Tagging data for 5959 bass, Dicentrarchus labrax L., released around England and Wales between 1970 and 1984 have been compiled and analysed to show seasonal distribution patterns and implied movements of populations in the southern North Sea, the central English Channel and the south-west and west coasts. Juvenile bass appear to remain near their nursery areas throughout the year, whilst adults show extensive migrations between summer feeding areas and winter pre-spawning areas, which are specific to local populations. Straying occasionally occurs between populations, but only at the ‘adolescent’ phase, and for management purposes local populations may be considered discrete.

Pawson, M. G., Pickett, G. D., Leballeur, J. Brown, M., and Fritsch, M. 2007. Migrations, fishery interactions, and management units of sea bass (Dicentrarchus labrax) in Northwest Europe. – ICES Journal of Marine Science, 64: 332–345. A total of 4959 sea bass was tagged between 2000 and 2005 around the coasts of England, Wales, southern Ireland, and the Channel Isles to investigate whether movement patterns documented in 1987 have changed and to estimate the level of competition for sea bass between inshore and offshore fisheries. Most (54%) of the recaptures of adult bass (fish >40 cm) tagged inshore and made between May and October were within 16 km of the release positions. From November on, an increasing proportion was recaptured at least 80 km south or southwest of tagging sites. Bass tagged on offshore spawning grounds in March and April showed reciprocal movement, 75% of recaptures between May and October being at least 80 km from the release site. These observations reaffirm the hypothesis that adult sea bass may move considerable distances to offshore winter spawning areas, but there was little evidence of the spawning migrations between the North Sea and the western Channel that were observed in the early 1980s. Just 3% of the recaptures of bass >36 cm tagged in UK inshore fisheries were reported from the offshore pairtrawl fishery, whereas half the recaptures of bass tagged in that fishery were made inshore along the UK coast. When weighted by the respective catches, this suggests that the effects of management measures implemented in the UK inshore fishery are largely restricted to that fishery. A proposal for stock units for assessment and management of NW European sea bass fisheries is presented.

Morphometric data on bass, Dicentrarchus labrax L. (Pisces: Percoidei), sampled around the coasts of England and Wales between 1982 and 1990, have been analysed to elucidate seasonal patterns of feeding, body condition and gonad maturity. The somatic condition and fat reserves of bass in the Irish Sea and southern North Sea improved more rapidly during the spring and summer than in bass further to the south. In winter, however, fat reserves were higher and there was more food in the stomachs of bass caught in the western English Channel. The onset of maturity was related to fish length. Male bass became mature for the first time at 32–36 cm total length, but though many females showed signs of gonad growth at this size, no female <42 cm was found with mature (ripe or spent) gonads. Gonad development in adult bass of both sexes began in October and, from January until June, most males >36 cm had ripe testes. The period during which ripe eggs could be expressed from the ovaries of female bass was briefer, with spawning apparently peaking in April. It is concluded that the migration of adult bass to the north in spring and southwards and westwards in autumn has both growth and reproductive benefits related to sea temperature, and that the more limited movements of bass <42 cm, which remain in relatively cold, inshore waters in winter, results in an inhibition of gonad maturity in females.

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