Using archived otoliths to determine stock structure and early life history of plaice (Pleuronectes platessa L.)

Abstract

Plaice (Pleuronectes platessa) are an economically important flatfish in European waters. However, there remains much to be learned about the life history of this fish especially for the earliest stages. This chapter presents an analysis of temporal and spatial variation in two aspects of the early life history of plaice: length of the larval life and larval growth rate. Archived otoliths (earstones) from adult fish were used for the investigation. Samples were obtained from collections held by the Marine Institute in Ireland, Centre for Environment, Fisheries and Aquaculture Science (CEFAS) in England and the Animal Science Group in Wageningen University in the Netherlands.Three randomly selected year classes of plaice were examined; 1990, 1997 and 2001. Three areas in Western Europe were chosen for the investigation of spatial variability. These regions were based on international fishing divisions; ICES area Vila (Irish Sea), Vllb (west of Ireland) and IVb (North Sea). Otoliths were polished and image analysis conducted. Statistical analysis of the otolith microstructure revealed that there was no significant temporal difference in larval growth rate and duration over the ten year study period at any location. With regards to spatial differences, there was no significant difference between plaice from the Irish Sea and west of Ireland for both larval growth rate and duration. However, Vila (Irish Sea) and Vllb (west of Ireland) differed significantly from the North Sea plaice. Larval duration is shorter and growth rate is faster in plaice from Vila and Vllb. A possible link with sea temperature and food quantity is explored and the results are discussed in the context of climate change.