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

• Main Author: Young, Zachery
• Format: Text
• Language: unknown
• Published: NSUWorks 2023
• Subjects: Post-release Mortality; U.S Fisheries; Highly Migratory Species (HMS); Vertical Habitat Utilization; billfish; Southeast United States; sPAT tag; Aquaculture and Fisheries; Marine Biology; North Atlantic; Northwest Atlantic
• Online Access: https://nsuworks.nova.edu/hcas_etd_all/172; https://nsuworks.nova.edu/context/hcas_etd_all/article/1186/viewcontent/auto_convert.pdf

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.