Publication Abstract

Comparison of threat and exploitation status in north-east Atlantic marine populations

N.K. Dulvy, S. Jennings, N.B. Goodwin, A. Grant and J.D. Reynolds

1. Threat listing of exploited marine species has been controversial because of scientific uncertainty about extinction risk, as well as the social, economic and political costs of management procedures that may be triggered by designation of species as threatened with extinction.

2. Here, we apply three extinction risk criteria to seventy-six exploited marine fish and invertebrate stocks. Two of the criteria are based on decline rates: World Conservation Union (IUCN) criterion A and the American Fisheries Society thresholds (AFS). The third criterion is based on population viability (IUCN criterion E), which is tested with a simulation model and two diffusion approximation methods.

3. We use a framework derived from signalling theory to assess the extinction risk outcome (threatened or not threatened) against the exploitation status of each stock as reported in fish stock assessments (inside or outside safe biological limits). For each combination of threat and exploitation we assessed the rate of hits, misses and false alarms.

4. Our analyses suggest that decline rate criteria provide extinction risk categorisations consistent with more quantitative population viability analyses, including simulation and diffusion approximation approaches, when applied to exploited marine species.

5. None of the extinction risk metrics produced false alarms. The quantitative IUCN E metrics both produced higher hit rates than the decline rate metrics (IUCN A, AFS) and all of the metrics produced similar miss rates. However the IUCN E methods could only be applied to some of the stocks and IUCN A decline rate criteria would be more widely applicable.

6. The extinction risk metrics and decline rate thresholds explored provide warnings of population collapse that are consistent with those provided in stock assessments.

7. Our results suggest that scientists with different backgrounds and objectives should usually be able to agree on the stocks for which the most urgent management action is needed. Moreover, IUCN decline rate metrics may provide useful indicators of fish stock status when the resources needed for full stock assessment are not available.

Reference:

N.K. Dulvy, S. Jennings, N.B. Goodwin, A. Grant and J.D. Reynolds (2005)  Comparison of threat and exploitation status in north-east Atlantic marine populations. Journal of Applied Ecology, 42(5): 883-891