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Marine Ecology Progress Series

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MEPS 452:219-236 (2012)  -  DOI:

Modeling swordfish daytime vertical habitat in the North Pacific Ocean from pop-up archival tags

Melanie Abecassis1,*, Heidi Dewar2, Donald Hawn1,4, Jeffrey Polovina3

1Joint Institute for Marine and Atmospheric Research, University of Hawaii, 1000 Pope Rd., Honolulu, Hawaii 96822, USA
2Southwest Fisheries Science Center, NOAA Fisheries, 8604 La Jolla Shores Dr., La Jolla, California 92037, USA
3Pacific Islands Fisheries Science Center, NOAA Fisheries, 2570 Dole St., Honolulu, Hawaii 96822, USA
4Present address: Pacific Islands Regional Office, NOAA Fisheries, 1601 Kapiolani Boulevard, Suite 1110, Honolulu, Hawaii
96814, USA

ABSTRACT: The daytime foraging depth of swordfish in the North Pacific was investigated with data from an 8 yr tagging program, using 28 Wildlife Computer pop-up archival tags deployed on swordfish in the North Pacific. The tags transmitted data from 1°S to 44°N latitude and from 206 to 249°E longitude. Five tags were recovered, providing a full archival record that showed that when swordfish did not engage in daytime basking behavior, they remained within a narrow range of light level during both day and night, suggesting swordfish stay within a sound-scattering layer (SSL) to feed during both day and night. Daytime mean depth of non-basking swordfish ranged from 32 to 760 m. Seventy-seven percent of the daytime mean depth could be explained with a generalized additive model that used 3 environmental indices: satellite-derived surface chlorophyll as a proxy for light at depth, oxygen at 400 m obtained from the World Ocean Atlas, and temperature at 400 m inferred from the tag data. This model, when used in a predictive mode, generated a basin-wide map of swordfish daytime mean depth that showed depths exceeding 600 m to the north of Hawaii, shoaling to 300 m off the coast of California. This information could improve daytime swordfish catch by longliners and potentially allow them to switch from shallow night sets that result in interactions with sea turtles. This approach in effect defines the habitat of swordfish prey, giving us insight into the vertical behavior of those mid-trophic level organisms inhabiting the SSL. Our model could be easily applied to other deep-foraging species.

KEY WORDS: Xiphias gladius · Swordfish · Satellite tracking · Generalized additive model · Habitat modelling

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Cite this article as: Abecassis M, Dewar H, Hawn D, Polovina J (2012) Modeling swordfish daytime vertical habitat in the North Pacific Ocean from pop-up archival tags. Mar Ecol Prog Ser 452:219-236.

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