Fish Size and Exposure to Air: Potential Effects on Behavioral Impairment and Mortality Rates in Discarded Sablefish

Abstract

Fisheries models often assume that discarded undersized fish and target species will survive and contribute to future recruitment and yield. If smaller fish are more susceptible to capture stressors than larger fish, then the assumption that smaller discards would contribute to recruitment may not be true. We tested the hypothesis that small sablefish Anoplopoma fimbria show more behavioral impairment and mortality than large fish when exposed to air (10–60 min) at various temperatures (10–18°C). Sablefish captured by trawl, longline, or trap are commonly exposed to these conditions during warmer seasons when brought up on deck and sorted. Two size-classes of fish (small: 32–49 cm total length (TL); large: 50–67 cm TL) were used in the experiments. Behavior was measured as upright orientation and startle responses to visual and mechanical stimuli 1, 2, 3, and 24 h after air exposure; mortality was measured through 7 d after air exposure. Small fish mortality increased as air time increased and was at higher levels than in large fish. Only 10 min of air exposure caused behavioral impairment in small and large fish, which could lead to increased predation on discarded fish. At 24 h after air exposure, normal behavior had not generally resumed and small fish had more behavioral impairment than large fish.