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Ocean scale hypoxia‐based habitat compression of Atlantic istiophorid billfishes
Author(s) -
PRINCE ERIC D.,
LUO JIANGANG,
PHILLIP GOODYEAR C.,
HOOLIHAN JOHN P.,
SNODGRASS DERKE,
ORBESEN ERIC S.,
SERAFY JOSEPH E.,
ORTIZ MAURICIO,
SCHIRRIPA MICHAEL J.
Publication year - 2010
Publication title -
fisheries oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 80
eISSN - 1365-2419
pISSN - 1054-6006
DOI - 10.1111/j.1365-2419.2010.00556.x
Subject(s) - thermocline , oceanography , overexploitation , pelagic zone , hypoxia (environmental) , upwelling , fishery , tropical atlantic , habitat , environmental science , sea surface temperature , geology , biology , ecology , chemistry , organic chemistry , oxygen
Oxygen minimum zones (OMZs) below near‐surface optimums in the eastern tropical seas are among the largest contiguous areas of naturally occurring hypoxia in the world oceans, and are predicted to expand and shoal with global warming. In the eastern tropical Pacific (ETP), the surface mixed layer is defined by a shallow thermocline above a barrier of cold hypoxic water, where dissolved oxygen levels are ≤3.5 mL L −1 . This thermocline (∼25–50 m) constitutes a lower hypoxic habitat boundary for high oxygen demand tropical pelagic billfish and tunas (i.e., habitat compression). To evaluate similar oceanographic conditions found in the eastern tropical Atlantic (ETA), we compared vertical habitat use of 32 sailfish ( Istiophorus platypterus ) and 47 blue marlin ( Makaira nigricans ) monitored with pop‐up satellite archival tags in the ETA and western North Atlantic (WNA). Both species spent significantly greater proportions of their time in near‐surface waters when inside the ETA than when in the WNA. We contend that the near‐surface density of billfish and tunas increases as a consequence of the ETA OMZ, therefore increasing their vulnerability to overexploitation by surface gears. Because the ETA OMZ encompasses nearly all Atlantic equatorial waters, the potential impacts of overexploitation are a concern. Considering the obvious differences in catchability inside and outside the compression zones, it seems essential to standardize these catch rates separately to minimize inaccuracies in stock assessments for these species. This is especially true in light of global warming, which will likely exacerbate future compression impacts.