The Relative Influence of Age Structure, Predation, and Temperature on Stock-Recruitment Dynamics: A Case Study of Southern New England/Mid-Atlantic Winter Flounder

Stock size estimates used in stock-recruitment models often assume that reproductive output per individual is equal despite evidence that larger, older spawners contribute diverse spawning behaviors and disproportionately more to reproductive output. This is concerning since depleted population states often coincide with a compromised age structure and increased control of extrinsic forces (environmental conditions or predator-prey dynamics) on stock productivity. In this study, parameterizations of the stock-recruitment relationship for Winter Flounder Pseudopleuronectes americanus, which incorporated covariate metrics describing age structure, temperature, and predation, were compared to identify primary drivers across area-specific data sets that are included in recent regional stock assessments. Four of the six data sets resulted in a top-ranked model that incorporated an age structure metric; however, the age structure metric model was alone in the pool of top-ranked models for only two of these scenarios. In addition, one data set resulted in a base Ricker model, and one resulted in a model that incorporated a predator index. Finally, wavelet analysis identified significant coherence between fishing mortality rate (F) and spawning stock biomass (SSB) for Winter Flounder, which switched from an out-of-phase state to an in-phase state during the 1990s. If the relationship between these model-derived estimates of F and SSB reflects dynamics of the Winter Flounder population, it would have strong implications for management efforts.