REPRODUCTIVE-BEHAVIOR OF HATCHERY AND WILD COHO SALMON (ONCORHYNCHUS-KISUTCH) - DOES IT DIFFER

We report an experimental study that contrasts the reproductive behavior of wild to hatchery coho salmon (Oncorhynchus kisutch). The hatchery fish had completed four generations of sea-ranching, which involves artificial breeding and juvenile rearing but natural growth to adulthood in the sea. Mature males and females were individually tagged, measured and placed into three experimental arenas in a stream channel. One arena contained isolated pairs of fish, thus providing data on reproductive behavior in the absence of competition. A second arena contained male and female hatchery fish and a third arena contained male and female wild fish. In the latter two arenas the fish were free to compete among themselves for breeding opportunities. Three variables significantly influenced reproductive behavior and breeding sucess: (1) competition; (2) body weight; and (3) hatchery versus wild origin. In the absence of competition, both hatchery and wild fish bred readily. However, competition delayed spawning, reduced nest numbers, increased body wounding, increased egg loss through retention and nest superimposition, and increased variance in breeding success. Body weight was an important determinant of success in the competitive environment. Small females were delayed in spawning and experienced greater egg losses, and small males had reduced access to spawning females. As a group, the hatchery fish differed from the wild fish in breeding behavior and potential. Hatchery females had larger egg masses but smaller fecundities than wild females due to their larger egg size. Hatchery males had larger testes than wild males, but were less aggressive, exhibited less spawning behavior and were generally less active than wild males. These results imply significant differences in the reproductive potential of hatchery relative to wild fish during competition.