Optimal age at sexual maturity of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr

Reproductive potentials of transplanted curthroat trout (Salmo clarki) and Dolly Varden charr (Salvelinus malma) and of their donor stocks were estimated from life history data. We found good agreement between observed and predicted age at maturity in all populations, and cannot reject the hypothesis that the fish matured at the age maximizing the overall lifetime reproductive potential ( \(\Delta \mu _{\iota } = 0 = In \left( {{{a_i^p } \mathord{\left/ {\vphantom {{a_i^p } {a_i^L }}} \right. \kern-0em} {a_i^L }}} \right) + A_i + {{B_i } \mathord{\left/ {\vphantom {{B_i } T}} \right. \kern-0em} T}\) ). Our estimates were insensitive to probable variations in female fecundity, adult mortalityrate and maximum body length. Small changes in either juvenile mortality-rate or individual growth-rate had marked effects on the estimations, as did changes in the Malthusian parameter (r). Three alternative mechanistic explanations of how age at maturity is determined could be rejected. We suggest that fish are able to adjust the maturity age non-genetically to changes in growth-rate, and that temporal variations in juvenile survival-rate allow coexistence of genotypes coding for different ages at maturity at the same growth-rate.