Great Lakes Fishery Commission

Updated 2024-11-22 14:19:36

Lake Superior -> 2.0 Prey Species -> Offshore Percent Indigenous Prey Biomass

2.1.2 Percent of indigenous prey biomass greater than 95% for offshore waters of Lake Superior

Seventeen prey fish species/groupings, of which 14 are indigenous and three are non-native, have been captured during the USGS annual offshore bottom trawl survey. Principle prey fish captured during this survey (i.e., > 5% of the catch by number) include deepwater sculpin (indigenous) and kiyi (indigenous). Non-native species captured during this survey are rainbow smelt, ruffe, and alewife, but the cumulative catch of these species since 2011 is 59, 2, and 1 fish total, respectively.

During the 2017-2021 reporting period, prey fish communities were greater than 95% indigenous in offshore benthic surveys during 2017-2020 (Figure 1). No offshore benthic survey was conducted during 2021.

Confidence in this metric is medium because the bottom trawl gear is effective for only two of three principal offshore prey species: deepwater sculpin and kiyi. Cisco are also common offshore, but occupy open water, thus, are underrepresented in bottom trawl samples. Offshore midwater trawl sampling has shown that rainbow smelt are exceedingly rare in this portion of Lake Superior.  

Figure 1. The percent of fish, by mass, captured during USGS benthic surveys in offshore waters that are indigenous. The horizontal reference line indicates the target value of 95%.