FACTORS AFFECTING THE DURATION OF NEST DEFENSE AND REPRODUCTIVE LIFE-SPAN OF FEMALE SOCKEYE-SALMON, ONCORHYNCHUS-NERKA

Reproductive success of female animals is often affected by a combinat ion of fecundity and parental care. In female salmonid fishes, acquisi tion of nest (redd) sites and prevention of their use by other females are critical to reproductive success. These factors are particularly important for stocks that spawn at high densities. Body size is positi vely correlated with fecundity and egg size, and has been hypothesized to control the outcome of intrasexual competition and longevity. We t ested this hypothesis by evaluating the influences of body size. intra sexual aggression and arrival date on duration and success of redd gua rding by female sockeye salmon, Oncorhynchus nerka, in a small Alaskan creek. Contrary to the hypothesis, larger females guarded their redds no longer than smaller females, and did not live as long in the strea m. Aggression was not related to body size or overall longevity but wa s positively correlated with residence period on the redd. Females tha t entered the creek earlier lived longer, spent longer on their redds, and spent more time guarding their redds after spawning than females that entered the creek later. However, despite their longevity, early- arriving fish were more likely to have their redds reused by another f emale because they died before all the females had selected redd sites . The small average body size in this stock is consistent with weak se lection for large size, and with our evidence that size provided littl e if any advantage in nest guarding.