PRECISION OF DIVING AND CANOE-BASED VISUAL ESTIMATES OF ATLANTIC SALMON (SALMO-SALAR) ABUNDANCE

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.