2010 Status of the Lake Ontario Lower Trophic Levels

This report presents data on the status of lower trophic level components of the Lake Ontario ecosystem (zooplankton, phytoplankton, nutrients) in 2010 and compares the 2010 data with available time series. Lower trophic levels are indicators of ecosystem health [as identified by the Lake Ontario Pelagic Community Health Indicator Committee (EPA 1993) and presented in the biennial State of the Lake Ecosystem Conference (SOLEC) reports] and determine the lake’s ability to support the prey fish upon which both wild and stocked salmonids depend. Understanding the production potential of lower trophic levels is also integral to ecosystem-based management. Continued evaluation of lower trophic levels is particularly important for fisheries management, as the observed declines in alewife and Chinook salmon in Lake Huron in 2003 may have been partly the result of changes in lower trophic levels (Barbiero et al. 2009)

Recovery and Decline of Lake Whitefish in U.S. Waters of Eastern Lake Ontario, 1980-2001

The lake whitefish (Coregonus clupeaformis) was an important member of the native fish community and a valued commercial species in Lake Ontario. Lake whitefish were common in U.S. waters of the lake until 1965 and very abundant in Canadian waters through the early 1970s, although their numbers declined shortly thereafter. During 1975-1985, lake whitefish stocks remained depressed throughout the lake as a result of the combined effects of degraded water quality, overfishing, and predation. Rainbow smelt (Osmerus mordax) probably preyed on whitefish fry, and sea lamprey (Petromyzon marinus) preyed on adults. During 1985-1987, lake whitefish stocks began to recover in eastern Lake Ontario, and their buildup continued into the mid-1990s. Reasons for the recovery likely included control of the sea lamprey population and a reduction in the number of piscivorous rainbow smelt. By 1997, lake whitefish abundance had declined severely again; some fish appeared to have dispersed from the northeastern to the southeastern regions of the lake, and the depth of capture increased. We believe that the collapse of Diporeia spp. populations during 1992-1999 was responsible for the decline in the lake whitefish populations and the shifts in geographic and bathymetric distribution because lake whitefish fed primarily on Diporeia spp. After the collapse of Diporeia spp. populations, lake whitefish in southeastern Lake Ontario fed on Mysis relicta and quagga mussels (Dreissena bugensis). Changing from a diet of high-lipid Diporeia spp. to low-lipid dreissenids and foraging on Mysis relicta at lower temperatures are apparently hampering the rebuilding of lake whitefish stocks