Discriminating nursery grounds of juvenile plaice (Pleuronectes platessa) in the south-eastern Irish Sea using otolith microchemistry

Nursery grounds are valuable habitats providing sources of food and refuge during early life stages for many commercially caught marine fish. Distinguishing between different nursery grounds and identifying habitat origin using trace elemental concentrations in aragonite structures of teleost fish has proved valuable in fish ecology and fisheries. This study aimed to (1) compare chemical signatures (elemental fingerprints) within sagittal otoliths of juvenile European plaice Pleuronectes platessa sampled from known nursery habitats in the south-eastern Irish Sea and (2) assess their potential and robustness as natural tags for identifying nursery grounds for the putative south-eastern Irish Sea plaice stock. Otoliths from juvenile plaice (‘1-group’, 6 to 15 cm total length) were obtained from 8 nursery grounds in coastal areas off north-west England and north Wales (including Anglesey) between June and August 2008. Solution-based inductively coupled plasma-mass spectrometry determined the concentrations of 10 elements (Li, Na, Mg, K, Mn, Zn, Rb, Sr, Sn, Ba), with significant differences in otolith element composition observed between all nursery grounds. Cross-validation linear discriminant function analysis (CV-LDFA) classified fish to their nursery ground of capture (46.2 to 93.3%), with a total group CV-LDFA accuracy of 71.0%. CV-LDFA between regions (north-west England and north Wales) classified fish with 82% accuracy. The discrimination of juvenile plaice from all 8 nursery grounds within the south-eastern Irish Sea using otolith microchemistry offers significant opportunities in the development of future effective fisheries management strategies through understanding the supply of juveniles from specific nursery grounds and adult plaice in the south-eastern Irish Sea.