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NOAA Scientists Study Effects of Oil Spill on Bluefin Tuna

Swordfish PictureA 5 mm long larval stage of bluefin tuna collected during the cruise this April aboard NOAA Ship Gordon Gunter.

NOAA Fisheries scientists continue to study the possible effects of last year’s Deepwater Horizon/BP oil spill on Atlantic bluefin tuna, a valuable fish species prized by commercial and recreational fisheries. 

Since the April 2010 disaster, NOAA has been carefully monitoring bluefin tuna in the Gulf of Mexico by collecting larval samples during the spring spawning season, analyzing reports from scientific observers aboard fishing vessels and tracking the movement of tagged bluefin tuna.   SEAMAP surveys have been conducted since 1982, providing a long time-series of information on bluefin tuna larvae that helps scientists analyze trends in the data.

The Gulf of Mexico is one of the only known spawning grounds for the western stock of Atlantic bluefin tuna. In fact, April and May are the peak spawning months for the tuna, and scientists have been concerned about possible impacts of oil and dispersants used to clean up spilled oil on this important fish species. 

Swordfish PictureA 7 mm long bluefin tuna larvae collected this April aboard the NOAA Ship Gordon Gunter. Taxonomy and genetics were combined to confirm the identity of this larval fish.

Tagging studies tell a story

In May 2010, NOAA scientists deployed satellite tags on four bluefin tuna caught in the vicinity of the oil spill. All fish completed their migration up to the Grand Banks and Gulf of St. Lawrence, where the tags separated from the fish on schedule after 90 days, floated to the surface, and reported data on the bluefin’s movements via satellites passing overhead
(view migration map). 

Researchers plan to deploy an additional 46 tags this year as part of an expanded study to assess the range of depths inhabited by bluefin tuna and

the length of time they spend in the Gulf of Mexico each year. The bluefin

Swordfish PictureLeft to right: (left to right) Lourdes Vasquez-Yeomans, a scientist from Mexico's El Colegio de la Frontera Sur and Estrella Malca, scientist with NOAA's Southeast Fisheries Science Center.

tagging studies will contribute to scientists’ understanding of this species’ potential exposure to hazardous chemical compounds following the BP spill. 

One tuna, two tuna, three tuna, four …

The annual SEAMAP research cruise is currently sampling bluefin tuna larvae to evaluate its abundance in the Gulf, another important source of information about the potential impact of the oil spill on bluefin spawning in the Gulf.

Although some bluefin tuna larval habitat was found in the vicinity of the oil spill, it appears the majority of historic bluefin tuna larvae habitat is located outside the spill area.  NOAA scientists are aboard the NOAA Ship Gordon Gunter on the first two of four legs of the 2011 larval bluefin tuna survey. During this cruise, they are collecting plankton samples along with data on water temperature, salinity, and chlorophyll levels.  The plankton samples are sorted for larvae, including larvae of tunas, mackerels and bonito. The larvae will then receive further analysis.  

 

Spreading the data around

Swordfish PictureLourdes Vasquez-Yeomans, a scientist from Mexico's El Colegio de la Frontera Sur examines freshly collected samples of larvae inside the laboratory of the NOAA Ship Gordon Gunter while at sea.

Both the western and the eastern (Mediterranean) stocks of bluefin tuna are managed internationally by the International Commission for the Conservation of Atlantic Tunas (ICCAT) under rebuilding plans.  ICCAT’s conservation and management measures are implemented in the United States through strict regulation of commercial and recreational fisheries that catch bluefin tuna, including a prohibition of targeted fishing for bluefin tuna in the Gulf of Mexico. 

The work by NOAA researchers will be shared with other international experts participating in ICCAT’s scientific committee and will be considered during efforts to evaluate stock status.  NOAA and the Food and Drug Administration are also continuing laboratory tests to ensure that bluefin tuna and other seafood products are safe for consumers.