Movements and behaviors of swordfish in the Atlantic and Pacific Oceans examined using pop‐up satellite archival tags |
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| Authors: | HEIDI DEWAR ERIC D PRINCE MICHAEL K MUSYL RICHARD W BRILL CHUGEY SEPULVEDA JIANGANG LUO DAVID FOLEY ERIC S ORBESEN DERKE SNODGRASS R MICHAEL LAURS JOHN P HOOLIHAN BARBARA A BLOCK LIANNE M MCNAUGHTON |
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| Institution: | 1. National Marine Fisheries Service, Southwest Fisheries Science Center, 8604 La Jolla Shore Dr., La Jolla, CA 92037, USA;2. National Marine Fisheries Service, Southeast Fisheries Science Center, 75 Virginia Beach Drive, Miami, FL 33149, USA;3. University of Hawaii, Joint Institute Marine and Atmospheric Research, Kewalo Research Facility/NOAA, 1125B Ala Moana Boulevard, Honolulu, HI 96814, USA;4. National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, U.S.A;5. Pfleger Institute of Environmental Research, 315 North Clementine Street, Oceanside, CA 92054 USA;6. University of Miami, RSMAS, 4600 Rickenbacker Causeway, Miami, FL 33149, USA;7. University of Hawaii, Joint Institute Marine and Atmospheric Research, NOAA Fisheries Environmental Research Division, Pacific Grove, CA 93950 USA;8. Fisheries Oceanographer Consultant, LLC, Jacksonville, OR 97530, USA;9. Tuna Research and Conservation Center, Hopkins Marine Station, Stanford University, Oceanview Blvd, Pacific Grove, CA 92950, USA |
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| Abstract: | Swordfish are highly specialized top‐level predators that have been challenging to study. In this paper, data from 31 pop‐up satellite archival tags attached to swordfish from (i) the eastern Pacific, (ii) central Pacific, and (iii) western North Atlantic‐Caribbean were analyzed. Common across locations was a pronounced diel vertical pattern with daytime hours spent primarily below the thermocline and nighttime hours spent in warmer waters, close to the surface. One exception to this pattern was periodic daytime basking events which were most common in cooler waters off California. Maximum daytime depths were significantly correlated with light penetration as measured by the diffuse attenuation coefficient at 490 nm. Temperature did not appear to influence daytime depths, and swordfish tolerated both extremely low temperatures (4°C) and rapid and dramatic temperature changes (>20°C). Temperature did appear to influence the nighttime depths in the Pacific where fish typically remained in the surface mixed layer. In contrast, in the warm tropical Atlantic this was not the case, and nighttime depths were much deeper. In all areas, nighttime depth increased around the full moon. Given the parallels between the vertical movement patterns of swordfish and those of the deep sound scattering layer we suggest that swordfish vertical distribution patterns, especially during daytime, are influenced largely by resource availability. At night, when swordfish are typically targeted by fisheries, both ambient light and temperature influence movements. Understanding vertical movement patterns of swordfish can help evaluate gear vulnerability, improve population assessments, and potentially reduce fisheries bycatch. |
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| Keywords: | Atlantic Ocean deep sound scattering layer diel migration Pacific Ocean satellite tags swordfish |
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