STRUCTURAL DYNAMICS AND ECOLOGY OF FLATFISH POPULATIONS

The concept of structure in populations of marine fishes is fundamenta l to how we manage and conduct research on these resources. The degree of population structure ranges widely among flatfishes. Although we k now that large populations tend to be subdivided into local population s, based on morphological, meristic and reproductive characteristics, these data often conflict with evidence on genetic stock structure, du e to the scale and organization of movement within the metapopulation. Movement of individuals between local subpopulations and colonization events on a microecological scale are probably important to some flat fish populations. Dispersal of larvae is known to be a major factor af fecting population mixing. Some flatfishes have planktonic stages of l ong duration and for these species there is often, but not always, lit tle population structure; gene Bow sometimes may be limited by oceanog raphic features, such as eddies and fronts. At the juvenile stage disp ersal can result in colonization of underutilized habitats; however, f or flatfishes with strong habitat requirements. this type of event may be less likely when suitable habitats are fragmented. Complex populat ion structure has major implications for management, e.g. lumping harv ested populations with little gene flow can have detrimental local eff ects. Moreover, the issue of population structure and movement influen ces the interpretation of research data, where populations are general ly treated as closed systems. There is currently a strong need for a m ultidisciplinary approach to study fish population dynamics and the st ructure of their populations. This research should involve molecular g eneticists, population geneticists, animal behaviourists and ecologist s. Migration mechanisms, colonization and extinction events, gene Bow and density-dependent movements are subject areas of great importance to managing large harvested populations, but our understanding of them at ecological scales, at least for marine fishes, is at a rudimentary level.