In the Gulf of Mexico, bottlenose dolphins are split into two distinct groups: coastal and offshore. Coastal bottlenose dolphins are smaller in size than the offshore group, and the two groups likely do not interbreed. Bottlenose dolphins are a common saltmarsh resident in Louisiana, where they travel up saltmarsh bayous and canals to fish. Resident groups have strong site fidelity and will not leave the area where they’re born, meaning that coastal Louisiana bottlenose dolphin populations are reliant on healthy saltmarshes for survival.
At least 900 bottlenose dolphins died as a direct result of the Deepwater Horizon oil spill in 2010, but the disaster’s overall effect on the coastal population isn’t well known. There was little bottlenose dolphin monitoring prior to the spill in Louisiana, which makes it difficult to make any before and after comparisons of the population. However, bottlenose dolphins in coastal areas directly affected by oiling have been found to have serious health problems such as liver and respiratory diseases. Studies with these findings indicate that the oil exposure may therefore have had damaging long-term effects on the Louisiana population. Settlement money from the spill is being used to finding new ways to monitor bottlenose dolphins in the Gulf of Mexico. One promising approach is the use of underwater acoustic recording to identify the Gulf’s 13 dolphin species by their echolocation clicks, which differ between species. Such data can be used to estimate species diversity and to track population abundances through time.
References: Gulf Spill Restoration. Study by NOAA and Partners Shows Some Gulf Dolphins Severely Ill. (http://www.gulfspillrestoration.noaa.gov/2012/03/study-shows-some-gulf-dolphins-severely-ill)
Frasier, K. E., M.A. Roch, M.S. Soldevilla, S.M. Wiggins, L.P Garrison, and J.A. Hildebrand. 2017. Automated classification of dolphin echolocation click types from the Gulf of Mexico. PLoS Comput Biol 13(12): e1005823. https://doi.org/10.1371/journal.pcbi.1005823