Conservation Letters 4 (2011) 228–233
cetacean carcasses and oil spills 1
Author affiliations:
1Marine Mammal Research Unit, University of British Columbia, Vancouver, Canada
2Department of Biology, Dalhousie University, Halifax, Canada
3Centre for Fish and Fisheries Research, Cetacean Research Unit, Murdoch University, Western Australia
4Cascadia Research Collective, Olympia, WA, USA
5New England Aquarium, Boston, MA, USA
6School of Biology, Aberdeen University, Aberdeen, Scotland, UK
7Nicholas School of the Environment, Duke University, Beaufort, NC, USA
8Humpback Whale Studies Program, Provincetown Center for Coastal Studies, Provincetown, MA, USA
Keywords
Anthropogenic impacts; dolphin; Deepwater
Horizon; Gulf of Mexico; mortality; oil;
strandings.
Correspondence
Rob Williams, Current address: Sea Mammal
Research Unit, Scottish Oceans Institute,
St Andrews Fife KY16 8LB. Tel: +44 (0)1334
462630; Fax: +44 (0)1334 463443.
E-mail: rmcw@st-andrews.ac.uk
Received 23 September 2010
Accepted 15 February 2011
Editor Leah Gerber
doi: 10.1111/j.1755-263X.2011.00168.x
Abstract
Evaluating impacts of human activities on marine ecosystems is difficult when effects occur out of plain sight. Oil spill severity is often measured by the number of marine birds and mammals killed, but only a small fraction of carcasses
are recovered. The Deepwater Horizon/BP oil spill in the Gulf of Mexico was the largest in the U.S. history, but some reports implied modest environmental impacts, in part because of a relatively low number (101) of observed marine mammal mortalities. We estimate historical carcass-detection rates for 14 cetacean species in the northern Gulf of Mexico that have estimates of abundance,
survival rates, and stranding records. This preliminary analysis suggests that carcasses are recovered, on an average, from only 2% (range: 0–6.2%) of cetacean deaths. Thus, the true death toll could be 50 times the number of carcasses recovered, given no additional information. We discuss caveats to this estimate, but present it as a counterpoint to illustrate the magnitude of
misrepresentation implicit in presenting observed carcass counts without similar qualification. We urge methodological development to develop appropriate multipliers. Analytical methods are required to account explicitly for low probability of carcass recovery from cryptic mortality events (e.g., oil spills, ship strikes, bycatch in unmonitored fisheries and acoustic trauma).
Special thanks to Richard Charter