The scientific implications of the EU Project WESTHER (Q5RS - 2002 - 01056) to the assessment and management of the herring stocks to the west of the British Isles

No abstracts are to be cited without prior reference to the author.

WESTHER’s overall goal was to describe the population structure of herring stocks to the west of the British Isles, to enable the production of a set of improved guidelines for the conservation and management of biodiversity and stock preservation by incorporation of the findings into the assessment processes for western herring. Analysis of a multi-disciplinary suite of characters was carried out on herring collected from spawning aggregations, from nursery areas and from adult non-spawning, feeding aggregations in the study area. The results revealed temporally distinct spawning grounds in the area, with each of them being populated by a group of herring which, in general, have a certain level of site fidelity. There was a clear distinction of many of the different juvenile samples. There was, however, strong evidence that juveniles from separate spawning areas mixed in some of the nursery areas sampled. There was also evidence to suggest mixing of adults from separate spawning components, especially in the area to the west of Scotland (VIa North). The science, therefore, suggests links between the areas, with fish spawning in different areas mixing, to varying extents, on feeding grounds and, therefore, fish from each spawning aggregation do not remain discrete on their feeding grounds. The results from WESTHER suggest that under the current stock assessment units, two basic assumptions of stock assessment (the stock is a closed unit, and the data used in assessments are representative of the entire stock) are violated. Alternative recommendations for the combination of stocks are discussed with reference to their assessment and management.