Conservation Biology of Fishes

The following three papers were presented at a symposium on the conservation biology of fishes at the Society for Conservation Biology meeting in June of last year. The first paper presents problems special to species living in rivers; the second paper discusses desert fishes; and the final paper considers one of the most popular sport fishes of North America, the cutthroat trout. A fourth paper on the genetics of exploitation in rockfishes was presented at the symposium by Keith Nelson but is not included in this issue. Three or four papers are obviously not sufficient to provide a comprehensive overview of the conservation of a taxon with over 20,000 species that last shared a common evolutionary ancestor some 400 million years ago (Mayr 1969). Those interested in broader aspects of fish conservation may consult the following recent publications (FAO/UNEP 1981; Fetterolf 1981; Meffe 1987; Ono, Williams, & Wagner 1983; Ryman 1981). The three papers in this issue are concerned primarily with freshwater fishes native to North America. Nevertheless, all three papers stress general principles that are relevant to all fish species. Some 70% of all the world's fishes listed as endangered or threatened are native to North America (Ono, Williams, & Wagner 1983, page 218). In addition, only one out of 83 species from throughout the world listed as threatened or endangered by the U.S. Fish and Wildlife Service (Federal Register 1987) is a marine species. It is unclear how much the predominance of freshwater fishes from North America on such lists is due to the fishes per se and how much is due to the geographical distribution of ichthyologists. Nevertheless, the topics of these three papers reflect current conservation efforts with fishes. Fishes present some unusual challenges to conservation biologists because they are different from other vertebrates in a variety of ways. Their tremendous taxonomic diversity is the first challenge. Almost exactly one-half of all vertebrate species are fishes (Mayr 1969). Fish species occur in virtually every aquatic environment on the water-planet: lakes, streams, rivers, vernal pools, desert springs, estuaries, the open ocean, deep oceanic trenches, and underneath the polar icecaps. Fish also show much more intraspecific phenotypic variation than most other taxa (Allendorf, Ryman, & Utter 1987). Individuals within a single species of fish sometimes show enormous differences in size. For example, females from ten populations of Arctic char (Salvelinus alpinus) range in mean weight at first sexual maturity from 23 g to nearly 1,000 g (Johnson 1980). However, the larger phenotypic variation within fish species is apparently not associated with greater genetic variability. Heritability is the proportion of the total phenotypic variation that is due to genetic differences between individuals. Heritabilities for such traits as body length and weight are generally much lower within fish populations than within populations of other vertebrates (Allendorf, Ryman, & Utter 1987). These comparisons suggest that the genotypicphenotypic relationship in fishes may be somewhat different from what it is in other vertebrates. The high phenotypic variation, coupled with lower heritabilities, indicates greater susceptibility to environmental factors. This difference is not surprising in view of the indeterminate growth capacity of most fishes and the greater metabolic sensitivity to temperature of fishes in comparison to birds and mammals. The cichlid fishes of the New World and Africa probably best demonstrate the challenges to conservation biologists resulting from the great taxonomic diversity in fish species and their unusual genotypic-phenotypic