A bass tagging project on the south coast of Anglesey, 1971-5, yielded 86 recoveries from 912 taggings. In addition to expected local movements a systematic pattern of seasonal migration was identified for adults. Fish present in summer moved to south Cornwall for the winter, returning in succeeding summers for spawning. Departure was normally before mid-October. Fish present after that had summered further north (reaching Furness in warm summers). These too moved south as winter advanced, though possibly not reaching Cornwall. A few solitary fish - unfit specimens or members of weak year-classes - appeared to remain through the winter. No evidence was found of movement to, or intermingling with stocks of, the Irish coast; nor, with one exception, the mainland coast of Europe. There was also no indication of movement eastward along the south coast: suggesting discrete populations there from those on the west coast. Juveniles (under 6 years) conformed broadly with the adult pattern but moved much less widely until they neared maturity. Early-winter concentrations of juveniles in the estuary on which the project was centred peaked, as in other estuaries, at age 4-plus: a stage at which they are particularly exposed to over-exploitation. Details are given of year-class strengths, growth-rates, sex-ratios and spawning. The project originated in growing concern for the future of this scarce and slowgrowing species, considered the most important sport-fish in U.K. waters and providing recreation for more than a quarter million anglers. The movement pattern identified shows that benefits of conservation measures applied in U.K. will not (on the west coast at least) be significantly eroded by emigration. Figures are given to illustrate the growing pressure on the species, and the serious decline in angling catch-rates over the past three decades - due largely to increased pressure, rather than to falling recruitment. To protect the species at its most vulnerable stage (age 4-plus) the present size-limit of 26 cm needs raising to 36 cm. Ways of improving the effectiveness of future tagging projects are suggested. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.
