Movement and population size of the river sculpin Cottus hangiongensis in the Daitobetsu River of southern Hokkaido
- Laboratory of Embryology and Genetics, Faculty of Fisheries, Hokkaido University, 041, Hakodate, Japan
Individual movements and population size of the amphidromous sculpinCottus hangiongensis, excluding young-of-the-year smaller than 50 mm in body length, were studied from October 1983 to December 1984 in 5 separate sections of the Daitobetsu River of southern Hokkaido, by using mark-recapture methods. During the non-breeding season, distinct inclinations in density, body length distribution and sex ratio ofC. hangiongensis populations were found along the course of the river. The population density was the highest, 3.45 per m2, in the lowest section and decreased in the upper sections. Larger males were found in larger numbers toward the lower reaches, whereas the sex ratio, which was biased in favor of females, was generally more striking upstream. These characteristics of the population structure may result from the amphidromous life history and the polygynous mating system of this species. Many marked fish were recaptured within the original sections, where they had been marked and released, throughout the year. During the non-breeding season, especially, the mean movement was 40.6 m, with the greatest movement being 92 m. During the breeding season, on the other hand, some sculpins appeared to move downstream before spawning and upstream after spawning. Such downstream spawning migration may increase the chance of encountering a mate, and for females it may enhance the chance of encountering larger males. Moreover, it may also contribute to a decrease in the mortality rate of their flowing larvae.
- 1 - sciences appliquees, technologies et medecines
- 2 - sciences biologiques et medicales
- 3 - sciences biologiques fondamentales et appliquees. psychologie
- 1 - Life Sciences ; 2 - Agricultural and Biological Sciences ; 3 - Ecology, Evolution, Behavior and Systematics