Relationship between size and condition metrics and the recapture probability of stocked landlocked Atlantic salmon and brown trout in lake fisheries

Stocking-derived catches serve as indicators of the feasibility of put-grow-and-take (PGT) fisheries for salmonids. Here, we report results from a large tagging program of landlocked Atlantic salmon and brown trout stocked at ages 2 and 3 in two large geographically close boreal lakes, Pielinen and Höytiäinen, in Finland. In addition to describing recapture patterns in these lake fisheries, we assessed whether the commonly measured phenotypic characters such as body length and condition, fin erosions, and early male maturity, were related to recapture probabilities. In both species and study lakes, the released fish recruited to fisheries at 3 or 4 years of age and were exposed to heavy total mortality rate (Z = 1.06 – 2.07 yr⁻¹) as estimated from catch curves. As in many previous studies, a positive relationship was found between fish length at release and recapture probability. Together with the influence of body condition, the effect of body length was particularly strong among fish stocked at age 2. In both species, recapture probability was lower for fish that showed precocious maturity and negatively associated with pectoral fin erosion. Our results complement existing knowledge on the relationship between fish condition indicators and stocking success, and provide data to set quality metrics for fish released for PGT purposes. The recapture patterns underline the role and responsibility of fisheries management in reducing the premature harvest of stocked fish to ensure positive net yields from the stocking programs and decreasing the overall mortality rate to reach conservation goals.