Defense Date
12-8-2023
Document Type
Thesis
Degree Type
Master of Science
Degree Name
Marine Science
First Advisor
David Kerstetter, Ph.D.
Second Advisor
Joshua Feingold, Ph.D.
Third Advisor
Walter Golet Ph.D.
Keywords
Post-release Mortality, U.S Fisheries, Highly Migratory Species (HMS), Vertical Habitat Utilization, billfish, Southeast United States, sPAT tag
Abstract
This study used survivorship pop-up archival tags (sPAT) tags to determine the post-release survival and habitat use from twenty-four undersized swordfish captured in the northwest Atlantic Ocean during normal operation within the commercial U.S pelagic longline industry. From these deployments, sixteen tags were used to determine post-release survival, and eight of the surviving tags were used to analyze short-term habitat utilization. Mortality was estimated to be 43.8% and was not significantly affected by variables such as fish size, latitude caught, or horizontal distance traveled. The relatively high mortality, in combination with the high at-haulback mortality reported in previous studies, does not suggest that the current minimum retention limit set by policy makers is effective at maintaining a sustainable fishery. Most swordfish exhibited a northward movement consistent with known migratory patterns of this species, however some showed localized habitat preference and appeared to stay in a localized area near the tagging location. The average speed of swordfish was 12.24 km/day. Swordfish exhibited a typical diel vertical migration pattern, inhabiting waters shallower than 100 m during the night and going to an average depth of 544 m during the day. This movement exposed swordfish to a wide range of temperature variation, ranging between 5°C and 28.9°C. Size was not a significant factor in depth or temperature preference.
NSUWorks Citation
Zachery Young. 2023. Evaluating Post-release Survival and Habitat Utilization of Undersized Swordfish (Xiphias gladius) Caught by the U.S Pelagic Longline Fishery in the Western North Atlantic. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (172)
https://nsuworks.nova.edu/hcas_etd_all/172.