Seabird entanglement in gillnets: a global assessment

22 05 2013

Most of the time, when a dead bird is reported on a SEANET beach, we never find out what happened to it. Whether it’s a lack of resources to perform necropsies, or simply that no cause was evident at necropsy and no more extensive diagnostics could be performed, we often end up with unsatisfying partial answers. It’s the nature of the game, I’m afraid. But once in a while, a Seanetter comes upon a pile of waterlogged carcasses along a short stretch of beach. In many of those cases, necropsy is rewarding and the findings are consistent with drowning in fishing gear. We can never say with complete certainty what happened, except in cases where a bird is documented as its hauled up in the net, but we have seen certain signs in drowned birds that are consistent across events and across species.

Hauling in a gill net. Fish are usually caught by their gill covers but may be entangled in other arrangements too.

Hauling in a gill net. Fish are usually caught by their gill covers but may be entangled in other arrangements too.

Most of the time, the species involved in these sorts of events are Red-throated Loons. These birds forage near shore, swimming underwater in pursuit of fish. The most likely culprit in their drownings are near-shore gillnets–a veritable wall of mostly invisible monofilament that the birds don’t notice until its too late. While NOAA here in the U.S. stations marine observers on ocean-going fishing vessels to document bycatch of non-target fish and of marine mammals and seabirds, the near-shore fisheries are woefully under-monitored. We suspect that birds hauled up in such nets are tossed overboard and occasionally turn up in large batches on shore. It’s a difficult phenomenon to track and delineate, as evidenced by an ambitious review article in Biological Conservation. The study sought to identify particular species groups that are most susceptible to gillnet entanglement (think loons and alcids–razorbills, murres, etc) and also areas across the globe where those species are most likely to be severely impacted. Sub-polar and temperate regions (like most of SEANET territory) are high on the latter list. The study also documented some surprising findings, like that gulls, not generally thought particularly vulnerable to gillnets since they tend to feed on near the surface, are, in fact impacted as well.

A slew of Red-throated Loons found on Long Island. Gillnet entanglement was our suspicion here. (Photo by Peg Hart)

A slew of Red-throated Loons found on Long Island. Gillnet entanglement was our suspicion here. (Photo by Peg Hart)

The paper points out what we have been frustrated by for years–the lack of coordinated monitoring and documentation of bycatch in this fishery. By piecing together published and unpublished data from all over the world, these authors estimate a minimum of 400,000 seabirds are killed in gillnets each year, and they suspect the real number is considerably higher. As for what to do about it, the paper does not venture to make recommendations, but has pointed out some promising research into making the nets more visible to the birds, changing the depth at which they are deployed, or, in some cases, switching to another form of gear altogether, though in some cases this last method may only shift the problem to a new species group.

We’re glad this issue is gaining more attention throughout the world, and we will continue to try to do our part in documenting the extent of the problem here on the east coast.

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29 05 2013
More on gillnets: an inadvertent experiment | SEANET Blog

[…] close on the heels of last week’s post about estimated worldwide seabird bycatch in gillnets, an experiment that basically did itself. […]

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