Exploring the population dynamics of Irish Sea plaice, Pleuronectes platessa L., through the use of Paulik diagrams

Abstract

Data from the ICES Virtual Population Analysis (VPA), for the years 1964 to 1994 were utilised to construct a life history model for plaice ( Pleuronectes platessa) of numbers of individuals from adult stock to numbers of recruits. The resultant four-panel graph is a Paulik diagram. The number of eggs produced for each stock size was calculated using published length-dependent fecundity relationships. The number of eggs produced was modified by the age structure of the stock. The overall mortality in the pelagic phase was dependent on the temperature regime during development. The eggs and larvae were subject to four models which describe mortality through the pelagic phase. The model outputs were the numbers of metamorphosing individuals on the nursery grounds. Daily mortality rates for the nursery ground phase were calculated from the difference between the numbers of metamorphosing individuals and numbers of recruits (from VPA). The models predicted daily mortality rates on the nursery ground of between 0.009 and 0.029 d −1. In all cases the estimated nursery ground mortalities were in close agreement with published results. All models suggest a strong positive relationship between the nursery ground mortality rate and the numbers of individuals metamorphosing on the nursery ground. A conceptual Paulik diagram for Irish Sea plaice is presented which incorporates density-independent mortality in the pelagic egg and larvae phases, and density-dependent or compensatory relationships in the nursery ground phase. In both cases colder temperature regimes lead to elevated recruitment for a given stock size.