Effects of First-time Spawners on Stock-recruitment Relationships for Two Groundfish Species

Abstract

Recent experimental studies suggest that first-time spawning fish may not be as reproductively fit as repeat spawners. Traditional stock-recruitment models consider all mature fish as equivalent contributors to the spawning stock biomass. In this study we examine the effects of discounting first-time spawners on the stock-recruitment relationship of two species with varying life histories: Georges Bank haddock (Melanogrammus aeglefinus), a fast maturing gadoid, and Gulf of Maine witch flounder (Glyptocephalus cynoglossus), a slow maturing pleuronectid. Proportions of first-time spawning haddock ranged from 3 to 62 percent of the spawning stock biomass during 1963-96. Exclusion of all first-time spawners from spawning stock biomass improved the Ricker stock-recruitment relationship by 39 percent. For witch flounder, proportions of first-time spawners were less variable, never exceeding about 30 percent. Adjusting the spawning stock biomass for first-time spawners did not improved the overall relationship for witch flounder.