Estuarine effects on the growth and life-history strategy of largemouth bass

Relative to inland populations, largemouth bass (Micropterus salmoides) in Alabama’s Mobile-Tensaw River Delta (MTRD) have slow growth, high condition, and low annual survival similar to other coastal populations.  To evaluate the estuarine effects on growth of largemouth bass we incorporated the metabolic cost of salinity into a bioenergetics model.  Bioenergetics simulations suggested that salinity, high peak summer temperatures, and consumption of lower caloric density invertebrates (e.g., blue crabs) reduced growth in both downstream and upstream regions of the MTRD and were correlated with discharge.  Metabolic costs of salinity increased with mass, and mean caloric density of consumed prey declined with age due to the greater incorporation of blue crabs into the diet, reducing the growth potential of larger fish, particularly in the downstream region.  Embedding bioenergetics constraints into a life-history model revealed that the estuarine environment may increase the likelihood of maturing at younger ages in the downstream versus the upstream region, consistent with field observations of both age- and size-at-maturation.  These results suggest that there may be selective pressure against coastal largemouth bass growing to large sizes due to the high negative energetic consequences resulting in a live-fast, die-young life-history strategy.