Updated 2020-04-20 14:25:01
Lake Ontario -> 2.0 Offshore Pelagic Zone Goal -> Offshore Pelagic Prey Fish Community
Reporting Interval
2014 - 2019
Area
Offshore
Meeting Target?
Meets
Indicator Trend
Downward trend
Confidence?
High
Maintaining or increasing populations and increasing species diversity of the pelagic prey-fish community, including introduced species and selected native prey-fish species.
During this reporting period pelagic prey fish abundance indices have declined and diversity indices are low but have remained unchanged. Alewife continue to dominate the pelagic prey fish community and their abundance is related to climate influenced reproduction, lake productivity, and predator abundance. Surveys suggest Alewife reproduction was below average in 2013, 2014, 2017 and 2018. Alewife reproduction tends to be low when Lake Ontario experiences below average water temperatures in spring and winter. Diversity continues to be low because a single species, Alewife, dominates the community.
Lake Ontario adult Alewife biomass index (kg/ha) based on the April bottom trawl survey, 1997-2019.
Lake Ontario Age-1 Alewife biomass index (kg/ha) based on the April bottom trawl survey, 1997-2019.
Abundance indices for Lake Ontario pelagic prey fishes based on bottom trawls in U.S. waters, 1997-2019. These four species are specifically mentioned in Fish Community Objectives related to diverse prey fish communities (Stewart et al., 2017). Trawls in Canadian waters not shown (2016-2019).
Methodology
Multi-agency (USGS, OMNRF, NYSDEC) collaborative bottom trawl surveys are the primary data source for interpreting FCOs related to Lake Ontario prey fish. The April or spring bottom trawl survey has been collaboratively conducted in April and early May since 1978. The survey changed bottom trawls due to excessive dreissend mussel catches therefore only data from a consistent gear type are illustrated here (1997 – present). The survey targets Alewife at a time when their winter behaviors place them on the lake bottom, which maximizes their susceptibility to bottom trawls (Wells, 1968). The survey is also used to index other prey fish relative abundances. Daytime trawling is conducted at fixed sites located along transects extending from shallow (~6m) to deep (228m) habitats. From 1978-2015 the survey sampled from 8–150 m in U.S. waters at 12 transects. Changes in fish depth distribution and the need for lake-wide information have resulted in survey expansion. Since 2016, trawls have generally been collected from 6–225m with sites organized in 20–23 transects or regions distributed around the lake.
Bottom trawl catches are separated to species, counted, and weighed in aggregate. Subsamples of all species are also measured for individual length and weight. Abundance indices are calculated from catches and trawl effort based on area-swept estimates from trawl wings and indices are not corrected for catchability. Annual mean biomass or density estimates are lake area-weighted from thirteen 20 m (66 ft) strata depth intervals and the proportional area of those depth intervals within the U.S. and Canadian portions of the lake. Prey fish community diversity is quantified using the Shannon index, based on trawl catch by weight (Shannon and Weaver, 1949). The diversity index is calculated based on biomass estimates of 8 species and includes: Alewife, Rainbow Smelt, Emerald Shiner, Cisco, Threespine Stickleback, White Perch, Gizzard Shad, and Bloater. Additional information on the surveys and results can be found in Weidel et al (2019).
Other Resources
Cochran, W.G., 1977. Sampling Techniques, 3rd ed. Wiley, New York, NY.
Weidel, B.C., Connerton, M.J., Holden, J.P., 2019. Bottom trawl assessment of Lake Ontario prey fishes, in: NYSDEC 2018 Annual Report, Bureau of Fisheries Lake Ontario Unit and St. Lawrence River Unit to the Great Lakes Fishery Commission’s Lake Ontario Committee. Albany, NY, p. section 12.
Wells, L., 1968. Seasonal depth distribution of fish in southeastern Lake Michigan. Fish. Bull. 67, 1–15.
Contributing Author(s)
- Brian C. Weidel - U.S. Geological Survey (USGS)
- Jeremy P. Holden - Ontario Ministry of Natural Resources and Forestry (OMNRF)
- Michael J. Connerton - New York State Department of Environmental Conservation (NYSDEC)
- Brian P. O'Malley - U.S. Geological Survey (USGS)