Consumption and gastric evacuation in juvenile red drum Sciaenops ocellatus (Linnaeus): Estimation of prey type effects and validation of field-based daily ration estimates

Abstract

The red drum Sciaenops ocellatus (Linnaeus) is a dominant member of southeastern U.S.A. estuarine systems that feeds on numerous species of commercial and recreational value. Recovering red drum stocks highlight the need for quantification of feeding habits and rates of consumption to assess predatory impact. To validate field-based estimates of gastric evacuation rates and daily ration, a series of controlled laboratory experiments was completed for juvenile and sub-adult red drum (~60–600g). Influential factors examined included water temperature (17°C and 27°C), prey type (fish and crustacean prey), and red drum body size (small x¯=76.3g; large x¯=429.2g). Average maximum consumption rate varied between red drum body sizes and water temperatures. Small drum fed at a mean (±SD) rate of 18.9±0.6% body massd−1 at 27°C and 9.6±0.6% body massd−1 at 17°C, while large drum fed at a rate of 12.5±0.8% body massd−1 at 27°C and 6.3±0.4% body massd−1 at 17°C. Gross growth efficiency was generally consistent across factors, ranging between 13.2 and 16.3%, with small red drum being slightly more efficient. The rate of gastric emptying was influenced most by temperature and ranged from 4.0 to 9.4%h−1. The red drum body sizes and prey types we tested demonstrated only modest effects, with slightly faster evacuation rates by smaller red drum and for anchovy prey. Among the eight factor combinations (red drum size×water temperature×prey type) tested during gastric evacuation trials, half (four) of the relationships were best described by the square root model. However, model selection approaches revealed that multiple models provided adequate fit in nearly all cases. Laboratory estimates of red drum gastric evacuation and maximum consumption confirmed that previous field-based estimates were plausible.