollissima)_.
Conclusions
Ecological consequences of animal introductions to islands are rarely
well documented. Usually no thought is devoted to such consequences
until redress becomes difficult or quite impossible. Many of the
introductions stem from a period before ecological understanding, and
the introduced animal has acquired the status of a native. The arctic
fox in the Aleutians fits all of these conditions. Until we conducted
a thorough search of the literature, some of it difficult to secure
and written in several languages, the original status of this animal
was not known. Its elimination, now under way on selected islands,
is difficult and expensive. Rapid recovery of some avian species,
including certain passerines, has been observed. However, ecological
homeostasis is the product of evolution, and restoration in the
Aleutians must follow that course. It is not likely to proceed rapidly
to a point thought desirable by man. The accidental introductions
of animals such as rats and black flies in the Aleutians constitute
particularly irksome events because they cannot be reversed. The new
ecology of Amchitka, from which the foxes have been removed, must
evolve in the presence of these species. Its face will look very
different than if they were not there. We would like to suggest a means
by which such introductions may be prevented, but it seems likely that
more, not less, can be expected.
Preventing the introduction of ungulates seems more likely to be
successful, especially if the islands lie within a National Wildlife
Refuge. Even this, however, becomes less certain with an expanding
human population and, with it, demands for more land on which to
produce food.
Legal restrictions have been suggested as a means to control or prevent
introductions, but in the northern islands, little enforcement is
likely. There is a phrase bearing on this, said to have governed human
behavior in the early years of Caucasoid occupation of the Aleutian
Islands, "Heaven is too high and the Czar too far away."
References
Bailey, A. M., C. D. Brower, and L. B. Bishop. 1933. Birds of the
region of Point Barrow, Alaska. Prog. Act. Chic. Acad. Sci.
4(2):14-40.
Bancroft, H. H. 1886. History of Alaska, 1730-1885. San Francisco.
Berkh, V. 1823. The chronological history of the discovery of the
Aleutian Islands or the exploits of the Russian merchants. N.
Grech., St. Petersburg.
Campbell, R. W. 1968. Alexandrian rat predation on ancient murrelet
eggs. Murrelet 49:38.
Carlquist, S. 1965. Island life: a natural history of the islands
of the world. Natural History Press, New York.
Clark, A. H. 1910. The birds collected and observed during the
cruises of the United States Fisheries Steamer "Albatross" in
the North Pacific Ocean and in the Bering, Okhotsk, Japan, and
Eastern seas from April to December 1906. Proc. U.S. Natl. Mus.
38:25-74.
Couch, L. K. 1929. Introduced European rabbits in the San Juan
Islands, Washington. J. Mammal. 10:334-336.
Gabrielson, I. N., and F. C. Lincoln. 1959. The birds of Alaska.
Stackpole Co. and Wildlife Management Institute, Washington, D.C.
Harris, M. P. 1970. The biology of an endangered species, the
dark-rumped petrel (_Pterodroma phacopygia)_ in the Galapagos
Islands. Condor 72:76-84.
Howell, T. R., and T. J. Cade. 1954. The birds of Guadalupe Island
in 1953. Condor 56:283-291.
Imber, M. J. 1974. The rare and endangered species of the New
Zealand region and the policies that exist for their management:
petrels and predators. Paper presented to the International
Council for Bird Preservation (XVI World Conference), Canberra.
Jehl, J. R. 1972. On the cold trail of an extinct petrel. Pac.
Discovery 25:24-28.
Jones, R. D. 1963. Buldir Island, site of a remnant breeding
population of Aleutian Canada geese. Wildfowl Trust Annu. Rep.
14:80-84.
Kenyon, K. W. 1961. Birds of Amchitka Island, Alaska. Auk
78(3):305-326.
Lockley, R. M. 1942. Shearwaters. Devin-Adair, New York.
MacArthur, R. H., and E. O. Wilson. 1967. The theory of island
biogeography. Princeton Univ. Press, Princeton, N.J.
Murie, O. J. 1959. Fauna of the Aleutian Islands and Alaska
Peninsula. U.S. Fish Wildl. Serv., N. Am. Fauna 61:1-364.
Norman, F. I. 1970. The effects of sheep on the breeding
success and habitat of the short-tailed shearwater _(Puffinus
tenuirostris)_ (Temminch). Aust. J. Zool. 18:215-242.
Odum, E. P. 1971. Fundamentals of ecology. W. B. Saunders Co.,
Philadelphia, Pa. 574 pp.
Rausch, R. 1958. The occurrence and distribution of birds on
Middleton Island, Alaska. Condor 60(4):227-242.
Richardson, F. 1961. Breeding biology of the rhinoceros auklet on
Protection Island. Condor 63(6):456-473.
Sherwood, G. A. 1968. Factors limiting production and expansion
of local populations of Canada geese. Pages 73-85 _in_ R. L.
Hine and C. Schoenfeld, eds. Canada goose management. Dembar
Educational Research Service, Madison, Wis.
Tikhmenev, P. 1861. Historical review of the origin of the
Russian-American Co. and its activity up to and the present time.
Edward Weimar, St. Petersburg.
Tomich, P. Q., N. Wilson, and C. H. Lamoureux. 1968. Ecological
factors on Manana Island, Hawaii. Pac. Sci. 12:352-368.
Warner, R. E. 1963. Recent history and ecology of the Laysan duck.
Condor 65(1):2-23.
FOOTNOTES:
[66] Present address: Hawaiian Islands National Wildlife Refuge,
Kilauea, Hawaii.
Oil Vulnerability Index for Marine Oriented Birds
by
James G. King
U.S. Fish and Wildlife Service
P. O. Box 1287
Juneau, Alaska 99802
and
Gerald A. Sanger
U.S. Fish and Wildlife Service
Anchorage, Alaska
Abstract
The 176 species of birds using marine habitats
of the Northeast Pacific are graded on the
basis of 20 factors that affect their survival.
A score of 0, 1, 3, or 5, respectively,
representing no, low, medium, or high
significance is assigned for each factor. The
total score is the Oil Vulnerability Index
(OVI). The OVI's range from 1 to 100, an index
of 100 indicating the greatest vulnerability.
Using this system, one can rank the avifauna
of different areas according to their
vulnerability to environmental hazards as an
aid in making management decisions.
Today's decision makers require an ever-increasing array of information
and planning documents. The Federal Government's requirement for
environmental impact statements under the National Environmental
Protection Act of 1969 is but one example of this trend. These
documents generally consider the effects of proposed actions on
waterfowl and a few other species of birds, but the bulk of the
avifauna is usually only listed, or sometimes ignored completely. A
simple system for evaluating and presenting avian data is badly needed
so that those interested in birds, whether technically trained or not,
can easily grasp the implications of proposed actions. It is incumbent
on biologists to devise new ways of presenting their knowledge so that
it can be easily and effectively used by decision makers, who are often
less informed. In short, biologists must do for the environmental
impact statement assessors what Roger Tory Peterson did for the bird
watchers by giving them a simple and comprehensible system.
The need for a system to evaluate relative vulnerabilities of bird
populations is particularly great for birds that are being increasingly
affected by marine oil pollution. The system needs to allow comparisons
of potential impacts to birds resulting from various oil development
projects in different locations and served by various modes of
transport. The Oil Vulnerability Index (OVI) is our attempt to fulfill
this informational need on the avifauna of the Northeast Pacific.
Insofar as we know, this approach to assessing a wildlife management
problem has been attempted only for ranking endangered species in a
numeric ranking system that identified where restoration efforts could
best be directed (Sparrowe and Wight 1975).
We are indebted to Gene Ruhr and Keith Schreiner for ideas generated in
their work with endangered species. Frank Pitelka, James Bartonek, Kent
Wohl, and Mary Lou King reviewed portions of the manuscript and offered
helpful suggestions. Jack Hodges helped prepare the OVI tables.
Methods
A list of 176 species of birds using marine habitats in or near the
States of Washington and Alaska and the Province of British Columbia
(Table 1, left column) was compiled from checklists by the American
Ornithologists' Union (AOU 1957) and Gibson (1970). Nomenclature is
from AOU (1957). The scientific names of three species of shorebirds
recently identified in the Aleutian Islands that were not listed by the
AOU (1957) came from Peterson et al. (1967).
Each bird was scored on 20 factors that affect its survival (Table
1). Point scores for most birds were either 0, 1, 3, or 5, indicating
no, low, medium, or high importance, respectively, in their biology
or habits as related to Northeast Pacific oil development. Rare or
accidental species were given only one point for occurrence, and
endangered species 99 points for population size plus 1 point for
occurrence. Thus the potential range of the OVI's is from 1 to 100.
The factors in Table are largely self-explanatory. The items under
"range" apply to the entire world population of the species.
"Productivity" is derived from a combination of clutch size and age
at first nesting. Specialization is used in the biological sense to
compare a versatile species like mallards (_Anas platyrhynchos)_ with a
less versatile species such as the trumpeter swan _(Olor buccinator)_.
Mortality under "history of oiling" is based on our knowledge that
some species (e.g., alcids) have been more involved than others such
as gulls. Exposure relates to the level of exposure within the Pacific
area in any season.
Information on many of the factors for many species is scanty at best,
and subjective appraisals were made by us when information was lacking.
Opinions as to appropriate scores will vary among experts. References
used, in part, in preparing Table 1 were: AOU 1957; Fay and Cade 1959;
Gabrielson and Lincoln 1959; Isleib and Kessel 1973; Kortright 1942;
Murie 1959; Palmer 1962; Robbins et al. 1966; Sanger 1972; and Stout et
al. 1967.
Results
The OVI for each of 176 bird species is listed in Table 1. The average
OVI for 22 avian families comprising 128 species that are neither rare
stragglers nor endangered ranged from 19 to 88, with a mean of 51
(Table 3).
Tables 4 and 5 show a possible use for the OVI by comparing impacts
in two large, widely separated areas. A species list from Southeast
Alaska (U.S. Forest Service and Alaska Department of Fish and Game
1970) is compared with a list from the Aleutian Islands (U.S. Fish
and Wildlife Service 1974). Only commonly occurring species are
included. These tables graphically display rather strong differences
in the vulnerability of the avifauna of each area. A person explaining
comparative impacts of projects might use the tables in the following
way:
• Column 1, with scores from 1 to 20 points, indicates birds with a low
level of project involvement, where damage or future costs would not be
expected. As this will normally be the longest list, as in Tables 4 and
5, one would expect an immediate rise of interest on the part of the
planning agency, which is probably eager to learn where problems will
be fewest.
• Column 2 (21 to 40 points) indicates birds for which there is a low
level of concern. Perhaps all that is needed is a review to determine
if special characteristics of the project might be detrimental to these
species.
• Column 3 (41 to 60 points) might be called "trial and error" species.
If some birds are adversely affected, it will not be catastrophic. As
the project develops it will be merely necessary to monitor these to
make sure their status is not adversely affected. If it is, there will
be time to develop conservation measures.
• Columns 4 and 5 (61 to 80 points and 81 to 100 points, respectively)
include the species where concern is high. It is for these species
that research money will be needed, where project modifications may be
required, where a contingency plan in case of disaster is needed, where
a conservation technology will be needed, and where periodic project
shutdown could be called for.
Table 1. _Oil Vulnerability Index (OVI) for waterbirds in the
Northeast Pacific Region._
Range
|Breeding range size
| |Migration length
| | |Winter range size
| | | |Marine orientation
| | | |
| | | | Population
| | | | |Population size
| | | | | |Productivity
| | | | | |
| | | | | | Habits
| | | | | | |Roosting
| | | | | | | |Foraging
| | | | | | | | |Escape
| | | | | | | | | |Flocking on water
| | | | | | | | | | |Nesting density
| | | | | | | | | | | |Specialization
| | | | | | | | | | | |
| | | | | | | | | | | | Mortality
| | | | | | | | | | | | |Hunted by man
| | | | | | | | | | | | | |Animal depredations
| | | | | | | | | | | | | | |Non-oil pollution
| | | | | | | | | | | | | | | |History of
| | | | | | | | | | | | | | | | oiling
| | | | | | | | | | | | | | | | |Annual
| | | | | | | | | | | | | | | | | exposure
| | | | | | | | | | | | | | | | |Spring
| | | | | | | | | | | | | | | | | |Summer
| | | | | | | | | | | | | | | | | | |Fall
| | | | | | | | | | | | | | | | | | | |Winter
| | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | | |OVI
Family, common (AOU) name and | | | | | | | | | | | | | | | | | | | | |Total
scientific name | | | | | | | | | | | | | | | | | | | | |Points
-------------------------------------------------------------------------------
Gaviidae
Common loon _(Gavia immer)_ 1 3 3 3 1 5 5 5 5 1 1 3 1 1 3 3 1 0 1 1 47
Yellow-billed loon
_(G. adamsii)_ 3 3 5 3 5 5 5 5 5 1 1 3 1 1 0 3 5 1 5 5 65
Arctic loon _(G. arctica)_ 3 3 3 3 3 5 5 5 5 1 1 3 1 1 3 3 3 1 3 3 58
Red-throated loon
_(G. stellata)_ 1 3 3 5 1 5 5 5 5 1 1 3 1 1 3 3 1 0 1 1 49
Podicipedidae
Red-necked grebe (_Podiceps_
_grisegena_) 1 3 3 3 1 3 5 5 5 1 1 3 0 1 3 3 1 0 1 1 44
Horned grebe _(P. auritus)_ 1 3 3 3 1 3 5 5 5 3 1 3 0 3 3 3 1 0 1 1 48
Western grebe (_Aechmophorus_
_occidentalis_) 3 3 3 5 1 3 5 5 5 5 1 3 0 1 3 5 1 0 1 3 56
Diomedeidae
Short-tailed albatross
_(Diomedea albatrus)_ 99 1 100
Black-footed albatross
_(D. nigripes)_ 5 1 1 5 3 5 5 3 3 1 5 5 0 0 1 3 1 1 1 1 50
Laysan albatross
_(D. immutabilis)_ 5 1 1 5 3 5 5 3 3 1 5 5 0 0 1 3 1 1 1 3 52
Procellaridae
Fulmar _(Fulmarus glacialis)_ 3 3 1 5 1 5 5 3 3 3 5 3 0 1 1 3 3 3 3 3 57
Pink-footed shearwater
_(Puffinus creatopus)_ 3 1 1 5 1 5 5 3 3 3 5 3 0 1 1 3 1 1 1 1 47
Pale-footed shearwater
_(P. carneipes)_ 1 1
New Zealand shearwater
_(P. bulleri)_ 1 1
Sooty shearwater
_(P. griseus)_ 1 1 1 5 1 5 5 3 3 5 5 3 1 1 1 3 1 5 1 0 51
Slender-billed shearwater
_(P. tenuirostris)_ 1 1 3 5 1 5 5 3 3 5 5 3 1 1 1 3 1 5 1 0 53
Scaled petrel (_Pterodroma_
_inexpectata_) 1 1
Cooks petrel _(P. cookii)_ 1 1
Hydrobatidae
Fork-tailed storm-petrel
_(Oceanodroma furcata)_ 3 3 3 5 1 5 5 3 3 3 5 3 0 1 1 3 5 5 5 5 67
Leach's storm-petrel
_(O. leucorhoa)_ 1 3 1 5 1 5 5 3 3 3 5 3 0 1 1 3 5 5 5 5 63
Pelecanidae
Brown pelican
_(Pelecanus occidentalis)_ 1 1
Phalacrocoracidae
Double-crested cormorant
_(Phalacrocorax auritus)_ 1 3 3 3 3 3 1 5 3 1 3 3 0 1 3 5 3 3 5 52
Brandt's cormorant
_(P. penicillatus)_ 3 3 3 5 3 3 1 5 3 1 3 3 0 1 3 5 3 3 3 3 57
Pelagic cormorant
_(P. pelagicus)_ 3 3 3 5 3 3 1 5 3 3 3 3 0 1 3 5 5 1 5 5 63
Red-faced cormorant
_(P. urile)_ 5 3 3 5 3 3 1 5 3 3 3 3 0 1 1 5 5 5 3 3 63
Ardeidae
Great blue heron
_(Ardea herodias)_ 1 3 1 1 3 3 1 1 1 1 3 3 0 1 1 1 1 1 1 1 29
Anatidae
Whooper swan _(Olor cygnus)_ 1 1
Whistling swan
_(O. columbianus)_ 3 3 3 3 3 3 5 3 1 5 1 3 3 1 3 1 3 0 3 0 50
Trumpeter swan
_(O. buccinator)_ 5 5 3 3 5 3 5 5 1 5 1 5 1 1 3 3 3 0 3 3 63
Canada goose
_(Branta canadensis)_ 1 3 1 1 5 3 1 1 1 3 1 1 5 1 1 1 1 1 1 1 34
Black Brant _(B. nigricans)_ 3 3 3 5 3 3 5 5 3 5 3 3 5 1 3 5 3 1 5 3 70
Emperor goose
_(Philacte canagica)_ 3 5 5 5 3 3 3 3 3 3 3 3 3 1 1 5 5 3 5 5 70
White-fronted goose
_(Anser albifrons)_ 3 3 3 1 3 3 1 1 1 1 1 1 5 1 3 1 1 1 1 1 36
Snow goose
_(Chen hyperborea)_ 1 3 1 1 3 3 1 1 1 1 1 1 5 1 3 1 1 1 1 1 32
Mallard
_(Anas platyrhynchos)_ 1 3 1 1 1 1 1 3 3 3 1 1 5 3 3 1 1 1 1 1 36
Gadwall _(A. strepera)_ 3 3 1 1 1 1 1 3 3 3 1 1 5 3 3 1 1 1 1 1 38
Pintail _(A. acuta)_ 1 3 1 1 1 1 1 3 3 3 1 1 5 3 3 1 1 1 1 1 36
Common teal _(A. crecca)_ 1 1
Green-winged teal
_(A. carolinensis)_ 1 3 1 1 1 1 1 3 3 1 1 1 5 3 3 1 1 1 1 1 34
Blue-winged teal
_(A. discors)_ 1 1
Cinnamon teal
_(A. cyanoptera)_ 1 1
European wigeon
_(Mareca penelope)_ 1 1
American wigeon
_(M. americana)_ 1 3 1 1 1 1 1 3 3 3 1 1 5 3 3 1 1 1 1 1 36
Shoveler
_(Spatula clypeata)_ 1 3 1 1 1 1 1 3 3 1 1 1 5 3 3 1 1 1 1 1 34
Redhead
_(Aythya americana)_ 1 3 1 1 5 3 5 5 5 3 1 3 5 1 3 3 1 1 1 1 52
Ring-necked duck
_(A. collaris)_ 1 1
Canvasback
_(A. valisineria)_ 1 3 1 1 5 3 5 5 5 3 1 3 5 1 3 3 1 1 1 1 52
Greater scaup
_(A. marila)_ 1 3 1 5 1 3 5 5 5 3 1 3 5 1 3 3 1 1 1 1 52
Lesser scaup
_(A. affinis)_ 1 3 1 3 1 3 5 5 5 3 1 3 5 1 3 3 1 1 1 1 50
Common goldeneye
_(Bucephala clangula)_ 1 3 1 3 1 3 5 5 5 3 1 3 3 1 3 3 1 1 1 1 48
Barrow's goldeneye
_(B. islandica)_ 3 3 1 3 1 3 5 5 5 3 1 3 3 1 3 3 3 1 3 3 56
Bufflehead
_(B. albeola)_ 1 3 1 3 1 3 5 5 5 3 1 3 1 1 3 3 3 1 3 3 52
Oldsquaw
_(Clangula hyemalis)_ 1 3 1 5 1 3 5 5 5 5 1 3 3 1 1 5 5 3 5 5 66
Harlequin duck
_(Histrionicus
histrionicus)_ 3 5 1 5 1 3 1 3 3 3 1 3 1 1 1 5 5 5 5 5 60
Steller's eider
_(Polysticta stelleri)_ 3 3 5 5 1 3 5 5 5 5 1 3 3 1 1 5 5 3 5 5 72
Common eider
_(Somateria mollissima)_ 3 5 3 5 1 3 5 5 5 3 1 3 1 1 1 5 5 3 5 5 68
King eider
_(S. spectabilis)_ 3 5 3 5 1 3 5 5 5 5 1 3 1 1 1 5 5 3 5 5 70
Spectacled eider
_(Lampronetta fisheri)_ 5 5 5 5 3 3 5 5 5 5 3 3 1 1 1 5 5 3 5 5 78
White-winged scoter
_(Melanitta deglandi)_ 3 3 3 3 1 3 5 5 5 5 1 3 3 1 3 5 5 5 5 5 72
Surf scoter
_(M. perspicillata)_ 3 3 3 3 1 3 5 5 5 5 1 3 3 1 3 5 5 5 5 5 72
Common scoter
_(Oidemia nigra)_ 3 3 3 3 1 3 5 5 5 5 1 3 3 1 3 5 5 5 5 5 72
Ruddy duck
_(Oxyura jamaicensis)_ 1 3 1 3 1 1 5 5 5 5 1 5 5 3 3 3 1 0 1 3 55
Hooded merganser
_(Laphodytes cucullatus)_ 1 3 1 1 3 3 3 5 3 1 1 3 1 1 3 1 1 0 1 1 37
Common merganser
_(Mergus merganser)_ 1 3 3 3 1 3 3 5 5 3 1 3 3 1 3 3 3 3 3 3 56
Red-breasted merganser
_(M. serrator)_ 1 3 3 3 1 3 3 5 5 3 1 3 3 1 3 3 3 3 3 3 56
Accipitridae
Bald eagle
_(Haliaeetus leucocephalus)_ 1 5 3 3 5 5 0 1 1 0 1 5 0 0 5 3 5 5 5 5 58
Steller's sea eagle
_(H. pelagicus)_ 1 1
Marsh hawk _(Circus cyaneus)_ 1 3 1 1 1 3 1 1 1 0 1 1 0 0 1 1 1 0 1 0 19
Pandionidae
Osprey _(Pandion haliaetus)_ 1 3 1 1 5 5 0 1 1 0 1 5 3 1 5 1 1 1 1 0 37
Falconidae
Peregrine falcon
_(Falco peregrinus)_ 1 3 1 1 5 5 0 1 1 0 1 3 3 0 5 1 3 3 3 1 41
Gruidae
Sandhill crane
_(Grus canadensis)_ 1 3 1 1 1 3 1 1 1 0 1 1 3 1 1 1 1 1 1 0 24
Rallidae
American coot
_(Fulica americana)_ 1 3 1 1 1 1 3 3 1 3 1 1 3 3 3 1 1 0 1 1 33
Haematopodidae
Black oystercatcher
_(Haematopus bachmani)_ 5 5 5 5 3 5 1 1 1 1 1 5 0 1 3 3 5 5 5 5 65
Charadriidae
Ringed plover
_(Charadrius hiaticula)_ 1 1
Semipalmated plover
_(C. semipalmatus)_ 1 1 1 1 1 3 1 1 1 1 1 1 0 5 1 1 3 1 3 0 28
Mongolian plover
_(C. mongolus)_ 1 1
Killdeer _(C. vociferus)_ 1 3 1 1 1 3 1 1 1 1 1 1 0 5 1 1 1 1 1 0 26
Dotterel
_(Eudromias morinellus)_ 1 1
American golden plover
_(Pluvialis dominica)_ 1 1 1 3 3 3 3 1 1 3 1 3 3 5 0 1 1 0 1 0 35
Black-bellied plover
_(Squatarola squatarola)_ 1 1 1 5 3 3 1 1 1 3 1 3 3 5 1 3 3 1 3 0 43
Surfbird _(Aphriza virgata)_ 5 1 5 5 3 3 1 1 1 3 1 3 0 5 1 3 5 0 5 3 54
Ruddy turnstone
_(Arenaria interpres)_ 1 1 3 5 3 3 1 1 1 3 1 3 0 5 1 3 3 3 3 0 44
Black turnstone
_(A. melanocephala)_ 5 3 3 5 3 3 1 1 1 3 1 3 0 5 1 3 5 3 5 3 57
Scolopacidae
Common snipe
_(Capella gallinago)_ 1 1 1 1 1 3 1 1 1 1 1 1 5 5 1 1 1 1 1 0 29
Eurasian curlew
_(Numenius arquata)_ 1 1
Whimbrel _(N. phaeopus)_ 1 1 1 3 3 3 1 1 1 3 1 3 1 3 1 3 3 1 3 0 37
Bristle-thighed curlew
_(N. tahitiensis)_ 5 1 1 5 5 3 3 1 1 3 1 1 1 3 1 3 3 1 3 0 45
Eskimo curlew _(N. borealis)_ 99 1 100
Upland plover
_(Bartramia longicauda)_ 1 1 1 0 5 3 1 1 1 0 1 1 3 3 1 0 1 1 1 0 26
Spotted sandpiper
_(Actitis macularia)_ 1 3 1 1 1 3 1 1 1 1 1 1 0 3 1 1 1 1 1 0 24
Common sandpiper
_(Tringa hypoleucos)_ 1 1
Solitary sandpiper
_(T. solitaria)_ 1 1
Wood sandpiper
_(T. glareola)_ 1 1
Wandering tattler
_(Heteroscelus incanum)_ 5 1 1 5 5 3 1 1 1 3 1 3 1 3 1 3 5 0 5 0 48
Polynesian tattler
_(H. brevipes)_ 1 1
Willet
_(Catoptrophorus
semipalmatus)_ 1 1
Greater yellowlegs
_(Totanus melanoleucus)_ 1 5 1 1 3 3 1 1 1 1 1 1 3 3 1 1 1 0 1 0 30
Lesser yellowlegs
_(T. flavipes)_ 1 5 1 1 3 3 1 1 1 1 1 1 3 3 1 1 1 0 1 0 30
Spotted redshank
_(T. totanus)_ 1 1
Greenshank
_(Tringa nebularia)_ 1 1
Knot _(Calidris canutus)_ 1 1 1 5 5 3 1 1 1 3 1 1 1 3 1 3 3 3 1 0 39
Great knot
_(C. tenuirostris)_ 1 1
Rock sandpiper
_(Erolia ptilocnemis)_ 5 3 3 5 3 3 1 1 1 3 1 3 0 3 1 3 5 5 5 5 59
Sharp-tailed sandpiper
_(E. acuminata)_ 3 1 3 5 3 3 1 1 1 3 1 3 0 3 3 3 3 0 3 3 46
Pectoral sandpiper
_(E. melanotos)_ 1 1 3 1 3 3 1 1 1 1 1 1 0 3 1 1 3 3 3 0 32
White-rumped sandpiper
_(E. fuscicollis)_ 1 1
Baird sandpiper
_(E. bairdii)_ 1 3 3 1 3 3 1 1 1 1 1 1 0 3 1 1 3 3 3 0 34
Least sandpiper
_(E. minutilla)_ 1 3 3 3 1 3 1 1 1 1 1 1 0 3 1 1 3 3 3 0 34
Long-toed stint
_(E. subminuta)_ 1 1
Temminck's stint
_(Calidrus temminckii)_ 1 1
Rufous-necked sandpiper
_(E. ruficollis)_ 3 1 3 5 3 3 1 1 1 3 1 1 0 3 1 3 1 1 1 0 36
Curlew sandpiper
_(E. ferruginea)_ 1 1
Dunlin _(E. alpina)_ 1 3 1 5 1 3 1 1 1 1 1 1 0 3 3 3 3 3 3 3 41
Short-billed dowitcher
_(Limnodromus griseus)_ 3 3 3 3 3 3 1 1 1 1 1 3 3 3 1 3 3 3 3 0 45
Long-billed dowitcher
_(L. scolopaceus)_ 5 3 3 3 3 3 1 1 1 1 1 3 3 3 1 3 3 3 3 0 47
Stilt sandpiper
_(Micropalama himantopus)_ 1 1
Semipalmated sandpiper
_(Ereunetes pusillus)_ 1 3 1 3 1 3 1 1 1 1 1 1 0 3 1 1 3 5 3 0 34
Western sandpiper
_(E. mauri)_ 5 3 3 5 1 3 1 1 1 1 1 1 0 3 3 3 3 5 3 1 47
Buff-breasted sandpiper
_(Tryngites subruficollis)_ 1 1
Marbled godwit
_(Limosa fedoa)_ 1 1
Bar-tailed godwit
_(L. lapponica)_ 3 1 1 5 3 3 1 1 1 3 1 3 3 3 1 3 5 5 3 0 49
Hudsonian godwit
_(L. haemastica)_ 1 1
Black-tailed godwit
_(L. limosa)_ 1 1
Ruff _(Philomachus pugnax)_ 1 1
Sanderling _(Crocethia alba)_ 3 1 1 5 3 3 1 1 1 3 1 3 0 3 1 3 3 3 3 3 45
Spoon-billed sandpiper
_(Eurynorhynchus pygmeum)_ 1 1
Phalaropodidae
Red phalarope
_(Phalaropus fulicarius)_ 3 1 1 5 1 3 5 5 1 5 1 5 0 3 1 5 5 3 5 0 58
Wilson's phalarope
_(Steganopus tricolor)_ 1 1
Northern phalarope
_(Lobipes lobatus)_ 3 1 3 5 1 3 5 5 1 5 1 5 0 3 3 5 5 3 5 0 62
Stercorariidae
Pomarine jaeger
_(Stercorarius pomarinus)_ 1 1 1 5 1 3 3 3 1 3 1 3 1 1 1 3 3 3 3 0 41
Parasitic jaeger
_(S. parasiticus)_ 1 1 1 5 1 3 3 3 1 3 1 3 1 1 3 3 3 3 3 0 43
Long-tailed jaeger
_(S. longicaudus)_ 1 1 1 3 1 3 3 3 1 3 1 3 1 1 1 3 3 3 3 0 39
Skua _(Catharacta skua)_ 1 1
Laridae
Glaucous gull
_(Larus hyperboreus)_ 1 5 3 3 1 3 3 3 1 3 3 1 0 1 1 1 3 3 3 3 45
Glaucous-winged gull
_(L. glaucescens)_ 5 1 3 5 1 3 3 3 1 3 5 1 1 1 1 1 5 5 5 3 56
Slaty-backed gull
_(L. schistisagus)_ 1 1
Western gull
_(L. occidentalis)_ 3 1 3 5 1 3 3 3 1 3 5 1 1 1 1 1 3 3 3 3 48
Herring gull
_(L. argentatus)_ 1 3 1 3 1 3 1 3 1 3 1 1 1 1 1 1 3 3 3 3 38
Thayer's gull _(L. thayeri)_ 3 3 5 3 1 3 1 3 1 3 1 1 1 1 1 1 3 1 3 3 42
California gull
_(L. californicus)_ 3 5 3 3 1 3 3 3 1 3 1 1 1 1 1 1 1 1 1 1 38
Ring-billed gull
_(L. delawarensis)_ 1 5 3 3 1 3 3 3 1 3 1 1 1 1 1 1 1 1 1 1 36
Mew gull _(L. canus)_ 1 5 3 3 1 3 3 3 1 3 1 1 1 1 1 1 3 3 3 3 44
Black-headed gull
_(L. ridibundus)_ 1 1
Franklin's gull
_(L. pipixcan)_ 1 1
Bonaparte's gull _(L.
philadelphia)_ 1 5 3 3 1 3 3 3 1 3 1 1 1 1 1 1 3 1 3 1 40
Heerman's gull _(L. 1 1
heermanni)_
Ivory gull _(Pagophila 1 5 3 5 3 3 3 3 1 3 1 3 0 1 1 1 1 1 1 3 43
eburnea)_
Black-legged kittiwake 1 3 3 5 1 3 3 3 1 3 5 3 0 1 1 1 3 3 3 3 49
_(Rissa tridactyla)_
Red-legged kittiwake _(R. 5 5 5 5 3 3 3 3 1 3 5 3 0 1 0 1 5 5 5 5 66
brevirostris)_
Ross' gull _(Rhodostethia 5 5 3 5 3 3 3 3 1 3 5 5 0 1 0 1 3 1 3 3 56
rosea)_
Sabine's gull _(Xema sabini)_ 3 3 3 5 1 3 3 3 1 3 1 3 0 1 1 1 3 3 3 0 44
Common tern _(Sterna 1 1
hirundo)_
Arctic tern _(S. paradisaea)_ 1 1 1 3 1 3 3 3 1 3 1 1 0 1 1 1 3 1 3 0 32
Aleutian tern _(S. aleutica)_ 5 3 3 5 3 3 3 3 1 3 1 1 0 1 1 1 5 5 5 1 53
Caspian tern _(Hydroprogne 1 1
caspia)_
Black tern _(Chlidonias 1 1
niger)_
Alcidae
Common murre _(Uria aalge)_ 1 5 3 5 1 5 5 5 5 5 5 3 1 1 3 5 3 3 3 3 70
Thick-billed murre _(U. 1 5 3 5 1 5 5 5 5 5 5 3 1 1 3 5 3 3 3 3 70
lomvia)_
Dovekie _(Plautus alle)_ 1 1
Black guillemot _(Cepphus 1 5 3 5 3 5 5 5 5 3 5 5 1 1 1 5 3 3 3 3 70
grylle)_
Pigeon guillemot _(C. 5 5 3 5 3 5 5 5 5 3 5 5 1 1 3 5 5 5 5 3 82
columba)_
Marbled murrelet 5 5 3 5 1 5 5 5 5 3 5 5 1 3 3 5 5 5 5 5 84
_(Brachyramphus marmoratus)_
Kittlitz's murrelet _(B. 5 5 5 5 1 5 5 5 5 5 5 5 1 3 3 5 5 5 5 5 88
brevirostris)_
Xantus' murrelet 1 1
_(Endomychura hypoleuca)_
Ancient murrelet 3 3 3 5 1 5 5 5 5 5 5 5 1 3 3 5 3 3 3 3 74
_(Synthliboramphus antiquus)_
Cassin's auklet 5 3 5 5 1 5 5 5 5 5 5 5 1 3 3 5 5 5 5 3 84
_(Ptychoramphus aleutica)_
Parakeet auklet 3 3 3 5 1 5 5 5 5 5 5 5 1 3 3 5 5 5 5 3 80
_(Cyclorrhynchus psittacula)_
Crested auklet _(Aethia 3 3 3 5 1 5 5 5 5 5 5 5 1 3 1 5 5 3 5 3 76
cristatella)_
Least auklet _(A. pusilla)_ 3 3 3 5 1 5 5 5 5 5 5 5 1 3 3 5 5 5 5 3 80
Whiskered auklet _(A. 5 5 5 5 1 5 5 5 5 5 5 5 1 3 3 5 5 5 5 5 88
pygmaea)_
Rhinoceros auklet 3 3 3 5 1 5 5 5 5 5 5 5 1 3 3 5 3 3 3 3 74
_(Cerorhinca monocerata)_
Horned puffin _(Fratercula 3 5 3 5 1 5 5 5 5 3 5 5 1 3 1 5 3 3 3 3 72
corniculata)_
Tufted puffin _(Lunda 3 5 3 5 1 5 5 5 5 3 5 5 1 3 1 5 3 3 3 3 72
cirrhata)_
Alcedinidae
Belted kingfisher 1 1 3 1 1 1 1 5 1 0 1 3 0 3 1 1 1 1 1 1 28
_(Megaceryle alcyon)_
Corvidae
Common raven _(Corvus corax)_ 1 1 1 1 1 1 1 1 1 0 1 1 3 1 1 1 1 1 1 1 21
Northwestern crow _(C. 3 5 3 3 1 1 1 1 1 0 1 3 1 1 1 1 5 5 5 5 47
caurinus)_
Table 2. _Criteria and points used in calculating Oil
Vulnerability Index._
Point assignment
1 3 5
Range
Breeding Large Medium Small
Migration Long Medium Short
Winter Large Medium Small
Marine orientation Coastal zone Intertidal Open water
Population
Size Large Medium Small
Productivity Large Medium Small
Habits
Roosting Shore Drift Water
Foraging Walking Flying Swimming
Escape Leave area Fly Dive
Flocking Small Medium Large
Nesting density Low Medium High
Specialization Low Medium High
Mortality
Hunted by man Low Medium High
Animal depredations Low Medium High
Non-oil pollution Low Medium High
History of oiling Low Medium High
Exposure
Spring Low Medium High
Summer Low Medium High
Fall Low Medium High
Winter Low Medium High
With these points in mind it is immediately obvious that Southeast
Alaska (Table 4), which has only 9 high-score birds, offers far less
potential for bird problems than does the Aleutian area (Table 5),
which has 24 high-score species. The planning agency could make some
immediate decisions on site priorities and research funding based on
such information.
Discussion
We are convinced that the OVI principle expressed here will become a
useful management tool with all sorts of possible applications. We
recognize some difficulties with the present version, but believe it
is timely to present the system so that a broader range of thought,
improvements, and application can be applied to it.
Of prime importance is the system's simplicity. The use of four levels
of value for each factor, instead of five or more, is an attempt to
simplify. Ian McHarg (1969) has shown that extremely complex land-use
values can be graphically compared and displayed by using three levels
in a way that is useful to decision makers. The difficulty of using
more levels of value was indicated by Sparrowe and Wight (1975) who
used up to 10 levels, enormously complicating the problem of dealing
with low-quality information, which is often all that is available.
The use of scores of 0, 1, 3, 5 instead of 0, 1, 2, 3 for 20 factors
enabled us to use the convenient 100 points instead of 60 points as the
maximum potential total score for any species.
The 20 factors that were evaluated are admittedly arbitrary; with
refinement and more detailed data they could be adjusted to show better
separation between affected species. The decision to use 20 factors
instead of more or less again relates to simplicity. This appears to be
the minimum number that will assure species separation and that can be
neatly displayed.
Table 3. _Oil Vulnerability Index (OVI) for families of birds
of the Northeast Pacific marine habitats, excluding rare and
endangered species in the scoring._
OVI per species
Number of Total
Family species OVI Average Range
Loons--Gaviidae 4 219 55 47-65
Grebes--Podicipedidae 3 148 49 44-56
Albatrosses--Diomedeidae 2 102 51 50-52
Shearwaters--Procellaridae 4 208 52 47-57
Storm-petrels--Hydrobatidae 2 130 65 63-67
Cormorants--Phalacrocoracid 4 235 59 52-63
Herons--Ardeidae 1 29 29 29
Waterfowl--Anatidae 33 1,765 53 32-78
Eagles and Hawks--Accipitridae 2 77 39 19-58
Ospreys--Pandionidae 1 37 37 37
Falcons--Falconidae 1 41 41 41
Cranes--Gruidae 1 24 24 24
Rails and Coots--Rallidae 1 33 33 33
Oystercatchers--Haematopodidae 1 65 65 65
Plovers--Charadriidae 7 287 41 26-57
Sandpipers--Scolopacidae 22 857 39 24-59
Phalaropes--Phalaropodidae 2 120 60 58-62
Jaegers and Skuas--Stercorariidae 3 123 41 39-43
Gulls and Terns--Laridae 16 730 46 32-66
Auks--Alcidae 15 1,164 78 70-88
Kingfishers--Alcedinidae 1 28 28 28
Crows--Corvidae 2 68 34 21-47
Total and Mean 128 6,490 51 19-88
The system will be much more useful when it is expanded to the
subspecific level. Many Holarctic species are represented in the
Northeast Pacific by a single race that would have a much higher OVI
than the species as a whole. For example, the OVI for the Peale's
peregrine falcon _(Falco peregrinus pealei)_ confined to marine
habitats within the Pacific region would be high; and the endangered
Aleutian Canada goose _(Branta canadensis leucopareia)_ would score 100
points instead of the 34 we show for Canada geese _(B. c.)_. If Tables
4 and 5 showed subspecies, the differences in value would be more
marked.
Tables 4 and 5 are for broad geographical areas. A comparison between
smaller areas would probably show more dramatic differences.
Because the dearth of easily available, applicable information
poses a problem in evaluating the various factors, our scoring was
conservative. Experts on the various avian families can doubtless
refine the scoring. If this system proves useful, investigators will
begin to acquire the information needed for more precise evaluations.
Ultimate perfection may never be achieved; however, as with the field
guides, the fact of minor professional disagreement should not destroy
the system's utility.
We believe re-scoring of all birds on the basis of various projects
should be avoided because a standard against which individual projects
can be measured is needed. If everyone did their own scoring, there
would be no standard, and projects evaluated by different investigators
would not be comparable. If a species list for the project area and
standard point scores are used, the level of involvement for many
species and perhaps for most species will be properly identified. As
with any system, there will be exceptions and the assessor will need
to deal with these as appropriate. The result will still be to focus
attention on those species and impacting factors where it is most
needed.
Table 4. _Oil Vulnerability Index for 109 species of birds of
Southeast Alaska (Total Points--2,678)._
OVI 1-20 OVI 21-40 OVI 41-60
Marsh hawk 19 Great blue heron 29 Common loon 47
52 species, rare Canada goose 34 Arctic loon 58
or occasional
(one point each) 52 White-fronted goose 36 Red-throated loon 49
Snow goose 32 Red-necked grebe 44
Mallard 36 Horned grebe 48
Pintail 36 Whistling swan 50
Green-winged teal 34 Trumpeter swan 63
American wigeon 36 Greater scaup 52
Semipalmated plover 28 Lesser scaup 52
Killdeer 26 Common goldeneye 48
Common snipe 29 Barrow's goldeneye 56
Spotted sandpiper 24 Bufflehead 52
Greater yellowlegs 30 Harlequin duck 60
Lesser yellowlegs 30 Common merganser 56
Pectoral sandpiper 32 Red-breasted merganser 56
Least sandpiper 34 Bald eagle 58
Herring gull 38 Peregrine falcon 41
Bonaparte's gull 40 Black turnstone 57
Arctic tern 32 Rock sandpiper 59
Belted kingfisher 28 Dunlin 41
Common raven 21 Short-billed dowitcher 41
Western sandpiper 47
Glaucous-winged gull 56
Thayer's gull 42
Mew gull 44
Northwestern crow 47
Totals 71 665 1,324
OVI 61-80 OVI 81-100