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HYDROACOUSTIC ESTIMATES OF ABUNDANCE AND SPATIAL DISTRIBUTION OF PELAGIC PREY FISHES IN WESTERN LAKE SUPERIOR
Citation:
Mason, D. M., T. B. Johnson, C. J. Harvey, J. Kitchell, S. Schram, C. Bronte, M. Hoff, S J. Lozano, A S. Trebitz, D. Schreiner, E. C. Lamon, AND T. R. Hrabik. HYDROACOUSTIC ESTIMATES OF ABUNDANCE AND SPATIAL DISTRIBUTION OF PELAGIC PREY FISHES IN WESTERN LAKE SUPERIOR. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, (31):426-438, (2005).
Impact/Purpose:
To assess the abundance and spatial distribution of pelagic coregonines and rainbow smelt in western Lake Superior
Description:
Lake herring (Coregonus artedi) and rainbow smelt (Osmerus mordax) are a valuable prey resource for the recovering lake trout (Salvelinus namaycush). However, their respective biomasses may be insufficient to support the current predator demand. In August 1977, we assessed the abundance and spatial distribution of pelagic coregonines and rainbow smelt in western Lake Superior by combining a 120 kHz splitbeam acoustics system with midwater trawls. Coregonines comprised the majority of the midwater trawl catches and the length distributions for trawl caught fish coincided with estimated sizes of acoustic targets. Overall geometric mean pelagic prey fish biomass ranged from 85 800 kg km-2, with the greatest fish biomass occurring in the Apostle Islands region (700 - 800 kg km-2), followed by the Duluth Minnesota region (190 kg km-2), with the lowest biomass occurring in the open waters of western Lake Superior (85 - 100 kg km-2). Biomass density calculated from arithmetic means (weighted by area using bootstrap methods) was generally an order of magnitude greater than estimates using geometric means, but followed a similar spatial pattern. Discrepancies observed between bioenergetics-based estimates of predator consumption of coregonines and earlier coregonine biomass estimates may be accounted for by our hydroacoustic estimates.