Population effects of shrimp trawl bycatch on Atlantic croaker

We used stage-within-age based matrix models of Atlantic croaker (Micropogonias undulatus) in the Gulf of Mexico and the South and Mid-Atlantic bights to explore the population-level impacts of shrimp trawl bycatch on estuarine-dependent fishes and to investigate tradeoffs between directed adult fisheries and bycatch mortality. The Gulf model reflected a rapidly declining population, while the Atlantic population showed a modest decline. Elasticity analyses indicated that both populations were more sensitive to the summed survival of adults than first-year survival, particularly in the Gulf. Contrary to our expectations, bycatch mortality on late juveniles was not the most important factor affecting either population of Atlantic croaker, and this result was robust to uncertainty in both adult and late juvenile mortality estimates. Both populations were most sensitive to ocean larva mortality, followed by mortality of estuary larvae and adults in the Gulf and of early juveniles and adults in the Atlantic. Nonetheless, bycatch mortality did have a large negative impact on population growth rates, and reducing late juvenile or adult mortality by about 35% in the Gulf or 5% in the Atlantic should reverse population declines. Bycatch reduction devices currently in use can achieve these desired reductions.