Body size, arrival date, and reproductive success of pink salmon, Oncorhynchus gorbuscha

Abstract

The influences of adult body size on breeding opportunity and progeny survival are widely recognized in many animals but the timing of reproduction may also be very important. Specifically, the benefits of large size may be offset by selective mortality, and dominance may be related to competition and opportunity; all of these factors may be related to date as well as size. The relative influences of size and breeding date on reproductive success were investigated in a naturally reproducing population of pink salmon (Oncorhynchus gorbuscha), an anadromous, semelparous fish species, in southeast Alaska during the 1997– 2000 breeding seasons. Females showed strong positive relationships between body size and both fecundity and egg size, with a trade off between these traits. Duration of nest defense was associated with entry date (early arrivals lived longer) and bear predation, which also affected the proportion of females completing egg deposition. In males, access to reproductively active females was positively influenced by body size but arrival date favored large males early in the season and small males late in the season. The reproductive life span of males was reduced by bear predation but not influenced by body size or arrival timing. Taken together, the results indicated that both body size and arrival date affect potential reproductive success but complex interactions between these factors and predation are also very important.