Conservation, like beauty, is clearly in the eye of the beholder. The lack of a clear definition of what is meant by the term conservation, however, may encourage misconceptions about the degree to which biological objectives can be traded off against pressing economic and social objectives. Our purpose is to promote a dialogue about the meaning and practice of conservation, which might lead toward consensus on essential biological objectives. We present a brief history of the philosophical evolution of the term conservation and offer a definition of conservation based on the argument for an ecological ethic. This ethic requires that human benefits be derived in a sustainable manner and recognizes that human uses need to be reconciled with intrinsic and necessary ecosystemic functions and structures. We then present a preliminary set of operating principles applicable to the management of fish stocks that are consistent with an ecological or ecosystemic view of conservation. By proposing a set of conservation principles for fisheries management we hope to initiate a debate about just what those principles ought to be.

Commonest lake types of the 15 combinations of four fish species (walleye, Stizostedion vitreum vitreum; northern pike, Esox lucius; lake trout, Salvelinus namaycush and smallmouth bass, Micropterus dolomieui) were walleye–pike (22%), pike "only" (19%), lake trout "only" (16%) and smallmouth bass "only" (10%). Lake trout–walleye and lake trout–walleye–smallmouth bass types were extremely rare. Lake depth and area were variables of greatest significance in distinguishing lake types by discriminant analysis. Climatic factors explained the general geographic distribution of smallmouth bass. Hypotheses to explain the low frequency of walleye in small lakes include possibilities of (1) low probability of successful coexistence of pike and walleye, (2) lack of wind fetch to clear spawning areas, and (3) "Lebensraum requirement" of the walleye. Key words: limnology, Percidae, methodology, Ontario lake types, Stizostedion vitreum vitreum, Esox lucius, Salvelinus namaycush, Micropterus dolomieui, distribution, associations

We propose that the optimum habitat of the percid fishes Perca flavescens, P. fluviatilis, Stizostedton vitreum vitreum, and S. lucioperca in lakes may be defined by the littoral and sublittoral environmental conditions equivalent to those in large, temperate rivers. Analogous habitat conditions include sand or gravel substrate, low current velocity, reduced light penetration (Stizostedion spp. only), temperatures optimal for growth and reproduction, and well-oxygenated spawning substrates. The species' evolutionary origins and reproductive patterns also reflect their riverine ancestral habitat. Evidence in support of the hypothesis is derived from the diversity of papers contributed to the PERCIS Symposium. Key words: Percidae, habitat, theory, Perca, Stizostedion

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