Plaice on Irish and Scottish coasts: Contributions to the ecosystem-based management approach for pleuronectes platessa fisheries

Abstract

This study examines aspects of the early life history, growth and condition of plaice (Pleuronectes platessa) populations in Irish and Scottish waters, using innovative modelling approaches, among other techniques, to inform management and conservation efforts. Growth rate is an important determinant of a young fish’s survival and recruitment probability. A state space growth stanza/phase model was used to describe and quantify spatial variation in early life history traits and growth patterns of Irish and Scottish plaice at a regional scale and investigate possible drivers. Generally, these traits varied significantly at a regional level and although temperature accounted for some of the variation present, it was not the sole driver. Western Irish Sea fish had shorter larval durations, fewer cumulative degree days to settlement, higher larval and juvenile growth rates, post settlement acceleration and reached stable growth rates faster than west Irish or Scottish fish. A region independent positive correlation between larval and juvenile increment widths indicated that juvenile growth rates were somewhat pre-determined by larval growth. The feasibility of using variation in otolith microchemistry to discriminate between plaice from western Irish and Scottish nurseries was assessed. Sufficient variation was found to successfully classify fish on a regional and local scale, a tool for assessing population structure and connectivity. The dispersal of plaice larvae on the west coast of Ireland was modelled and the likely spawning ground identified. Larval behaviour, temperature mediated growth and hydrodynamic variability were found to greatly influence rates of larval delivery to nursery grounds. The impact of bottom trawling on fish condition was investigated. Condition effects appeared to be size and mobility related, with diet as a possible driver, although results were not conclusive. The study results are discussed in terms of their use to fisheries management.