Factors affecting catch-and-release mortality of bluefish

Recreational harvests of bluefish Pomatomus saltatrix along the U.S. coast from Maine to Florida exceed commercial harvests, and in recent years about 60-70% of angler-captured fish are released alive. The proportion of fish that survive hooking, handling, and release back to the ocean is unknown; however, if catch-and-release mortality is high, it may represent a significant component of the overall bluefish mortality rate. We estimated long-term (21-d) hooking mortality rates of field-captured bluefish and investigated the effects of various factors on postrelease mortality. Age, length, and the occurrence of bleeding were significant factors associated with catch-and-release mortality, which we estimated to be 38.8%. About 65% of the mortality was initial mortality, and the remainder was delayed mortality. We also performed a laboratory study to examine the physiological response of bluefish to two independent processes (hooking and release versus transfer in coolers to the laboratory) relevant to the field study. Laboratory-held fish that were hooked and released exhibited elevated concentrations of potassium in their blood, suggesting that they experienced either an osmotic imbalance or cellular damage. Laboratory-held fish exposed to the transfer treatment only exhibited osmotic imbalance (elevated plasma sodium concentration) and evidence of anaerobic metabolism (elevated plasma lactate concentration). Our findings indicate that bluefish age and size contribute to variable levels of metabolic stress and that delayed postrelease mortality is considerable.