Use of fish production per unit biomass ratios for measuring the productive capacity of fish habitats

Species-specific production rate per unit biomass (P/B, per year) ratios were calculated for 79 freshwater fish species of eastern Canada. P/B (per year) ratios were calculated using two methods, which were based on allometry with fish weight-at-maturity and life expectancy, respectively. P/B (per year) values obtained by the two methods were significantly correlated, as expected from life history theory, since the two predictors (longevity, size-at-maturity) were themselves correlated. Species-specific P/B (per year) ratios were also significantly correlated with field observations of P/B from published sources. The estimation of P/B based on allometry with fish size is recommended because of its utility; the predictive equation is P/B (per year) = 2.64W(mat)(-0.35), where W-mat is weight-at-maturity. Both the coefficient 2.64 and the exponent -0.35 of this equation are provisional and require further validation from field studies of fish production. More accurate estimates of P/B are possible if population-specific information on size-at-maturity or mean size is known. The product of average fish biomass and estimated P/B coefficients (habitat productivity index (HPI) = B x P/B) is a proposed measure of habitat productive capacity.