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Evaluation of bottom trawls as compared to acoustics to assess adult Lake Herring (Coregonus artedi) abundance in Lake Superior

Journal of Great Lakes Research

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Abstract

We compared density estimates from day bottom trawl tows against night midwater trawl tows and acoustic gear to test the hypothesis that adult lake herring (??? 250 mm) are underestimated by day bottom trawl tows during the annual USGS spring fish community survey in Lake Superior. We found average density at nine nearshore stations was significantly higher at night (21.3 adult fish/ha) compared to day (1.0 adult fish/ha; p = 0.0119). At nine offshore stations, no lake herring were captured during the day but density averaged 39.6 adult fish/ha at night. At a lakewide scale (n = 18 stations), precision (relative standard error) was much better using night midwater trawls and acoustic gear (37%) compared to day bottom trawls (100%). Moderate sample size increases using the former methodology would likely bring precision within recommended levels (??? 30%) for stock-recruit data sets. Our results suggest that 1) population abundances of adult lake herring in Lake Superior are much higher than previously considered, 2) the annual spring fish community survey may not provide a relative index of abundance of adult lake herring, 3) night midwater trawls and acoustic gear are necessary for assessing adult lake herring abundance, and 4) previous studies using lake herring data from the annual spring fish community survey need to be re-evaluated in light of these results. Lake herring appear to become progressively more pelagic and less susceptible to bottom trawling as they mature. Day bottom trawls appear to be an adequate tool for estimating relative density of age-1 recruits, although this method still suffers from relatively poor precision.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evaluation of bottom trawls as compared to acoustics to assess adult Lake Herring (Coregonus artedi) abundance in Lake Superior
Series title:
Journal of Great Lakes Research
Volume
32
Issue:
2
Year Published:
2006
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Great Lakes Research
First page:
280
Last page:
292