 Gulf Spawning Ground Designated as Critical Habitat
The National Marine Fisheries Service (NMFS) has designated a Habitat Area of Particular Concern (HAPC) for spawning bluefin tuna in the Gulf of Mexico. The area (shown in green at right) is based in large part on spawning habitat identified through our electronic tagging research. The Gulf of Mexico is the only known spawning ground of the severely depleted western Atlantic bluefin tuna, and TAG applauds NMFS for recognizing its importance to the future of this unique population.
Because an HAPC’s regulatory power focuses on habitat, this designation does not impact the pelagic longline fisheries that target yellowfin tuna and swordfish in the region – and also incidentally catch bluefin tuna. However, HAPC designation could limit other future operations determined to disturb bluefin spawning habitat.
The Bluefin Tuna Buddy System
 Our Fall 2008 tagging in Canada is paying amazing dividends as tag after tag is popping up and reporting incredible data. Two tags deployed on the same day last fall (10/25/08) popped up within 6 miles of each other on May 29th, off the east coast of Florida. This alone would make these tags interesting -- but the plot thickens: the May 29th pop-ups were premature releases for both fish, which were not scheduled to pop off until late June, and we hypothesize that deep dives (>3,000 ft!) as the tuna exited the Gulf of Mexico (GOM) caused the tags to release.
The tag tracks indicate that these two giants (measuring 105 inches and 115 inches upon tag-and-release) mingled on the GOM spawning grounds for several weeks during late April through early May. The fascinating part of these fish's presumed spawning activity is that it occurred in the northcentral and northeastern GOM, rather than the northwestern Gulf where most of our tagged fish have bred.
Given that these fish were tagged on the same day, in the same place - and spawned at the same time, in the same place - and their tags popped up in the same place, on the same day, one might assume that these two fish were part of a school that stuck together. Not so! Despite the similarities, these two fish took two very different migratory routes to the same GOM spawning area. One fish took a more inshore route, spending 2-3 weeks in late November/early December feeding in North Carolina, while the other fish remained offshore. This shows an intriguing fidelity to spawning and feeding areas despite different migratory routes.
Data Highlight: For a couple weeks in the Gulf of Mexico, tagged bluefin tuna exhibit a unique diving behavior thought to represent courtship and spawning. The oscillatory, nighttime diving pattern - seen nowhere else in TAG's tagging - is thought to indicate spawning at the surface, interspersed with repeated shallow dives into cooler waters to literally chill out. One week of this behavior is shown in the figure above. Dark bars indicate nighttime. Depth (black), water temperature (blue) and body temperature (red) are included. |
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Tags Out
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Data In
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Atlantic
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1025
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506
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Pacific
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612
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355
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