The Use of Ultrasonic Telemetry to Estimate Residency, Movement Patterns, and Mortality of Red Snapper, Lutjanus campechanus

Abstract

Site fidelity, emigration, and mortality were estimated from telemetry for large (500 – 860 mm TL) red snapper Lutjanus campechanus (N = 87) from four artificial and one natural reef in the northeastern Gulf of Mexico. From December 2005 to December 2008 we used arrays of five ultrasonic receivers at each site. Each array consisted of one receiver at the center with four receivers placed 420 or 1100 m north, south, east, and west of center. As of October 2008, 21% were caught, 34% emigrated, 12% died, 29% are still present, and 4% uncertain. Estimates of total mortality (Z) ranged from 0.54 to 0.58, fishing mortality (F) from 0.38 to 0.45, and natural mortality (M) from 0.11 to 0.17 using various methods. Median residence time was 572 d, and residence time ranged from 1 to 829 d, with 68% of fish staying at least one year at the site and 80% were present for at least 200 d. Some fish did not show constant residency to one site. Some fish showed directed movements to other sites (~8 km away), and some returned after emigrating. A local regression procedure showed detections at the center receiver were significantly greater during the day than at night, while detections on outside receivers were greater around sunset. Red snapper (N = 6) manually tracked for continuous 24-h periods stayed near (< 60 m) the artificial reef (75% of locations within 20 m of the structure), and were significantly further away at night (mean = 19.0 m) than day (mean = 12.2). These patterns suggested that fish tend to move away from the reef at night. Home range size and mean distance from the reef were significantly affected by fish size (range = 550 to 710 mm); larger fish had a greater mean distance and home range size. Estimated mortality rates were similar to past estimates while residence time was longer than any previous estimate. The short-term patterns of fish staying close to structure, and the long-term residency of these fish to the sites indicated that these artificial reef structures provided suitable habitat for red snapper.