The diel activity levels and spatial distribution of roach Rutilus rutilus differed markedly between two shallow lakes of different environmental state. The movements of roach (12-25 cm L T ), with surgically implanted mini-radio transmitters, were monitored regularly during several 48 h tracking sessions in a clearwater and in a turbid lake. In both lakes, the roach in general were most active during dawn and dusk and least active during the night. Activity level in midsummer was lowest around noon in the clear lake and high around noon in the turbid lake. In summer, roach in the clear lake stayed passively in a restricted area of water lilies during the day and moved into the central part of the lake during the night. In the turbid lake, roach were dispersed all over the lake during the day and moved close to the shoreline at night. Predator : prey fish ratios did not differ in the two lakes, however the observed behaviour of roach in the clearwater lake may be explained by a larger predation pressure from fish and birds, both being favoured in the clear water. # 2004 The Fisheries Society of the British Isles

No abstract

Biomanipulation, the reduction of planktivorous fish to enhance filter-feeding zooplankton, has been used to rehabilitate eutrophied lakes. However, efficacy and long-term success were dependent on nutrient load, lake morphometry and biomanipulation measures. The ongoing focus on sustainable use of aquatic resources offers the chance to perform lake rehabilitation using a combined strategy of nutrient load reduction and traditional inland fisheries management techniques. Particularly in Central and Western Europe where piscivorous fish are the target species of most commercial and recreational fisheries, an enhancement of the piscivores by stocking and harvest regulations may act successfully in the co-management of ecosystem and fisheries. Guidelines are presented on how biomanipulation can be used as in lake rehabilitation by considering the objectives and constraints of traditional fisheries management. Alternatives in the decision tree are elucidated by examples from

– This study investigated the habitat use of 0+ pike (9–17 cm) in relation to two different water transparency regimes (clear water/chlorophyll water), two different light regimes (day/night) and the presence/absence of prey using 16 m2 experimental ponds. Pike could freely choose between two structured habitats (a simple structured and a complex structured), an interface habitat (between the structured habitats and open water) and an open water habitat. Foraging success of the pike in relation to water transparency was investigated by comparing mean condition (Fultons K) of the pike as well as the number of surviving prey fish. Habitat use was influenced by the presence/absence of prey and varied between waters with different transparency. The presence of prey intensified the use of structural habitats of 0+ pike in both clear and chlorophyll waters. A preference for complex habitats was found in clear water and was presumably related to foraging. The pike in chlorophyll water, in contrast, appeared more evenly distributed among all habitats, as illustrated by a more intensive use of open water in chlorophyll water compared to the clear water. No detectable impact of water transparency on the foraging success of 0+ pike was found.

SUMMARY 1. Radio transmitters were implanted in large perch (27–37 cm) in a shallow lake in Denmark. Between 6 and 13 perch were tracked every 3 h for 24‐h periods twice (summer) or once a month (winter) from August 1997 to July 1998. Activity levels were recorded as minimum distance moved per hour. 2. No significant differences in activity levels of individual fish were observed. 3. Highest activities were observed at daytime with peaks at dawn and dusk or midday. This diel pattern was most pronounced from October to April, whereas diel variations were less in the summer months, with no peaks occurring in midsummer. The general lack of activity at night supports the idea that perch is a visually oriented forager. 4. There was no significant relationship between daytime activity during the year and temperature or day length, but nighttime activity was correlated with temperature. In contrast with previous findings, activity levels varied little seasonally, except for high activity levels that occurred concomitantly with high temperatures in August. Instead, we found a significant relationship between the total distances moved per day and temperature, indicating that perch moved at the same average speed in the wintertime, but did so for shorter periods than in summer because of shorter day lengths. 5. Diet of the tagged perch shifted from fish dominance between August and January to invertebrates from February to June. There was no correlation between the diet shift and activity levels, indicating that feeding on invertebrate requires similar activity levels as predation on fish. 6. The results of this telemetry study throughout a year suggest that perch are more active during the winter than previously inferred from gill‐net catches. This observation underscores the importance of perch as a predator of 0+ planktivorous fish in lakes and has potential implications for pelagic food web structure and lake management by biomanipulation.