Secondary sexual characters, energy use, senescence, and the cost of reproduction in sockeye salmon

Reproductive development and energy stores were characterized for sockeye s almon (Oncorhynchus nerka) maturing in the wild (Pick Creek, Bristol Bay, A laska). Between freshwater entry and the start of spawning, ovaries increas ed in mass by 87.1% and secondary sexual characters increased in linear dim ension by 13.0-47.4%. Between the start of spawning and death, secondary se xual characters decreased in relative size by 3.3-12.7%. Mass-specific soma tic energy declined from freshwater entry (6.7% fat, 20.6% protein, 6.6 kJ. g(-1)) to the start of spawning (1.6% fat, 18.0% protein, 4.5 kJ.g(-1)) and finally to death (0.1% fat, 14.4% protein, 2.9 kJ.g(-1)). Stored fat appea red to be used primarily for upriver migration and egg production, whereas stored protein appeared to be used primarily for the development of seconda ry sexual characters and metabolism during spawning. Most development of se condary sexual characters occurred late in maturation, perhaps to forestall deterioration of muscle tissue. Relative to populations with long freshwat er migrations, Bristol Bay sockeye salmon stored less fat before entering f resh water and used less fat before death. The total energy cost of reprodu ction (freshwater entry until death, including gonad investment) was 74.1% for females and 66.1% for males, higher than levels typically reported for iteroparous salmonids.