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Cost‐effective survey of fish by the intensive netting of a linear canal in the Midlands (UK)
Author(s) -
Smith P. A.
Publication year - 2006
Publication title -
water and environment journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 37
eISSN - 1747-6593
pISSN - 1747-6585
DOI - 10.1111/j.1747-6593.2006.00027.x
Subject(s) - netting , perch , fish <actinopterygii> , environmental science , fishery , toxicology , population , mathematics , statistics , biology , demography , sociology , political science , law
The performances of two micromesh nets, which were physically similar but differed in weight of leadline (i.e. 120 g/m 2 vs. 250 g/m 2 ), to estimate the numbers of four species of fish (roach, gudgeon, perch and bream) were investigated on 51 occasions. These two nets were found to capture fish longer than 25 mm. Capture efficiency was found to vary according to design of net, species and size of fish. Both nets usually produced a reduction in numbers of fish caught with successive removals, although the heavy leadlined net was more likely to cause a reduction in catch and in a constant manner than the light leadlined net. The accuracy of the heavy leadlined net to estimate a known number of roach ≥90 mm and gudgeon ≥90 mm was tested on two occasions. The known number was within the 95% confidence limits of the population estimate for both species, although the precision of the estimate for gudgeon was low at one site. The precision of the within‐site estimates was found to vary according to the type of net, the species and size class, and the number of removals. Overall, the heavy leadlined net was found to be more useful but required greater manpower. The implications of these findings for survey design are discussed.