Individual growth of juvenile plaice ( Pleuronectes platessa L.) on a small irish sea nursery ground (Port Erin Bay, Isle of Man, UK)

Abstract

The individual growth rate of juvenile plaice ( Pleuronectes platessa L. was studied in Port Erin Bay, Isle of Man, between 1989 and 1993. All plaice larger than 85 mm were measured and tagged with individually numbered anchor tags and released. All recaptured fish were remeasured and re-released back into the bay. The tagging data were used to estimate the population size between May and April each year and the growth rate of individual fish. The growth of juvenile plaice in Port Erin Bay was compared to theoretical growth rates which were modulated by temperature alone or a combination of temperature and initial length. These data were also compared to population level growth rates calculated from changes in mean length per month from regular beam trawl series. A total of 2547 plaice larger than 85 mm were tagged with 435 recaptures. Over the sampling period there were minor differences in temperature between years. The population growth rate varied between 0.1 and 0.27 mm·d −1 whereas the individual growth rate varied between 0 and 1.67 mm·d −1. There were significant differences in growth rate both between seasons and between years. During the summer the individual growth rate was significantly higher than the models predicted. Low temperatures often coincided with high densities so that it was difficult to separate the effects of density and temperature on growth rate. At the individual level growth rate tended to be highest when the conditions on the nursery ground were optimal whereas at the population level there did not appear to be a simple relationship.