Publication Abstract

Methods of assessing extinction risk in marine fishes

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

There has been considerable debate on the validity of applying threat criteria to marine organisms, as many species have large distributions, high fecundity, and large absolute population sizes, even after undergoing marked percentage declines. On the other hand, concern also has been raised that marine extinctions may be undetected at a variety of spatial scales. To address these issues we have compiled methods that have been used or may be used for assessing threat status of marine organisms. We organise the methods according to the availability of data on the natural history, ecology and population biology of species. There are three general approaches to inferring or assessing extinction risk: (1) correlative approaches based on knowledge of life histories and ecology; (2) time series approaches that examine changes in abundance; and (3) demographic approaches based on age- or stage-based schedules of vital rates and fisheries reference points. We consider trade-offs between precision of predictions from these methods and requirements for data that are often difficult to obtain. While many methods are well suited to species that have low productivity and are highly catchable, the theory is less well developed for assessing extinction risk in species that have small geographic distributions or narrow ecological specialisation. Comparisons of some of methods suggest that population decline criteria may be precautionary compared to more detailed population projection and time series approaches. We suggest that decline rates or threshold metrics should err on the precautionary side due to the combination of the reduced data quality associated with rare or declining populations and the uncertainty of determining the point where depensatory effects may occur or where recovery may be compromised by ecosystem or regime shifts.

Reference:

N.K. Dulvy, J.R. Ellis, N.B. Goodwin, A. Grant, J.D. Reynolds and S. Jennings (2004)  Methods of assessing extinction risk in marine fishes. Fish and Fisheries, 5: 255-275