Seasonal movements of Gulf of Mexico sperm whales following the Deepwater Horizon oil spill and the limitations of impact assessments

• Published in: Marine pollution bulletin 2020-12, Vol.161 (Pt A), p.111627, Article 111627
• Main Authors: Morano, Janelle L., Tielens, Jamey T., Muirhead, Charles A., Estabrook, Bobbi J., Sullivan, Patrick J., Dugan, Peter J., Clark, Christopher W., Rice, Aaron N.
• Format: Article
• Language: English
• Subjects: Acoustic surveying; Animals; Aquatic mammals; Baseline studies; Bioacoustics; Cetacea; Cetacean; Continental shelves; Damage assessment; Deep water; Echo surveys; Environmental Monitoring; Gulf of Mexico; Impact assessment; Marine mammals; Monitoring; Natural resources; Oil; Oil spill; Oil spills; Passive acoustic monitoring; Petroleum Pollution; Population ecology; Presence; Seasons; Shelf edge; Sperm Whale; Water Pollutants, Chemical - analysis; Whales; Whales & whaling
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2020.111627

As part of the Deepwater Horizon Oil Spill Natural Resource Damage Assessment in the Gulf of Mexico, we conducted a large passive acoustic survey across the eastern Gulf continental shelf edge to assess impacts to sperm whale population. In the months immediately after the spill, sperm whale occurrence was significantly higher in areas closest to the spill. Over the following seasons in 2010–2011, we documented cyclical patterns of decreased and increased occurrence suggesting that this population exhibits a seasonal occurrence pattern in the region, with seasonal movements to other regions, and not likely directly influenced by the oil spill. Unfortunately, a lack of adequately scaled, pre-spill data on sperm whales, along with limitations on the survey duration constrain our ability to infer spill-related changes in sperm whale occurrence. However, our study establishes post-disaster baseline data for continued monitoring, and an expanded study design could provide a model for continued monitoring. •Large-scale passive acoustic survey of sperm whales following the BP Deepwater Horizon oil spill.•Seasonal occurrence, with highest in summer, lowest in winter.•Sperm whale occurrence along continental shelf highest near oil spill origin•Results suggest other factors influence occurrence more than oil spill.•Lack of baseline data and limitations and timeline of federal legal assessment process constrain sufficient impact assessment.