A. Locke, PRECISION OF DIVING AND CANOE-BASED VISUAL ESTIMATES OF ATLANTIC SALMON (SALMO-SALAR) ABUNDANCE, Fisheries research, 29(3), 1997, pp. 283-287
Precision (repeatability) of visual counts of Atlantic salmon (Salmo s
alar L.) by divers and canoeists was evaluated in the Northwest Upsalq
uitch River, New Brunswick, in October 1995. Diver counts were more pr
ecise (coefficient of variation, CV 3.9-19.5%) than canoe-based counts
(CV 22.0-97.3%), Diver counts of large salmon were more precise (CV 3
.1-11.3%) than counts of grilse (CV 7.6-19.5%), probably because of di
fferences in fish behaviour. CVs of total counts were usually lower th
an CVs of grilse or large salmon counts, suggesting that observers var
ied more in their ability to correctly identify fish than in their abi
lity to locate fish. Diver counts provided a reasonably precise index
of abundance (95% confidence limits were within 16% of the mean in tri
als with three or more observers), but canoe counts were highly depend
ent on observer experience. (C) 1997 Elsevier Science B.V.