Publication Abstract

Migration history and stock discrimination in North Sea plaice through coupled analysis of otolith d18O and archival tag data

Migration history and stock discrimination in North Sea plaice through coupled analysis of otolith d18O and archival tag data

A. Darnaude and E. Hunter*

The otoliths of adult female plaice (Pleuronectes platessa L.) tagged with electronic data storage tags (DSTs) were examined for their potential to reconstruct stock structure and migratory history based on oxygen stable isotope composition. DSTs provide unprecedented data on in situ temperatures and fish movements in the wild, and previous studies of plaice in the North Sea have identified three geographically discrete feeding aggregations (sub-stocks) during the summer, from which the adults migrate to spawn during the winter. Otolith d18O values for 39 fish were obtained from the growth band corresponding to DST recording time using micro-milling and mass spectrometry, to assess the relationship between seawater temperature (as recorded by the DST) and otolith oxygen isotope ratio. To obtain accurate estimates of seawater d18O, simulations were made with the General Estuarine Transport Model (GETM) to predict salinity values for geolocated daily positions of individual fish, calculated from the DST pressure record using the tidal location method. Seawater d18O was then derived from water salinity using the salinity-d18O equation for the North Atlantic (Duplessy et al., 1991). This allowed accurate estimation of the relationship between seawater temperature and otolith oxygen isotope ratio. DST temperature records of 30 to 510 days from 150 tagged-fish were then used to predict δ18O experienced by plaice individuals in the wild. Average annual δ18O values were significantly different between the 3 plaice sub-stocks in each of the years 1997, 1998 and 1999. Retrospective identification of summer feeding location could therefore be achieved for each year studied based on δ18O values alone. Analysis of δ18O in the growth bands deposited prior to tagging showed that specimens belonged to the same sub-stock in each of the 3 years analysed, providing further evidence that plaice exhibit multi-year fidelity to feeding locations. The combined use of otoliths and electronic tags in this study illustrate how valuable additional life-history information can be obtained from electronic tagging studies that would not otherwise be easily obtainable using conventional fisheries techniques.

Reference

A. Darnaude and E. Hunter* (2007) Migration history and stock discrimination in North Sea plaice through coupled analysis of otolith d18O and archival tag data. Second International Symposium on tagging and tracking marine fish with electronic devices, October 8 - 11, Donostia, San Sebastian, Spain.

A. Darnaude and E. Hunter*

Second International Symposium on tagging and tracking marine fish with electronic devices, October 8 - 11, Donostia, San Sebastian, Spain.