Carnage on the coast!

18 11 2014

The title here may be somewhat hyperbolic, but the situation on Gil Grant’s North Carolina beach on November 10 was striking. Gil found 7 dead birds, all of which had been thoroughly dismembered and stripped of flesh. For the most part, all that remained were wings and the occasional flayed skull. Six of the birds were laughing gulls, and one was a ring-billed gull.

ggrant6834-16287Whenever several specimens of a single species or closely related species turn up dead at the same time, we always have to consider a disease as a possible cause. But what else could it potentially be? Gil pointed out one likely suspect himself, writing this note on his report: “all 7 gulls today within 1/2 mile of fishing pier, gill nets, and shrimp boats.”

Nice clean skull, possibly thanks to ghost crabs.

Nice clean skull, possibly thanks to ghost crabs.

This is a situation we encounter a few times a year: a suspected case of bycatch, where birds are entangled and killed in fishing gear and then tossed aside. The diagnosis is not easy to make, however, even in fresh carcasses. When a bird is documented coming up dead in a net or other gear, the case is fairly clear. But we often get only a waterlogged carcass washing up on a beach, and it’s much harder to attribute those deaths to bycatch. The situation on Gil’s beach is further complicated by the heavy scavenging of these carcasses.

ggrant6826-16283This scenario is common–larger scavengers like other gulls pick the carcasses apart, and then, on southern beaches, it appears that ghost crabs do a thorough job of cleaning almost all the remaining flesh off the bones with remarkable speed. You can see a crab burrow near a carcass in one of these photos. We don’t see quite this much cleaning off of bones up here in the north, which, to me, is further support of my ghost crab hypothesis, since we don’t have them up here.

Because of the scavenging, there is no way to determine a definitive cause of death in these birds. But we have at least documented the presence of these several carcasses. I have been chatting with researchers interested in tracking bycatch and marine debris, and they are also interested in these more circumstantial cases, so we may soon be contributing photos from cases like Gil’s to that effort as well. You never know to what use your SEANET reports may be put in the name of conservation science!

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