The flathead is the largest sport-fish occurring in Kansas. Several
weighing more than 40 pounds are caught from streams each year, and the
species reportedly attains sizes in excess of one hundred pounds.
Several aspects of the biology of the flathead in Kansas have been
discussed by Minckley and Deacon (1959).
The abundance of flathead declined slightly from 1957 through 1959,
counting fish of all sizes. This trend is attributable to a large hatch
in 1957; the 1957 year-class strongly dominated the population
throughout my study. Natural mortality in that year-class was
compensated by increased average size of the individuals (to six inches
in autumn, 1958, and 11 inches in autumn, 1959).
The numbers of flathead caught at the upper stations on the Neosho and
Marais des Cygnes rivers differed from the general trend in that the
species was rare in 1957 and increased slightly by 1959. Flathead are
most numerous in large streams, and in the drought they probably were
almost extirpated from the headwaters. After 1957, continuous flow and
increased volume of flow were accompanied by a gradual increase in
numbers of flathead in the upstream parts of the two rivers. The species
was most abundant at the middle and lower Neosho stations, where 10.5
per cent of all fish shocked in 1957 and 1958 were _P. olivaris_.
The habitat of the flathead varied with size of the individuals.
Young-of-the-year inhabited swift riffles having rubble bottom;
individuals four to 12 inches in total length were distributed
throughout the stream; those more than 12 inches in total length were
most commonly in pools in association with cover (rocks, or drifts of
fallen timber).
Male flathead mature at 15 to 18 inches total length, females at 18 to
20 inches. The spawning season in 1959 probably began in early June and
extended to mid-July. I attempted to find spawning fish on 19 June and
for one month thereafter. On 19 June nine holes were dug into a 75-yard
section of a clay bank adjacent to a long, shallow, rubble riffle.
A flathead was first found in one of these holes on 22 June, and
others were frequently found in this and one other hole until mid-July.
Although channel catfish were often found in nearby holes, that
species was never present in the two holes used by flatheads. The
holes occupied by flathead (as well as those used by channel catfish)
characteristically had silt-free gravel bottoms and a ridge of clean
gravel across the entrance.
A nest containing a flathead and eggs was located on 11 July. In
checking the hole I first put my foot into the entrance, then slowly
advanced my hand into the hole, feeling along the bottom with my fingers
until they entered the open mouth of a large catfish. I backed off
slowly and then felt beneath the fish. The fish was directly above the
egg-mass, seemingly touching the eggs with its belly. As I touched the
front of the egg-mass the fish struck viciously, taking my entire fist
into its mouth. It continued striking until I removed my hand from the
hole after obtaining a small sample of eggs, which proved to be in an
early stage of development (no vascularization evident).
When the nest was checked again on 13 July the eggs and fish were gone.
As in the case of channel catfish, I suspect that disturbance of a
flathead in the early stages of guarding the nest results in destruction
of the nest either by the guardian fish or by predation resulting from
its absence.
The hole occupied by the above fish was one that I had dug seven to nine
inches in diameter and extending two and one-half to three feet into the
bank. At the time this fish occupied the hole its depth was
approximately the same as originally, but the entrance had been enlarged
to 14 inches in diameter, and the chamber widened to 32 inches. The
holes were checked later in the summer and all were heavily silted or
had been undercut by action of the current.
The number of flathead of catchable size was not reduced as severely
during my study as was the number of large channel catfish. Flathead
have a longer life-span than channel catfish; therefore, it is not
surprising that, of flathead and channel catfish that survived the
drought, a higher proportion of flathead persisted throughout the next
three years, in which my study was made. In drought, when fish were
concentrated in residual pools, the piscivorous (fish eating) habit of
flatheads may have favored their survival.
The growth rate of flathead taken from the Neosho River in 1957 and 1958
was reported by Minckley and Deacon (1959:351-352). Individuals hatched
in 1955 and 1956 and collected in 1957 had attained average sizes of 9.5
inches and 4.8 inches, respectively, by the end of the 1956
growing-season.
Flatheads of the 1956 and 1957 year-classes attained average sizes of
8.7 and 3.2 inches, respectively, by the end of the 1957 growing season.
These data indicate that growth was retarded in the summer of 1957. Many
species, including _P. olivaris_, had an exceptionally large hatch in
1957, associated with increased water levels in that year. Despite the
great increase in amount of water, I suppose that young-of-the-year and
yearlings were subjected to crowding resulting from exceptional hatches.
This caused reduction in growth of young flathead, and probably in
several other species.
Food of flatheads 4.0 inches and shorter was nearly all insect larvae;
that of fish 4.1 to 10 inches was insect larvae, fishes and crayfish;
and that of larger flatheads was mostly fish and crayfish. The specific
kind of food eaten was correlated with abundance of the food item in the
stream (Minckley and Deacon, 1959:350-351).
#Noturus flavus# Rafinesque