Recruitment success of roach varied dramatically between 1979 and 1982 in Alderfen Broad, a small lake in eastern England. When fry were abundant (in 1979 and 198 1, but not in 1980 or 1982) the summer zooplankton became sparse and was dominated by copepods and rotifers. In years of good recruitment, as each of the preferred cladoceran prey species entered the diet of underyearling roach, its density dropped dramatically. Mean size of Daphnia hyalina and Ceriodaphnia quadrangula also declined significantly during these seasons. The results of enclosure experiments indicate that the link between roach recruitment and zooplankton dynamics is causal. Older roach also feed to a significant extent on zooplankton, but the 0+ age group exerted the greatest influence. The abundant underyearling roach in years of good recruitment showed poor growth, as a result of depression of their prey populations. Older fish also grew poorly in these years and were then less fecund in the following season. The evidence indicates that there may be a 2-year cycle in roach recruitment, and we describe the unusual circumstances in Alderfen which may be responsible.

Commercial fishing is one of the most important human impacts on the marine benthic environment. One such impact is through disturbance to benthic habitats as fishing gear (trawls and dredges) are dragged across the seafloor. While the direct effects of such an impact on benthic communities appear obvious, the magnitude of the effects has been very difficult to evaluate. Experimental fishing‐disturbance studies have demonstrated changes in small areas; however, the broader scale implications attributing these changes to fishing impacts are based on long‐term data and have been considered equivocal. By testing a series of a priori predictions derived from the literature (mainly results of small‐scale experiments), we attempted to identify changes in benthic communities at the regional scale that could be attributed to commercial fishing. Samples along a putative gradient of fishing pressure were collected from 18 sites in the Hauraki Gulf, New Zealand. These sites varied in water depth from ∼17 to 35 m and in sediment characteristics from ∼1 to 48% mud and from 3 to 8.5 μg chlorophyll a/cm3. Video transects were used for counting large epifauna and grab/suction dredge and core sampling were used for collecting macrofauna. After accounting for the effects of location and sediment characteristics, 15–20% of the variability in the macrofauna community composition sampled in the cores and grab/suction dredge samples was attributed to fishing. With decreasing fishing pressure we observed increases in the density of echinoderms, long‐lived surface dwellers, total number of species and individuals, and the Shannon‐Weiner diversity index. In addition, there were decreases in the density of deposit feeders, small opportunists, and the ratio of small to large individuals of the infaunal heart urchin, Echinocardium australe. The effects of fishing on the larger macrofauna collected from the grab/suction dredge samples were not as clear. However, changes in the predicted direction in epifaunal density and the total number of individuals were demonstrated. As predicted, decreased fishing pressure significantly increased the density of large epifauna observed in video transects. Our data provide evidence of broad‐scale changes in benthic communities that can be directly related to fishing. As these changes were identifiable over broad spatial scales they are likely to have important ramifications for ecosystem management and the development of sustainable fisheries.

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The behavioural basis of prey selection by underyearling bream (Abramis brama (L.)) and roach (Rutilus rutilus (L.)) SUMMARY. A clear difference in the ability lo escape from fish predators exists between members of the Cladocera and Copepoda. The results of our laboratory studies have shown that underyearling roach and bream both found copepods more difficult to capture than cladocerans. However, bream were far more efficient than roach at catching the more elusive copepod prey. The basis for this difference was the greater strike ability of bream, most likely related to its more protrusible mouth. In their natural environment the two species of fish exhibited food resource partitioning with planktonic Cladocera predominating in roach guts and copepods and non-planktonic Cladocera composing the vast tnajority of the gut contents of bream. Differences in diet are partly due to their contrasting attack abilities. Additional variation may arise because of subtle differences in the timing and location of foraging.