Development of a spatiotemporally integrated per-recruit model for Southern Flounder in the northern Gulf of America

Abstract

Southern Flounder, Paralichthys lethostigma, is an important fish in the northern Gulf of America and has declined throughout its range. In this work, we evaluate a spatially- and temporally-integrated per-recruit model by incorporating information on movement dynamics and spatial differences in fishing pressure. A total of n = 80 Southern Flounder were tagged in Saint Louis Bay, Mississippi with acoustic transmitters. We classified n = 11 individuals as migrators, these individuals exhibiting movement to offshore spawning locations, and n = 16 individuals as residents, these individuals overwintering in inshore habitats. Incorporating the total proportion of migrators, timing of egress from inshore habitats, and differences between inshore and offshore fishing pressure into the spatiotemporally integrated per-recruit model resulted in changes to reference points. In the traditional per-recruit model, at Mississippi’s current minimum size limit of 305 mm, F_0.4 = 0.41 y⁻¹ and F_max = 0.78 y⁻¹; at a size limit of 381 mm, reference points increase to F_0.4 = 0.64 y⁻¹ and F_max = 1.12 y⁻¹. Under the current 305 mm size limit, F_0.4 = 0.41 y⁻¹ and F_max = 0.78 y⁻¹ in the traditional model, while F_0.4 = 0.27 y⁻¹ and F_max = 0.52 y⁻¹ in the integrated model. These contrasts indicate that the stock is more vulnerable when movement is explicitly considered in the model. The results of both traditional and spatiotemporally integrated per-recruit models indicate that changes to the current management regime could benefit the Southern Flounder stock.