Gray seals: the North Sea's great whites?

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Science  05 Dec 2014:
Vol. 346, Issue 6214, pp. 1196
DOI: 10.1126/science.346.6214.1196-d

Harbor porpoises with missing bellies first appeared on Dutch beaches in 2006; soon, dozens of mutilated porpoises began mysteriously and gruesomely washing ashore each year. Now, Leopold et al. have cracked the murderers' identity: gray seals. Photographs and autopsy results of more than 1000 stranded porpoises from 2003 to 2013 revealed torn blubber, scratch marks, and canine teeth marks—all pointing to seals. Finding the smoking gun—seal saliva DNA in the wounds—seemed impossible, as seawater should wash it away. But the team did find seal DNA at the bottom of deep narrow bite marks on three porpoises. Humans may be to blame for the change in seal hunting targets: With rising gas prices, fishermen switched from trawling to cheaper nets anchored to the seabed, which can also trap porpoises. The seals may have stumbled onto them and then gone on to hunt this larger, fattier prey.

Proc. R. Soc. London ser. B, 10.1098/rspb.2014.2429(2014).

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