Physiological, temporal, and environmental determinants of dry energy densities of low trophic-level fishes in the Gulf of Mexico

Abstract

Low trophic-level fishes provide a link to higher trophic-level animals, including birds, mammals, and economically valuable fishes. Despite their role, the dry energy density (DED) of these fishes and its variability have not been described in the northern Gulf of Mexico (nGOM). To address this, we describe species-specific DED for four fish species in the nGOM: Atlantic Croaker (Micropogonias undulatus), Gulf Menhaden (Brevoortia patronus), White Trout (Cynoscion arenarius), and Bay Anchovy (Anchoa mitchilli). We investigated the impacts of body length, life stage (juvenile and adult), month of collection, and river discharge from the Mississippi River to determine the response of DED for Atlantic Croaker and Gulf Menhaden. Using bomb calorimetry, we found that the DED of Atlantic Croaker ranged from 3021 to 6445 calories/g (mean = 4524 ± 646 calories/g SD, n = 129), Gulf Menhaden DED ranged from 2578 to 6821 calories/g (mean = 5069 calories/g ± 794 SD, n = 193), White Trout DED ranged from 3118 to 4581 calories/g (mean = 4120 calories/g ± 358 SD, n = 30), and Bay Anchovy DED ranged from 3925 to 4387 calories/g (mean = 4261 ± 126 calories/g SD, n = 74). The mean DED of Gulf Menhaden and Atlantic Croaker varied and was at a minimum during the fall. The DED of Gulf Menhaden and Atlantic Croaker were linearly, positively, and significantly (α = 0.05) related to fork length (R2 = 0.23 and R2 = 0.32, respectively). The flow rate of the Mississippi River was not a significant predictor of the DED of juvenile or adult Gulf Menhaden but was a significant predictor of the DED of adult Atlantic Croaker (p < 0.001, R2 = 0.04). The species-specific energy density values and the variations due to the month of collection, environmental conditions, and physiological variation will serve to inform ecosystem models.