Mortality Estimates for Red Snapper Based on Ultrasonic Telemetry in the Northern Gulf of Mexico

We used the Vemco Positioning System (VPS) to estimate mortalities from the fine-scale movements (similar to 1-m accuracy) of Red Snapper Lutjanus campechanus on four artificial reef sites in the northern Gulf of Mexico in 2012, 2013, and 2014. Additional receivers on surrounding reef sites validated emigrations of tagged Red Snapper from the VPS-monitored sites. We tagged and released 86 Red Snapper and tracked 59 fish for extended periods (17 to 1,096 d). Telemetry tracking patterns identified fish status as active, emigrated, caught (F), or dead (M) at monthly intervals. At the end of the study, 17 fish had emigrated, 24 were caught by fishers, and 18 were active on VPS-monitored reef sites. For all years combined, annual fishing mortality was F = 0.44 (0.27-0.65, 95% confidence limit). In 2012, F = 0.72 (0.35-1.31) and was higher than other years, but the number of fish available for recapture at the start of the sportfishing season was low (n = 15). In 2013, F = 0.18 (0.07-0.42; n = 30), and in 2014, F = 0.42 (0.22-0.76; n = 28). One natural mortality (M) was detected in 2012, and M = 0.12 (0.02-0.69); no subsequent natural mortalities were detected in 2013 and 2014 (M = 0). Total instantaneous mortality (Z) for all years was Z = 0.48 (0.30-0.70). We attributed the low M to high fishing mortality but caution that sample sizes were small, which is typical of telemetry studies. The fates of 58 (98%) transmitter-tagged Red Snapper were successfully identified based on the VPS technology. Increases in F from 0.18 (2013) to 0.42 (2014) occurred when the length of the fishing seasonwas decreased (42 to 9 d) and indicated that fishers increased effort during the shortened fishing season, and the management goal of reducing catch may not have been achieved.