Evidence of bowhead whale feeding behavior from aerial photography
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Evidence of bowhead whale feeding behavior from aerial photography

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Evidence of bowhead whale feeding behavior from aerial photography
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    Aerial photographs of the Bering-Chukchi-Beaufort population of bowhead whales (Balaena mysticetus) were analyzed to investigate their feeding habits, particularly epibenthic feeding near Barrow, Alaska. The analysis was based on mud visible on the dorsal surface of whales, resulting from feeding near the seafloor. A new photographic scoring system was developed and tested by bowhead experts, including subsistence whalers, to ensure an acceptable level of agreement on the analytical method. The tests resulted in> 93% agreement when whales were scored as muddy, and 100% when clean. Over 3,600 photographs were analyzed from 1985, 1986, and 2003-2007, including photos from surveys in spring and late summer and in both the Western and Eastern Beaufort Sea. Of all the photographs analyzed, 64% were scored as definitively muddy. In spring, ratios ranged from a low of 27% in 2003 to a high of 76% in 2004. In May of 1986 and when all four May sample sets off Barrow were combined, there was a significant difference (t-test, P <0.004) between the proportion of muddy juveniles to the proportion of muddy adults, with muddy adults being more common. Tests in a flow tank demonstrated that mud can persist on bowhead whale skin for up to half a day, making it difficult to pinpoint where feeding occurred. Plots of whale sightings show that the Barrow area was a commonly used feeding ground during migrations in both the spring (61% of the sample were feeding, of which 55% were feeding epibenthically) and autumn (99% of the sample; 97% epibenthically). Epibenthic feeding in areas where petroleum extraction is underway with the risk of oil spills could have severe ramifications for bowheads.
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