Cost-Benefit Analysis of Combining Genetic Markers and Otolith Chemistry to Track the Fate of Hatchery-Reared Fish

Hatchery programs have been developed to offset fishery declines.  However, in only a few systems have researchers been able to effectively assess the efficacy of such programs.  We have taken a unique approach to compare and combine genetic and otolith chemistry analyses to track the fate of hatchery-reared fish in the wild.  In Texas, one of the top recreational fishes is the spotted seatrout (Cynoscion nebulosus).  Three hatcheries stock fingerlings on a regional basis.  Since managers are interested in the efficacy of their release programs, we are using spotted seatrout as a model species to examine the best methods or combination of methods to cost-effectively estimate the contribution of hatchery-reared fish to wild populations.  We collected otoliths and fin clips from juvenile fish from four wild populations as well as the three hatcheries over several years.  DNA from 2007 brood stock was also collected for genetic analyses.  We examined chemical signatures in otoliths for location specific tags by measuring concentrations of two stable isotopes (δ¹³C and δ¹⁸O) and several trace elements and performing discriminant function analysis.  Juveniles and brood stock from 2007 were also genotyped with two types genetic markers (10 microsatellite loci and ND4 sequence), and the resulting data was subjected to parentage analysis. Both analyses can identify hatchery fish and increasing information increases the discrimination of fish origin.  For example, adding trace element chemistry to the stable isotope analysis increases overall discrimination from 73% to 92%.   We are using “blind” random pulls from this data set to assess the costs and benefits of each approach alone and in combination.  Our results will provide fisheries managers with recommendations for cost effective methods for estimating the efficacy of their stock enhancement programs.