The importance of comparative studies in stock analysis

The identification and discrimination of stocks of fishes lies at the inter esting juncture of fishery biology and fish microevolution. Fish have been "taken apart" in the search for features that discriminate between stocks. Early stock studies focused on morphological characters (meristic counts an d morphometric measurements) that are expressed phenotypically, and hence, benefit from incorporation of both genetic and environmental information, b ut suffer from the absence of information on their respective contributions . However, the ability to discriminate stocks has risen with the emergence of more sophisticated laboratory and statistical tools. Some of these techn iques are mostly sensitive to environmental information, i.e., microchemica l analysis of otoliths. Others are purely genetic (i.e., various forms of D NA sequence analysis), and reflect time, selection pressure, and the degree of isolation among populations. But despite this diversity of approaches, all are based on a common principle: the signal from the among-stock variat ion must exceed the noise of within-stock variation. Much of the uncertaint y concerning the application of stock concept approaches stems from the lac k of synchronicity in the development of the many potentially differentiati ng features between fish stocks. If so, then this field would benefit from a greater understanding of the trajectories of differentiation of analyzabl e features-gained from comparison between approaches from a microevolutiona ry point of view. Because only heterogeneity, and not homogeneity of fish s tocks can be demonstrated, and because sophisticated stock identification i s costly, it is imperative to select an appropriate approach from the outse t. Unfortunately, comparative studies among stock identification approaches have only rarely been conducted. Although this "black art" could continue to muddle along, there is no doubt that useful information on the relative sensitivities of stock analysis techniques would be gained via well-planned intercalibration studies. (C) 1999 Elsevier Science B.V. All rights reserv ed.