Does the US Endangered Species Act work?

The US Center for Biological Diversity has just released an important study assessing the success of the US Endangered Species Act: the primary piece of legislation to protect biological diversity in the US.

As the report states, the purpose of the Act is "to prevent the extinction of America’s most imperiled plants and animals, increase their numbers, and eventually effect their full recovery and removal from the endangered list. Currently 1,312 species in the United States are entrusted to its protection".

The report goes on to point out that:

Opinions abound on whether and to what degree the Act has accomplished its goals. Most are politically driven, some are anecdotal, and a few attempt to wring long-term implications out of short-term data which are simply not adequate to answer the most basic questions about the effectiveness of the Endangered Species Act. Are species population numbers increasing or decreasing in response to being placed on the endangered list? Is progress toward recovery consistent with or slower than the recovery period outlined in federal recovery plans? … while the Endangered Species Act has existed for 32 years, long-term population trend data have never been systematically gatherer and analyzed for a large, unbiased sample of species.

The study attempts to rectify that by presenting population trend data and narrative accounts for all endangered species that historically or currently occur in eight northeastern states.

The study's timing is good as the future of the Act is being debated and critics seem to take it as a given that it hasn't achieved its aims.

Their results suggest that the Act has been successful in achieving its objectives:

• No species has become extinct after listing.
• Most species have improved since listing, with 93% of species increasing or maintaining a stable population since listing.
• Seven of the 11 species whose recovery plans aimed for recovery by 2005 had been delisted or at least ‘downlisted’ (ie, downgraded from ‘endangered’ to ‘threatened’).

One limitation of the study in my view is the lack of a control group with which to compare these species. It would be very interesting to see how the recovery of listed species compares with the recovery of species which, while threatened, have not been considered sufficiently endangered to warrant protection under the Act. This would go some way to assessing whether protection under the Act in itself aids recovery or whether, for example, general environmental improvement from other causes has been more important in the recovery of these species. Similarly, it would be interesting to see data on how these populations were progressing before they were listed (presumably they weren't preforming well if listing was required).

Of course, a control group would add its own difficulties in interpreting the results as measures stemming from recovery plans under the Act (eg, habitat protection) could have spillover benefits for other (non-listed) species. And data on species whose position is less precarious may be harder to come by as these species have not been the focus of conservation and research attention.

As far as I’m aware, no similar study has been done to assess the success of the similar threatened species legislation that exists in each of the Australian states and territories. There have been assessments but they’ve been more the type that the report describes as politically-driven, anecdotal or short term. Such a study would be of great value in Australia.