Biodiversity offsets – an efficient way of protecting seabirds?

by Rebecca Nesbit 

Each year, 7.2 million tonnes of fisheries catch gets thrown away as bycatch, including fish, turtles and birds.

Modifying fishing gear is a popular way of reducing this, and to a large extent it can often be effective. However, suitable modifications aren’t always possible, so preventing fishing in certain areas can be the only way to solve the problem. As I’ve blogged before, this brings its own challenges.

A recent paper in PLoS looked at options of biodiversity ‘off-setting’ for seabirds caught as bycatch, much in the same way that carbon offsetting is popular for plane travel. It’s widely acknowledged that this isn’t a long-term solution, but in the short term it may be possible to save more birds by putting money into conservation schemes than it would be by modifying equipment or creating exclusion zones.

Tuna and squid fishing in particular leads to a bycatch of albatross, petrels, and shearwaters which get caught on the hooks of longlines. However, these birds often face a far greater danger in their breeding grounds from invasive mammals, particularly rats and feral cats, which have decimated many seabird colonies. The problem is so severe that most vertebrate extinctions over the past six centuries have been caused by invasive mammals.

To test the idea of biodiversity offsets, this paper uses the example of the tuna fishery which stretches along the east coast of Australia. The main victims here are flesh-footed shearwaters. Possible solutions include only laying lines at night and weighting the lines so they sink out of reach more quickly. These have helped but they can’t eliminate bycatch, and they’re expensive, potentially dangerous to use, and hard to enforce. The authors point out that “like world peace, bycatch elimination cannot be achieved over night”.

The shearwaters are also facing threats in their island breeding colonies, including habitat loss, ingestion of plastic, and predation by rats.

Hopefully, better technical solutions to reducing bycatch will be available in a few years time, so rather than implement what we currently have available, it’s perhaps better to look to other conservation measures to give the shearwater population ‘breathing space’ until a real solution is found. Eradication of rats would benefit the whole island ecosystem, not just the shearwaters. In the example of the flesh-footed shearwaters, eradicating invasive rodents is at least 10 times more cost effective than closing areas of sea to fishing.

The way I see it is that, if I was given a pot of money to save seabirds I would spend it on saving the most birds possible. So if the fishing industry has money to use for conservation maybe it is best put to use on islands not boats. However, biodiversity offsets should be a way of saving more birds, not of saving money.

Another interpretation is, of course, that we shouldn’t eat tuna. It’s delicious, and I do miss it…

Pascoe S, Wilcox C, & Donlan CJ (2011). Biodiversity offsets: a cost-effective interim solution to seabird bycatch in fisheries? PloS one, 6 (10) PMID: 22039422