Fish Populations, Following a Drought, in the Neosho and Marais des Cygnes Rivers of Kansas

by James E. Deacon

Ictalurus punctatus (Rafinesque)
Channel Catfish

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.