ALLOMETRY OF MARINE MORTALITY OF PACIFIC SALMON

Rearing experiments have shown that instantaneous growth rate, G (d(-1 )), of juvenile salmonids scales with body weight, W (g), as G = aW(-b ), where b has an average value of 0.37. Research on nonsalmonid fishe s has shown that instantaneous natural marine mortality rate, M (d(-1) ), also scales with body weight as M = cW(-x), where x has an average value of 0.37. Therefore, if b - x similar to 0, then c < a. These two hypotheses were tested for Pacific salmon with data on smelt-adult su rvival, s, smelt weight, W-0 (g), and adult weight, W (g), taken from the scientific literature. A nonlinear regression of survival on weigh t was developed, on the basis of allometric marine growth: log(e)(s) = -(alpha/beta)(W-beta - W-0(beta)), where alpha = c/a and beta = b - x . The regression model explained 33% of the variance in mean log(e)(s) of sockeye salmon (Oncorhynchus nerka) with parameter values (+/- 1SD ) of alpha = 0.226 +/- 1.171 and beta = 0.120 +/- 0.990. The model exp lained 68% of the variance in the pooled mean log(e)(s) of pink (O. go rbuscha), chum (O. Keta), coho (O. Kisutch), and sockeye salmon, as we ll as steelhead trout (O. mykiss), with parameter values (+/- 1SD) of alpha = 0.528 +/- 0.490 and beta = -0.053 +/- 0.221. The near-zero est imates of beta and the fractional estimates of alpha support the hypot hesis that x similar to 0.37 and c < a. Therefore, the best estimate o f M for Pacific salmon is M = 0.528aW(-0.37), or, since a = G/W--0.37, M = 0.528G. These survival-size and mortality-size relationships may be used to make preliminary estimates of survival and mortality for wi ld populations of Pacific salmon.