Red Snapper, Lutjanus campechanus, Mortality, Movements, and Habitat Use Based on Advanced Telemetry Methods
Williams-Grove, Laura Jay
Type of DegreeDissertation
DepartmentFisheries and Allied Aquacultures
MetadataShow full item record
Ultrasonic telemetry was used to estimate the success of a new release method, mortality, movements (m to km), and depth patterns for red snapper, Lutjanus campechanus, (n = 86) around artificial reefs in the northern Gulf of Mexico. Mortalities, fine-scale movements (~1 m accuracy) and emigrations were estimated over 3 years from > 5 million fish positions, based on a VEMCO Positioning System (VPS, Vemco Ltd, Nova Scotia) deployed at four different reef sites. In addition a surrounding array (64 m2) of 22 receivers, located on other reef sites at 1.6 km distances was used to validate emigrations and larger movement patterns (km). A remotely opening cage was used to release transmitter tagged fish and successfully (100%) protected fish from predation following release. The VPS system validated the fate of 98% of the released fish around the artificial reefs (independent of fishery). A high fishing mortality and low natural mortality were observed during short federal recreational fishing seasons (42 to 9 days). For all years combined total instantaneous mortality (Z) was 0.45 (0.28 – 0.67). Red snapper movements showed high residency (34 months) and site fidelity (85% y -1) to artificial reefs. Depth patterns, two-dimensional (2D) and three-dimensional (3D) home range (95% kernel density estimates; KDE) and core areas (50% KDE) significantly changed over seasonal, monthly, and diel time periods. In the winter months, deeper depths (mean ± SD, 26 m ± 3 m) and fewer movements (area and volume) were observed, with fish mostly (99% of time) staying near their VPS site. During fall and summer months, shallower depths (18 m ± 5 m) and larger movements were observed with up to 31% of time spent on secondary sites within the VPS array. Over diel periods, most red snapper (3 out of 4 VPS sites) showed larger movements during the day, smaller areas during the night, and least movement during dusk and dawn. The surrounding receiver array showed that red snapper typically moved short distances (~ 1.5 km), remained on these secondary sites for prolonged periods (23 – 336 d), were then caught, emigrated out of the array, or returned to their release sites. The long-term use of the VPS reefs (> 1,095 d) showed high residency, site fidelity and mortality for larger red snapper. Red snapper movement patterns were most likely related to foraging, spawning and predator evasion (i.e., quick movements over open habitat, short emigration distances, paired emigrations, and reduced movements at dawn and dusk).
- Final Williams-Grove Dissertation Dec 2015.pdf