Growth of bream, Abramis brama (L.), in Irish canals and implications for management

The growth rates of bream, Abramis brama (L.), were determined in three Iri sh Canals: the Royal and Grand Canals, and the Barrow Line. Compared with g rowth patterns for other Irish and European waters, the growth of bream was fast in the Royal Canal, but slow to moderate for the Grand Canal and the Barrow Line. Significant differences in bream growth in terms of both lengt h and weight were found between the three canal systems, and between canal levels, particularly in the Grand Canal. Associations between growth, and ( 1) alkalinity, (2) total fish biomass and (3) the ratio of bream biomass to total fish biomass were also found. However, it was considered that these three factors alone were not sufficient to explain the differences in growt h. Productivity was implicated as the main factor controlling bream growth because fish species diversity was greater and total fish biomass was gener ally higher in levels of the Grand Canal with faster growing bream populati ons. The division between 'fast' and 'slow' growing bream also corresponded with a change in the aquatic weed community. There is evidence to suggest that there was a corresponding change in macro-invertebrate community struc ture and density. Angler usage as another factor in promoting growth is dis cussed. The implications for the future management and development of these canals are outlined.