| EXPERIMENTAL EVALUATION OF PATTERNS AND MECHANISMS OF JUVENILE RED DRUM MORTALITY DUE TO ACUTE COLD STRESS DURING SEVERE WINTERS |
| ANDERSON, DEENA A. and Scharf, Frederick S., University of North Carolina Wilmington, Wilmington, NC, USA, 28403, daa2211@uncw.edu, scharff@uncw.edu |
| Early life history processes can determine recruitment patterns of fishes. Red drum, a dominant sport fish throughout the US South Atlantic and Gulf of Mexico, spend their first 2-3 years in estuarine waters and are believed to overwinter in these habitats. Age-0 red drum in North Carolina experience the most extreme cold temperatures in the species range. We conducted a series of controlled laboratory experiments over two winters to identify survival patterns and physiological responses related to acute cold in age-0 red drum. Temperature data from North Carolina estuaries were used to identify overwinter minima and characterize cold fronts. During the first winter, water temperature treatments of 1, 3, and 5C represented extreme cold, with a 10C control treatment. Year 2 experiments were designed to simulate the passage of cold fronts. High and low frequencies (i.e., temporal spacing) of fronts were fully crossed with durations of 24 or 48 hours spent at the temperature minimum of 3C. Experimental designs in both years included three replicate tanks at each treatment and tested for a body size effect (4 temperature treatments x 2 body sizes x 3 replicates = 24 replicate tanks each winter). Fish behavior and mortality was recorded regularly, and blood and tissue samples were collected from cold-stressed and control fish for physiological analyses. First winter results indicate that juvenile red drum survival improves at 5C as opposed to 1 or 3C. However, survival at 3C was higher when exposure was reduced in duration, as observed during a simulated cold front. Through a better understanding of winter mortality related to acute cold stress, managers may refine predictions of year-class strength and adjust fishery regulations accordingly. |
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