The abundance of channel catfish was greatly reduced as a result of the
drought of 1952-1956. With the resumption of normal stream-flow in 1957,
the small numbers of adult channel catfish present in the stream
produced unusually large numbers of young. These young of the 1957
year-class, which reached an average size of about nine inches by
September 1959, will provide an abundant adult population for several
years.
The reduction in number of channel catfish in streams can be related to
the changed environment in the drought. When stream levels were low in
1953 (Tables 1-4), fish-populations were crowded into a greatly reduced
area. An example of these crowded conditions was observed by Roy
Schoonover, Biologist of the Kansas Forestry, Fish and Game Commission,
in October, 1953, when he was called to rescue fish near Iola, Kansas.
The Neosho River had ceased to flow and a pool (less than one acre)
below the city overflow dam was pumped dry. Schoonover (personal
communication) estimated that 40,000 fish of all kinds were present in
the pool. About 30,000 of these were channel catfish, two inches to 14
inches long, with a few larger ones. Fish were removed in the belief
that sustained intermittency in the winter of 1953-1954 would result in
severe winterkill. These conditions almost certainly were prevalent
throughout the basin.
In addition to winterkill, crowding probably resulted in a reduced rate
of reproduction by channel catfish, and by other species as well. This
kind of density-dependent reduction of fecundity is known for many
species of animals (Lack, 1954, ch. 7). In fish, it is probably
expressed by complete failure of many individuals to spawn, coupled with
scant survival of young produced by the adults that do spawn.
Reproductive failure of channel catfish in farm ponds, especially in
clear ponds, is well known, and is often attributed to a paucity of
suitable nest-sites (Marzolf, 1957:22; Davis, 1959:10).
In the Neosho and Marais des Cygnes rivers, the intermittent conditions
prevalent in the drought resulted in reduced turbidity in the remaining
pools. Many spawning sites normally used by channel catfish were
exposed, and others were rendered unsuitable because of the increased
clarity of the water. In addition, predation on young channel catfish is
increased in clear water (Marzolf; Davis, _loc. cit._), and would of
course be especially pronounced in crowded conditions. The population
was thereby reduced to correspond to the carrying capacity of each pool
in the stream bed.
The return of normal flow in 1957 left large areas unoccupied by fish
and the processes described above were reversed. The expanded habitat
favored spawning by nearly the entire adult population, and conditions
for survival of young were excellent. As a result, a large hatch
occurred in the summer of 1957. (Several hundred small channel catfish
were sometimes taken by use of the shocker a short distance upstream
from a 25-foot seine, set in a riffle). Subsequent survival of the 1957
year-class has been good. By 1959, few of the catfish spawned in 1957
had grown large enough to contribute to the sport fishery, but they are
expected to do so in 1960 and 1961.
The 1957 year-class was probably the first strong year-class of channel
catfish since 1952. Davis (1959:15) found that channel catfish in Kansas
seldom live longer than seven years. The 1952 year-class reached age
seven in 1959. The extreme environmental conditions to which these fish
were subjected in drought caused a higher mortality than would occur in
normal times. The adult population in the two rivers probably was
progressively reduced throughout the drought, and the reduction will
continue until the strong 1957 year-class replenishes it. For these
reasons, fishing success was poor in 1957-1959.
Juvenile channel catfish were more abundant in the Neosho than in the
Marais des Cygnes in 1958 and 1959, although both streams supported
sizable populations. In the Marais des Cygnes the upper station had
fewer channel catfish than the middle and lower stations. In the Neosho,
populations were equally abundant both upstream and downstream. The
habitat of channel catfish in streams has been discussed by Bailey and
Harrison (1948).
I found adults in various habitats throughout the stream, but most
abundantly in moderately fast water at the lower and middle Neosho
stations. At the upper Neosho station where riffles are shallow,
yearlings and two-year-olds were numerous in many of the small pools
over rubble-gravel bottom. Cover was utilized where present, but large
numbers were taken in pools devoid of cover. Young-of-the-year were
nearly always taken from rubble- or gravel-riffles having moderate to
fast current at both upstream and downstream stations.
Collections showed that young of 1957 were abundant on riffles
throughout the summer and until 17 November, 1957. Subsequent
collections were not made until 11 May, 1958, at which time 1957-class
fish still were abundant on riffles at the lower Neosho station; on that
date, the larger individuals were in deeper parts of the riffles than
were smaller representatives of the same year-class.
In a later collection (2 June, 1958), numbers present on the riffles
were greatly reduced and the larger individuals were almost entirely
missing. Some of the smaller individuals were still present in the
shallower riffle areas. Table 7 compares sizes of the individuals
obtained on 2 June with sizes collected from deep riffles at the middle
Neosho station on 7 June, 1958. The larger size of the group present in
deep riffles is readily apparent. The yearlings almost completely
disappeared from subsequent collections on riffles.
A bimodal size-distribution of young-of-the-year was noted also in 1958
and 1959; but, no segregation of the two sizes occurred on riffles in
summer. Marzolf (1957:25) recorded two peaks in spawning activity in
Missouri ponds. Two spawning periods may account for the bimodal size
distribution of young-of-the-year observed in my study.
In 1959, young-of-the-year began to appear in the latter part of June
and became abundant by the first part of July. Individuals as small as
one inch T. L. were taken in gravel-bottomed riffles on 1 July, 1959.
Yearling individuals at the lower and middle Neosho stations showed a
pronounced tendency to move into shallow, moderately fast water over
rubble or gravel bottom at night, where they were nearly ten times more
abundant than in daytime (Table 9). Adults probably have the same
pattern of daily movement as yearlings, except that at night the adults
move to deeper riffles. Bailey and Harrison (1948:135-136) demonstrated
that channel catfish feed most actively from sundown to midnight.
Channel catfish (especially two-year-olds and adults) were abundant on
a rubble-riffle during the day in some collections at the lower Neosho
station in 1959.
TABLE 7. LENGTH-FREQUENCY OF CHANNEL CATFISH FROM THE NEOSHO RIVER,
1957, 1958 AND 1959. (NUMBERS IN VERTICAL COLUMNS INDICATE THE
NUMBER OF INDIVIDUALS OF A CERTAIN SIZE COLLECTED ON THAT DATE.)
June 2 June 7
1958 1958
Length Nov. 2 (shallow (deep Sept. 9 Sept. 11
in inches 1957 riffle) riffle) 1958 1959
1.5 1
2.0 3
2.5 13 2 1 2
3.0 4 11 3 4
3.5 3 21 7 1 14
4.0 11 12 9
4.5 4 10 1
5.0 2 11 2
5.5 1 7 26
6.0 58 2
6.5 1 32 5
7.0 16 5
7.5 1 4 5
8.0 22
8.5 45
9.0 81
9.5 41
10.0 21
10.5 8
11.0 4
11.5 1
12.0 3
12.5 1
13.0 1
Near the end of the spawning season in 1959, I found spawning catfish at
the lower Neosho station. Ripe females were taken between 9 June and 30
June, 1959; and, on 19 June I found a channel catfish nest with eggs
(water temp. 79 deg. F.). The nest-site was a hole in the base of a clay
bank; the floor was clean gravel with a small mound of gravel at the
entrance. The nest-opening, five to six inches in diameter, widened
almost immediately into a chamber about two and one-half feet long and
one foot wide. Normally the water was about six inches deep in the
mainstream as it ran over a riffle adjacent to the catfish nest. When
I put my hand into the opening the fish bit vigorously, but became
quiescent when I stroked its belly. I then felt the rounded gelatinous
mass of eggs on the bottom of the nest. On June 22 (water temp. 86 deg. F.)
the fish was removed, struggling, from the nest, and returned to the
stream. The next day (23 June 1959, water temp. 84 deg. F.) the eggs had
hatched and the young were in a swarm in the nest. The adult did not
attempt to bite but left as soon as I put my hand into the hole.
Marzolf (1957:25) reports that young remain in the nest from seven to
eight days after hatching. My seining records show a marked increase in
abundance of small young-of-the-year on the first of July. Probably the
time of hatching of the nest described above correlated well with
hatches of other nests.
One and sometimes two channel catfish were found in other holes in
the stream-bank or bottom. The fish occasionally attacked my hand
vigorously, but at other times remained quiet or left without attacking.
No other channel catfish eggs were found, although one hole under a rock
in the middle of the river had one or two individuals in it each time it
was checked until 11 July, 1959. A local fisherman informed me of his
belief that these holes are occupied only in the spawning season.
Observations that I made in a pond owned by Dr. E. C. Bryan of Erie
indicated that channel catfish, when disturbed in the early stages of
guarding the eggs, either eat the eggs and abandon the nest or leave the
nest exposed to predation by other animals. In the later stages of
nesting, the fish, if removed, will return to guard the nest. After the
eggs hatch the guarding response probably diminishes and the fish leaves
the nest readily.
At the lower Neosho station, several "artificial" holes were dug into
the clay bank and two pieces of six-inch pipe were forced into the bank.
Nearly all these holes were occupied by catfish for a short period in
June; many of the holes were enlarged, either by the current or by fish.
I suspect that fish enlarged some holes, because in the spawning season
several males were observed that had large abrasions atop their heads,
around their lips, and to a lesser extent on their sides. These could
have been caused by butting and scraping the sides, roof and floor of a
hole. I found it possible to enlarge the holes by rapidly moving my hand
while it was inside a hole.
The growth-rate of channel catfish in the Neosho was approximately the
same at all stations, and the large 1957 year-class grew to an average
size of about nine inches by mid-September, 1959 (Table 7). Channel
catfish mature at a total length of 12 to 15 inches. Thus, most
individuals of the 1957 year-class in the Neosho River probably will
mature in their fourth or fifth summer (1960 or 1961 spawning season).
The sizes attained by young-of-the-year in 1957 differed in the two
rivers. Six hundred and thirty-three young taken in the Marais des
Cygnes River attained an average size of 4.7 inches (range two to six
inches) by mid-September. (Age was determined by length-frequency and
verified by examining cross-sections of fin-spines from the larger
individuals). One hundred and fifty young from the Neosho River averaged
3.0 inches (range 2 to 3.7 inches) on 2 November. Gross examination of
the riffle-insect faunas indicated a larger standing crop in the Neosho
than in the Marais des Cygnes River. Thus, the slower growth of young
channel catfish in the Neosho seemed not to be correlated with food
supply. Bailey and Harrison (1948:125-130) found that young channel
catfish in the Des Moines River, Iowa, fed almost exclusively on aquatic
insect larvae. My observations indicate that this is true in the Neosho
and Marais des Cygnes rivers also.
Young produced in 1958 in the Neosho River attained an average total
length of three inches by 26 August, and young produced in 1959 attained
an average size of 3.5 inches by 11 September. Both groups probably
continued growth until October, and may have averaged four inches total
length at that time.
The 1958 and 1959 year-classes were much less abundant than were the
1957 young. Therefore, it seems likely that the growth of the 1957 young
in the Neosho River was depressed because of crowding. The 1959
year-class was larger than the small 1958 year-class, thus conforming to
a general expectation that strong year-classes will be followed by weak
year-classes.
Reproduction by channel catfish in 1957 seemed greater in the Neosho
River than in the Marais des Cygnes River (Table 10); this coincided
with a greater change in volume of flow in the Neosho River than in the
Marais des Cygnes River (Tables 1-4). The 1957 year-class seemed more
crowded, and grew more slowly, in the Neosho than in the Marais des
Cygnes River.
#Ictalurus natalis# (LeSueur)