Rodent Offsets?

You’ve heard of carbon offsets – you might pay a little extra for an airline ticket, for instance, so that they money can be used to plant trees that would soak up, or offset, the carbon emissions you’re creating. But how about “biodiversity offsets”? In a provocative proposal, three researchers suggest that requring commercial fishers to pay for efforts to eradicate rodents on land may do more for endangered seabirds than simply stopping fishing so the birds don’t get entangled in nets – at least in the short run.

Many proposals for biodiversity offsets have received “severe criticism,” Sean Pascoe and Chris Wilcox of Australia’s CSIRO research agency and C. Josh Donlan of Cornell University in New York write in PLoSONE. Often, that’s because such tradeoffs don’t force those buying the offsets – such fleets that are overfishing a fish stock or damaging coral reefs – to undo the damage they are doing. Establishing offsets to compensate for seabird by-catch, for instance, doesn’t stop the birds from being killed in nets. Still, the trio wondered if offsets might not have a role to play in some areas.

To find out, they studied the economics and operations of Australia’s lucrative tuna and billfish fishery, which also kills thousands of seabirds each year. Simply banning fishing or forcing fishers to use bird-safe technology would be the easiest solution, they note. “However, like world peace, bycatch elimination cannot be achieved overnight. If the technologies currently existed to eliminate seabird bycatch then no doubt they would be in place already, at least in some fisheries. Further, technology alone cannot solve the bycatch problem without effective enforcement and governance also being in place.” But biodiversity offsets, they argue, could offer a cost-effetive “stop-gap” measure “to provide initial relief for at least some seabird populations,” they argue.

That’s because some birds don’t face threats just at sea, but also on land from rodents and cats. Indeed, they note that “three-quarters of seabirds listed by the IUCN are threatened by invasive species, compared to 47% threatened by fisheries bycatch.”The researchers explored what would happen if – instead of simply stopping fishing – captains offset their bird kills by paying for rodent eradication efforts on nearby nesting grounds.

After crunching the numbers for a 40-year forecast, they found that “invasive rodent eradication is at least 10 times more cost effective than area closures.” Conservation benefits, they found, “could be achieved at lower cost if the fishing industry funded the rat eradication through a bycatch levy, for example, rather than ceased fishing in the area. Such a levy would also have the additional benefit in that it would create an incentive for fishers to avoid bycatch of seabirds, and could also provide funds for research into new fishing gear to further mitigate the problem.”

Offsets don’t “solve the actual bycatch problem,” they concede. But they “may provide breathing space for both the seabird species and the industry to find longer term means of reducing bycatch.” And offsets, they add, have the potential to “provide an opportunity to constructively address a global conservation concern, and forge an alliance between conservation and fisheries organizations.”David Malakoff | November 1, 2011


Pascoe S, Wilcox C, Donlan CJ (2011) Biodiversity Offsets: A Cost-Effective Interim Solution to Seabird Bycatch in Fisheries? PLoS ONE 6(10): e25762. doi:10.1371/journal.pone.0025762

Image © Marina Maslennikova |