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I ftllr~\clorr f ... 19 '3g 07<:1'60 0:--- Comment Conservation Biology of Fishes FRED W. ALLENDORF Department of Zoology University of Montana Missoula, MT 59812, U.S.A. "I love any discourse of rivers, and fish, and fishing." lzaak Walton Tbe Compleat Angler The following three papers were presented at a sympo- sium 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 liv- ing 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 rock- fishes 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 pub- lications (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 rele- vant to all fish species. Some 70%. of all the wocld's fishes listed as endan- gered or threatened are native to North America (Ono, Williams, & Wagner 1983, page 218). In addition, only one out of 83 species from throughout the wocld listed as threatened or endangered by the u.s. Fish and Wild- life 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 ef- forts with fishes. Fishes present some unusual challenges to conserva- tion biologists because they are different from other vertebrates in a variety of ways. Their tremendous tax- onomic diversity is the first challenge. Almost exactly one-half of all vertebrate species are fishes (Mayr 1969). . Fish species occur in virtually every aquatic environ- ment 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, & Ut- ter 1987). Individuals within a single species of fish sometimes show enormous differences in size. For ex- ample, females from ten populations of Arctic char (Salvelinus alpinus) range in mean weight at first sex- ual maturity from 23 g to nearly 1,000 g Oohnson 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 differ- ences 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 genotypic- phenotypic relationship in fishes may be somewhat dif- ferent from what it is in other vertebrates. The ~ phenotypic variation, coupled with 10 heri 1Q. cates greater suscc:;ptibilitv to environment::.l furtnr<i: This difference is not surprising in view of the indeter- minate growth capacity of most fishes and the greater metabolic sensitivity to temperature of fishes in com- parison to birds and mammals. The cichlid fishes of the New Wocld and Africa prob- ably best demonstrate the challenges to conservation biologists resulting from the great taxonomic diversity in fish species and their unusual genotypic-phenotypic 145 Conservation Biology Volume 2, No.2, Juoe 1988