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Survival after catch in trap-nets, movements and growth of the pikeperch (Stizostedion lucioperca) in Lake Hjälmaren, Central Sweden
Per Nyberg, Erik Degerman and Berit Sers
Annales Zoologici Fennici
Vol. 33, No. 3/4, PERCIS II: Second International Percid Fish Symposium Vaasa, Finland, 21—25 August 1995 (1996), pp. 569-575
Published by: Finnish Zoological and Botanical Publishing Board
Stable URL: http://www.jstor.org/stable/23736102
Page Count: 7
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Lake Hjälmaren is a shallow eutrophic lake with an intense commercial fishery. The pikeperch is the most important species from an economical point of view. A total of 2 299 individuals with a total length of 22—39.5 cm were marked with Dart tags during late June—early August 1990. The fish were caught in commercial trap-nets, measured, marked and released immediately at the place of capture. In total 1 900 recaptures were recorded and the number of recaptured individuals were 887 (38.6%). Six individuals were recaptured 20 times and one fish 39 times in trap-nets, before it was caught and killed in a gill-net. These figures show that the fishing is intense. 48% of the fish that were recaptured once and released were recaptured also a second time. They also show that the young pikeperch tolerate capture in trap-nets and also survive post-capture handling before the release quite well. The pikeperch showed a very stationary behaviour during the growth season and many individuals were captured repeatedly in the same trap-net, both during the season of tagging and following seasons. On average pikeperch smaller than 30 cm were caught less than 2 km from the point of release, whereas fish 35—39 cm on average were caught 4—5 km away during summer. In the autumn the pikeperch moved from shallower areas to the deeper central part of the lake and were caught in gill-nets in the winter-fishery. The average rate of growth of pikeperch in the size 25—30 cm at the time of marking was 51 mm/365 days until they reached 40 cm (legal size limit). After that, the size selective gill-net fishery significantly affected the average growth rate, by catching and removing the most fast growing individuals.
Annales Zoologici Fennici © 1996 Finnish Zoological and Botanical Publishing Board