Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean

Survivorship pop-up archival tags (sPATs) were attached to swordfish (Xiphias gladius) released from U.S. commercial pelagic longline vessels in the western North Atlantic Ocean. The purpose was to determine the postrelease survival of individuals less than the minimum retention size (119 cm in lower jaw fork length) established by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Between 2021 and 2023, 24 sPATs were deployed with a programmed duration of 30 d to measure depth, temperature, and ambient light. Temperature and depth were recorded as daily minimums and maximums, and light level was recorded as a daily change between minimum and maximum values. The final 5 d of depth information were also recorded at 10-min intervals prior to release to assess fine-scale movements consistent with survival. Nineteen tags transmitted data, with 16 tags having data sufficient for analysis. Of these tags, 9 sPATs (56.2%) transmitted data consistent with movements of a surviving swordfish. This survival rate is lower than those reported for previous studies that focused on rod-and-reel and swordfish buoy gear, indicating that capture with pelagic longline gear causes swordfish greater stress than those other gear types. This result, combined with those of prior studies of at-vessel mortality rates, indicates that the current ICCAT rule regarding the minimum retention size provides limited conservation benefits to swordfish stocks.