Post-Release Survival and Habitat Utilization of Juvenile Swordfish in the Florida Straits

The use of pop-up satellite archival tags (PSATs) eliminates many of the limitations associated with acoustic and conventional tags by using fishery-independent data collection and retrieval. Previous research techniques have provided information on longer-term movements, migrations, and behavior patterns, but there is still a need for additional tagging studies using tags with depth and light data and increased memory that will further define the short-duration activity patterns and habitat utilization of juvenile swordfish in the western North Atlantic. PSATs have been successfully used on other large pelagic fishes, but have yet to be used on juvenile swordfish. This study investigated two main topics: a) the post-release survival rates of juvenile swordfish after being released from the recreational rod-and-reel fishery and commercial swordfish buoy gear fishery in the Florida Straits, and b) the habitat utilization of juvenile swordfish following release. High-resolution PSAT technology was used to estimate the post-release survival of 16 individual juvenile swordfish captured with standard recreational or buoy fishing gear and techniques in the southeast Florida swordfish fishery. Analysis of release mortality estimates was done using the “Release Mortality” Program. Five of the fourteen reporting tags showed a mortality within 48 hours, for a release mortality rate of 35.7%. However, no common thread could be found among the five mortalities. Results of the Release Mortality program indicated that if the true mortality rate was 35.7%, approximately 1800 tags would have to be deployed to increase the precision of the mortality estimates to +/- 5% of the true value. The nine surviving fish varied in straight-line distance traveled and in direction, and could withstand a wide range of temperatures. A deterministic, periodic model was developed to fit to the data and describe the fishes’ habitat utilization. This model identified both diurnal and lunar signals in the data, confirming that juveniles do move vertically based on the daily cycle of the sun and the lunar cycle of the moon and that their diurnal movements are much greater than their lunar movements. The results of this study can be valuable to management practices in future stock assessments and decisions regarding mandatory release of undersized fish