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How Many in the Sea? Automatic Detection of Ribbon Seals

Ribbon Seal on IceIn 2008, J. Clifford wrote about the delisting of the ribbon seal under the Endangered Species Act, noting that the Bush administration was late in its determination but admiring the unusual deference to scientific opinion by the conservative president.  At the time, the ribbon seal numbers were listed at approximately 200,000.  In 2009, the Center for Biological Diversity sued to put the ribbon seal back under government protection, but agreed under negotiation to a process in which the National Oceanic and Atmospheric Administration would make a reevaluation and finding by November 2010.  It took NOAA a few more years than that, but in July 2013, under the aegis of the Obama administration, NOAA issued a report drawing on available evidence to reaffirm the delisting of ribbon seals from protection.  According to NOAA, hunting of these seals has declined and threats to populations from declining ice extent are largely a concern for future years, not the present.

A fascinating aspect of this policy decision is the deceptively simple question, how many ribbon seals are there in the sea?  The world’s oceans are huge, dark and impossible to constantly scan; an actual census of seals is practically impossible at the current time.  So how did NOAA estimate that ribbon seal populations were at a reasonable level?  The agency relied primarily on the work of Jay Ver Hoef and associates, who flew 300 meters over the Eastern Bering Sea over one week’s time, taking automated photographs of the area and consulting photographs when they matched with infrared heat signatures.  The resulting sample was analyzed using spatial hierarchical modeling to arrive at a rough estimate.

Conn, P. B., Ver Hoef, J. M., McClintock, B. T., Moreland, E. E., London, J. M., Cameron, M. F., … & Boveng, P. L. (2014). Estimating multispecies abundance using automated detection systems: ice‐associated seals in the Bering Sea. Methods in Ecology and Evolution, 5(12), 1280-1293.

Ver Hoef, J. M., Cameron, M. F., Boveng, P. L., London, J. M., & Moreland, E. E. (2014). A spatial hierarchical model for abundance of three ice-associated seal species in the eastern Bering Sea. Statistical Methodology, 17, 46-66.

Both of these papers are available for reading without any fees if you search for them via Google Scholar.  I suggest at least a quick scan.

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