Spawning success of males using alternative mating tactics in sockeye salmon, Oncorhynchus nerka

Abstract

Protein electrophoresis was used to determine the relative spawning success of jack sockeye salmon, Oncorhynchus nerka, males when they joined spawnings of larger, older individuals in experimental enclosures in the natal stream, Pierre Creek, Babine Lake, British Columbia. We attempted to relate the results to distance of the jack from female before spawning and relative size of the jack to the alpha male. Further, we measured the relationships between relative gonad size and available sperm volume to body size to determine if sperm competition could also play a role in determining the relative spawning success of males. Jack spawning success was variable (3-93%) and not significantly different from that of large males, even though they were further from the female before spawning, had smaller gonads, and had less available sperm. Jack males were adept at sneaking, usually commencing spawning within a split second of the alpha male and always on the opposite, free, side of the spawning female. The results are related to various theories on the evolution of alternative mating strategies and tactics in Pacific salmon.