Conservation Biology, Pages 1144-1147, Volume 12, No.5, October 1998
Recently, Allendorf et al. (1997) proposed criteria intended to guide prioritization of Pacific salmon (Oncorhynchus spp.) stocks for conservation. The authors provide a good summary of several important aspects of extinction risk, and we agree with many of their points: (1) prioritization is useful and may help focus conservation efforts; (2) a two-pronged approach that identifies the relative risk faced by different populations and evaluates their significance is a reasonable strategy; (3) risks should be evaluated based on multiple criteria; and (4) specific threshold values for these criteria promote objectivity and can assist in decision making. We also recognize the considerable experience of the authors and the many important contributions they have made, individually and collectively, to the biology and conservation of salmon. We don't believe, however, that their prioritization method is entirely workable, and we are concerned that their criteria ignore some major conservation issues for Pacific salmon. We are also concerned that, no doubt unintentionally, their paper gives the mistaken impression that evaluating risk for salmon populations is a straightforward process. This is far from the case for two reasons. First, scientific understanding of processes leading to extinction is limited, especially for salmonids, which have complex life-history strategies and a potentially strong metapopulation structure. Second, as the authors note, the quantity and quality of data relating to risk is quite variable among Pacific salmon populations, with fundamental data on population abundance and trends lacking for many populations.
For the past several years, the Conservation Biology Division of the Northwest Fisheries Science Center has had the lead role within the National Marine Fisheries Service (NMFS) in evaluating the status of anadromous Oncorhynchus spp. with respect to the U.S. Endangered Species Act (ESA). The ESA listing process differs somewhat from the prioritization process Allendorf et al. discuss; for example, our evaluations focus on evolutionarily significant units (ESUs) of salmon, which are generally larger units than the "stocks" considered by Allendorf et al. Furthermore, instead of prioritizing ESUs according to relative risk, we focus on determining whether they are presently in danger of extinction or are likely to become endangered in the future-roughly the ESA's definition of endangered and threatened species, respectively. Still, the biological considerations defining risk and significance should be similar in the two processes.
Our comments focus on the assessment of extinction risk rather than other factors Allendorf et al. consider in developing their prioritization. We should emphasize that an important first step in developing a conservation framework is to identify biologically meaningful conservation units. This is a complex issue for Pacific salmon, for which individual spawning populations link into larger metapopulations, and groups of metapopulations form larger clusters (Waples 1995). There is no single hierarchical level that is always the most appropriate for focusing conservation efforts. The ESUs for salmon identified under the ESA are typically larger and more inclusive than the genetic diversity units or gene conservation groups identified under state plans in Washington and Oregon (Kostow 1995; WDFW 1997), but all three frameworks can contribute substantially to conservation. Local conservation efforts can focus on individual stocks, the only level considered by Allendorf et al. A comprehensive conservation program is unlikely to be effective, however, unless it also considers the relationships among the various hierarchical levels and their component populations. This perspective is largely absent from the paper by Allendorf et al.