EFFECTS OF 5 YEARS OF INTENSIVE TRAWLING ON A PREVIOUSLY UNEXPLOITED SMELT STOCK

Citation
J. Horppila et al., EFFECTS OF 5 YEARS OF INTENSIVE TRAWLING ON A PREVIOUSLY UNEXPLOITED SMELT STOCK, Journal of Fish Biology, 49(2), 1996, pp. 329-340
Citations number
42
Categorie Soggetti
Marine & Freshwater Biology
Journal title
ISSN journal
00221112
Volume
49
Issue
2
Year of publication
1996
Pages
329 - 340
Database
ISI
SICI code
0022-1112(1996)49:2<329:EO5YOI>2.0.ZU;2-E
Abstract
In the years 1989-1993, over 1000 metric tons of fish (392 kg ha(-1)) was removed by trawls from the Enonselka basin in Lake Vesijarvi in or der to enhance the water quality. Roach(52%) and smelt (28%) were the most abundant species in the catches. In this study, the effects of th e mass removal on the previously unexploited smelt stuck was assessed. The total smelt catch was c. 282 metric tons. Due to the mass removal , the density of the stock collapsed from c. 46 000 fish ha(-1) in 198 9 to c. 14 000 fish ha(-1) in 1993 (M=1.0). The biomass of the stock d ecreased from 75 kg ha(-1) in 1989 to 12 kg ha(-1) in 1993. The age gr oup composition of the stock changed clearly towards the dominance of younger age groups. The male/female relationship in the samples change d from clear dominance of females to the dominance of males and the in fection rate by the sporozoan parasite Glugea hertwigi declined. The g rowth rate of the smelt did not change considerably during the years o f mass removal. The results suggest that in biomanipulated lakes sever al mechanisms may prevent the exploited stock from responding to the i ncreased mortality. (C) 1996 The Fisheries Society of the British Isle s