Midwest Fish & Wildlife Conference 2018

AUTHORS. Todd Wills, Michigan Department of Natural Resources; Darryl Hondorp, US Geological Survey

ABSTRACT. Fisheries managers have recognized the expanding ecological role of the invasive round goby Neogobius melanostomus in influencing population dynamics of both predatory and prey species throughout the Great Lakes. Accordingly, the ability to assess changes in round goby abundance and habitat use is important for the future management of Great Lakes fish communities. Bottom trawls, the traditional sampling gear used by fisheries scientists to assess the relative abundance of benthic forage species, have proven ineffective for sampling round goby because of both the species’ benthic nature and affinity for coarse substrates that cannot easily be trawled. This poses a problem for fisheries management, since failure to sample round goby in their preferred habitats may introduce significant bias into relative abundance estimates. Beam trawling is an alternative field sampling method that is suitable for use over coarse substrates, and could prove useful in reducing bias if round goby are consistently more abundant in hard substrates and are susceptible to the survey gear. Therefore, we assessed the effectiveness of a beam trawl for estimating the relative abundance of round goby by sampling a gradient of habitat types in Thunder Bay, Lake Huron. We deployed underwater cameras to capture still photos of round gobies and determine their presence/absence and relative abundance in each habitat type. Camera deployments were then followed by a single tow with a beam trawl, and relative abundance measures from both gears were compared. The beam trawl was successful at capturing young-of-year round goby (30mm TL), whose presence was confirmed by underwater photography, were difficult to capture. Video collected from the beam trawl during sampling suggests that sampling effectiveness for young-of-year round goby can be increased by an awareness of substrate composition and paying careful attention to vessel speed.