Quantifying overlap between the Deepwater Horizon oil spill and predicted bluefin tuna spawning habitat in the Gulf of Mexico.

Elliott L Hazen,Michael R Castleton,Steven G Wilson,Robert J Schallert,Michael J W Stokesbury,Barbara A Block,Aaron B Carlisle,James E Ganong,Steven J Bograd

doi:10.1038/srep33824

Abstract

Atlantic bluefin tuna (Thunnus thynnus) are distributed throughout the North Atlantic and are both economically valuable and heavily exploited. The fishery is currently managed as two spawning populations, with the GOM population being severely depleted for over 20 years. In April-August of 2010, the Deepwater Horizon oil spill released approximately 4 million barrels of oil into the GOM, with severe ecosystem and economic impacts. Acute oil exposure results in mortality of bluefin eggs and larvae, while chronic effects on spawning adults are less well understood. Here we used 16 years of electronic tagging data for 66 bluefin tuna to identify spawning events, to quantify habitat preferences, and to predict habitat use and oil exposure within Gulf of Mexico spawning grounds. More than 54,000 km2 (5%) of predicted spawning habitat within the US EEZ was oiled during the week of peak oil dispersal, with potentially lethal effects on eggs and larvae. Although the oil spill overlapped with a relatively small portion of predicted spawning habitat, the cumulative impact from oil, ocean warming and bycatch mortality on GOM spawning grounds may result in significant effects for a population that shows little evidence of rebuilding.

Highlights

The Atlantic bluefin tuna (Thunnus thynnus) is a large endothermic, highly migratory species that is broadly distributed throughout the Atlantic Ocean from the waters off Greenland and Norway in the north to Argentina in the south[1,2,3]
Tag data from 1997–2014 indicate that the peak occupancy in the Gulf of Mexico (GOM) for bluefin tuna (40% of tagged fish) occurs from March 15th to May 31st (Fig. 1A,B) which agrees with previous analyses of Atlantic bluefin tuna electronic tag data, larval data, and bycatch data[7,11,12,46]
The summary statistics showed that these variables remained significant across all 60 runs of the models (100%), except for SSHa and SSHsd, which were significant in 78% and 93% of the correlated random walks (CRWs) iterations respectively (Table 1)

Summary

Introduction

The Atlantic bluefin tuna (Thunnus thynnus) is a large endothermic, highly migratory species that is broadly distributed throughout the Atlantic Ocean from the waters off Greenland and Norway in the north to Argentina in the south[1,2,3]. Following feeding in the waters off the east coast of North America, fish from the western Atlantic stock migrate south to the GOM from November to August with a peak in spawning during the spring and early summer[6,12,15,16]. Both the GOM and Mediterranean Atlantic bluefin tuna populations have been greatly reduced due to overexploitation, the GOM population is smaller and has been more heavily impacted by overfishing than the Mediterranean population[17]. Continued monitoring of adult tuna in addition to the 2010 year class is needed to understand population level effects

Methods

Results

Conclusion