Читать книгу Fish Populations, Following a Drought, in the Neosho and Marais des Cygnes Rivers of Kansas - James E. Deacon - Страница 20

Location	Date	Number	Average total length (inches)	Range
Middle Neosho	1957	19	22.2	14-32
Middle Neosho	1958	57	22.2	14-40
Middle Neosho	1959	64	21.6	13-43
Lower Neosho	1957	14	29.4	9-45
Lower Neosho	1958	7	25.3	23-28
Lower Neosho	1959	107	26.2	16-43

Because collecting was intensive and several methods were used, I think that the population of gars was sampled adequately. Wallen (Fishes of the Verdigris River in Oklahoma, 1958:29 [mimeographed copy of dissertation, Oklahoma State University]) took large individuals in the mainstream of the Verdigris River in Oklahoma and small specimens from the headwaters of some tributaries. Because I took young-of-the-year at the lower Neosho station, it is possible that long-nosed gar move upstream when small and then slowly downstream to the larger parts of rivers as the fish increase in size. This pattern of size-segregation, according to size of river, merits further investigation.

Ripe, spent, and immature long-nosed gar (38 males and 10 females) were taken in three gill nets, set across the channel, 150 to 500 yards below a riffle, at the lower Neosho station on June 16, 17, and 18, 1959. On 23 June, 1959, 12 males and two females were taken in gill nets set 50, 150, and 400 yards above the same riffle. Operations with the shocker between 24 June and 10 July, 1959, yielded 29 males and three females. The fish were taken from many kinds of habitat in a three-mile section of the river.

Direction of movement as recorded from gill nets shows that of 67 gar taken, 45 had moved downstream and 22 upstream into the nets. Only ten of the above gar were taken from the nets set above the riffle; six of the ten were captured as they moved downstream into the nets.

On one occasion I watched minnows swimming frantically about, jumping out of the water, and crowding against the shore, presumably to avoid a long-nosed gar that swam slowly in and out of view. I have observed similar activity when gar fed in aquaria. Stomachs of a few gar from the Neosho River were examined and found to contain minnows and some channel catfish.

Long-nosed gar have a relatively long life span (Breder, 1936). This longevity and their ability to gulp air probably insure excellent survival through periods of adverse conditions. The population of long-nosed gar probably would not be drastically affected even in the event of a nearly complete failure of one or two successive hatches. Maturity is attained at approximately 20 inches, total length.

Collections at the middle Neosho station in 1958 indicate that the long-nosed gar is more susceptible to capture at night than in daytime (Table 9, p. 402).

Lepisosteus platostomus Rafinesque Short-nosed Gar

Only one short-nosed gar was taken in 1957, at the lower station on the Neosho River. In 1958 this species was taken at the lower station on the Marais des Cygnes and in 1958 and 1959 at the lower and middle stations on the Neosho. More common in the Neosho than the Marais des Cygnes, L. platostomus occurs mainly in large streams and never was taken in the upper portions of either river. Although short-nosed gar were about equally abundant at the middle and lower stations on the Neosho, the average size was greater at the lower station (Table 6). This kind of segregation by size is shared with long-nosed gar, and was considered in the discussion of that species. Short-nosed gar were taken only in quiet water. Both species were collected most efficiently by means of gill nets and shocker. While shocking, I saw many gar only momentarily, as they appeared at the surface, and specific identification was impossible. The total of all gar seen while shocking indicated that gar increased in abundance from 1957 to 1959 (see Tables 5 and 6). Judging from the gar that were identified, the increase was more pronounced in short-nosed gar than in long-nosed gar.

At the lower Neosho station in 1959, two ripe females and one spent female were taken in gill nets (16, 23 and 17 June, respectively) and were moving downstream when caught. No males were taken in the nets. Subsequently, by means of the shocker (26 June-8 July), two spent and two ripe males were captured in quiet water of the mainstream that closely resembled areas in which the gill nets were set. No females were taken by means of the shocker.