Release Mortality of Greater Amberjack from Hook-and-Line Fisheries in the Gulf of Mexico

Gulf of Mexico greater amberjack Seriola dumerili have been designated as currently overfished and undergoing overfishing. Release mortality rates for amberjack in the Gulf of Mexico are unknown, yet releases are projected to increase as regulations become more restrictive. In this study, 1,493 amberjack were tagged and released to estimate release mortality. To date, 11.7% of the released fish have been recaptured, with only 0.3% suffering acute mortality. Recapture of amberjack was proportional to initial capture depth, which indicated that fish did not have increased release mortality with increasing depth of capture. Temperature-depth profiles of hooked amberjack obtained using Sensus Ultra data loggers showed varying but rapid ascent rates from 0.2 m/sec to as high as 1.2 m/sec. Lack of a typical depth/release mortality relationship may be due to amberjack self-venting or “blowing bubbles” when ascending, with the spontaneous release of gas from their swim bladders increasing with capture depths >50 ft. Size of fish and blood L-lactate concentration were related to fight time duration although muscle lactate levels were not. Release mortality for greater amberjack appeared to be affected by factors other than capture depth and was less than the assumed release mortality used in the current stock assessment.