Abstract
In an already funded project under Theme 1 we are investigating population genetic structure and population dynamics of the commercially important flatfish plaice (Pleuronectes platessa). In this new proposal we plan to conduct a parallel investigation involving the ray species Raja clavata. Because rays and flatfish are part of the same mixed fisheries, it is of interest to compare population structure in species with maximally different life history and dispersal characteristics. In sharp contrast to flatfish, rays are characterized by low fecundity, no pelagic larval stage, high survival rates of juveniles and very low dispersal. This is predicted to lead to locally discrete or patchy subpopulations/demes in which persistence of the larger metapopulation will depend on the size and connectedness of subpopulations. Comparison of dispersal processes (using direct tagging/recapture data) in relation to population structure (assessed using indirect, high resolution, genetic data) within the metapopulation provides a means to estimate gene flow, migration and effective population size. This information is critical to the design of management strategies in mixed fisheries where different species have overlapping food resources. A part of the research will utilize generic si,ulation models of metapopulation dynamics which are an important newer element relating spatial processes to fisheries management. Fluctations in population sizes, growth rates, migration and extinction are notoriously difficult to estimate. With the opportunity to combine direct and indirect estimates from the demographic and genetic data respectively, we can provide more realistic paramaterization for the model . The overall aim of the proposed project is to compare and contrast spatial population structure in low dispersal species such as rays with high dispersal species such as plaice; and to set the stage for extensive modelling (Round 3 of the NOW-prioriteit Program) that will utilize the total data to assess the consequences of various specific management scenarios in the context of sustainability.
Netherlands