Comparing Ship-based to Multi-Directional Sled-based Acoustic Estimates of Pelagic Fishes in Lake Superior

Abstract

Ship-based down-looking acoustic surveys are commonly used to determine the biomass and population density of commercially important fish species for resource managers and scientists, particularly in the Great Lakes and marine systems. However, there are some limitations and biases inherent in traditional down-looking surveys. I examined the use of multi-directional sled mounted acoustics equipped with up, side, and down-looking capabilities to overcome these limitations while examining the Lake Superior pelagic fish community. In the western arm of Lake Superior, I concurrently deployed the sled mounted acoustics during traditional down-looking surveys to directly compare the fish densities obtained from each gear, which I then followed with a mid-water trawl to inform my acoustic data with species composition. My findings from a two-way ANOVA showed a significant difference between fish densities detected by the sled-based survey and the ship-based down-looking survey indicating 60% of the pelagic fish community was missed by the traditional down-looking survey. This study also sought to provide a baseline for future research looking to discover which species in aquatic systems are most effected by traditional survey biases, as well as future work into using alternate forms of acoustic sampling to inform fisheries management and research.