Great Lakes prey fish populations declining
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EmailConference provides a cross-basin overview of status and trends from 1978 to 2015.
There were massive changes in the Great Lakes fish communities during the 20th century. During the early part of the century proliferation of sea lamprey, alewife, and smelt occurred. In the mid-20th century the collapse of native fish communities, such as lake trout and ciscoes occurred. In the late part of the century there was stocking of trout and salmon; the invasion and proliferation of zebra mussels, quagga mussels, spiny waterfleas, and round gobies; declines in Diporeia, alewife, and rainbow smelt; and the oligotrophication of Lakes Huron, Michigan, and Ontario because of low phosphorus inputs and the cropping of phytoplankton by quagga mussels.
Given this scenario, questions are asked on how similar or different are the changes in fish communities across the Great Lakes and what could be causing these changes? Michigan Sea Grant and Michigan State University Extension recently held an educational session at the Michigan Fish Producers Association Annual Conference. At the conference there was a presentation on this topic by Chuck Madenjian of the U.S. Geological Survey Great Lakes Science Center, which reviewed data prepared by his colleagues Owen Gorman and Brian Weidel.
Assessments of Great Lakes prey fish stocks have been conducted annually by the U.S. Geological Survey since the 1970s using bottom trawl surveys. The focus of the surveys has been on the prey species cisco, bloater, rainbow smelt, alewife, and round goby. Total prey fish (alewife, rainbow smelt, bloater, and cisco) biomass declined during 1978-2015 in Lakes Superior, Michigan, Huron, and Ontario, based on bottom trawl surveys.
Bloater biomass peaked between 1989 and 1992 in Lakes Superior, Michigan, and Huron but there was an overall decreasing trend in bloater biomass during 1989-2015 in Lakes Superior, Michigan, and Huron. Alewife biomass decreased in Lakes Michigan, Huron, and Ontario since the 1970s. Rainbow smelt biomass decreased in Lakes Superior, Michigan, Huron, and Ontario during 1978-2015. Round goby biomass increased in Lakes Michigan, Huron, Erie, and Ontario during the 1990s and 2000s, then peaked, perhaps even decreased somewhat, and appears to have leveled off in all four lakes. Further increases in round goby biomass are not expected.
Predation does not appear to be the primary driver of bloater dynamics. But, several fishery biologists have proposed that predation on young bloaters by piscivorous fish since 2005 has prevented a sustained increase, as measured by the bottom trawl surveys, in adult bloater abundance since 2005 in Lakes Michigan and Huron. Predation has been the primary driver of alewife dynamics in Lakes Michigan, Huron, and Ontario since the 1960s. Predation appears to be the primary driver of rainbow smelt dynamics in Lake Superior, but not in Lake Michigan. Round goby populations in Lakes Michigan, Huron, Erie, and Ontario now appear to be under some degree of predatory control.
Michigan Sea Grant helps to foster economic growth and protect Michigan’s coastal, Great Lakes resources through education, research and outreach. A collaborative effort of the University of Michigan and Michigan State University and its MSU Extension, Michigan Sea Grant is part of the NOAA-National Sea Grant network of 33 university-based programs.
