Links
- Document: Report
- Download citation as: RIS | Dublin Core
Abstract
Acoustic surveys were conducted in late summer/early fall during the years 1992-1996 and 2001-2017 to estimate pelagic prey fish biomass in Lake Michigan. Midwater trawling during the surveys as well as target strength provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2017 survey consisted of 34 acoustic transects [711 km total (442 miles)] and 40 midwater trawl tows. Mean prey fish biomass was 7.99 kg/ha [38.9 kilotonnes (kt = 1,000 metric tons)], which was 46% higher than in 2016 and 35% of the long-term (22 years) mean. The numeric density of the 2017 alewife year-class was 27% of the time series average and 0.6 times the 2016 density. This year-class contributed 15% of total alewife biomass (4.4 kg/ha). In 2017, alewife comprised 55% of total prey fish biomass, while rainbow smelt and bloater were 32% and 14 % of total biomass, respectively. Rainbow smelt biomass in 2017 (1.0 kg/ha) was 29% of the long-term mean and increased for the second time since 2008. Bloater biomass in 2017 was 2.5 kg/ha and 32% of the long-term mean. Mean density of small bloater in 2017 (120 fish/ha) was 80% of the long-term mean. Biomass density of large bloater increased to 2.2 kg/ha in 2017. This remains much lower than in the 1990s but likely shows evidence of recruitment of small fish observed in the past 5 years. Although prey fish biomass remains low relative to the 1990s, it did increase in 2017. This increase, along with higher-than-average survival of two recent alewife year classes, are likely a response to reduced predation pressure stemming from a reduction in the abundance of Chinook salmon.
Study Area
| Publication type | Book chapter |
|---|---|
| Publication Subtype | Book Chapter |
| Title | Status of pelagic prey fishes in Lake Michigan, 2017 |
| Year Published | 2018 |
| Language | English |
| Publisher | Great Lakes Fishery Commission |
| Contributing office(s) | Great Lakes Science Center |
| Description | 10 p. |
| Larger Work Type | Report |
| Larger Work Subtype | Other Government Series |
| Larger Work Title | Complied reports to the Great Lakes Fishery Commission of the annual bottom trawl and acoustics surveys, 2017 |
| First page | 29 |
| Last page | 38 |
| Country | United States |
| State | Michigan, Wisconsin |
| Other Geospatial | Lake Michigan |
| Google Analytic Metrics | Metrics page |