Lake Ontario

Image Credit: Cameron Davis

The Benefits of Restoring Bloater

Bloater and other deepwater ciscoes (Kiyi and Shortnose Cisco) were extirpated from Lake Ontario by the mid-1900s, likely due to degraded water quality, predation by sea lamprey, interactions with invasive species (e.g., smelt, alewife), and overfishing. One of the key fish community objectives for Lake Ontario is to increase the diversity of prey fishes, including by restoring deepwater ciscoes, that support salmon and trout populations and fisheries. One advantage of restoring a native deepwater cisco is that unlike alewife, the dominant prey fish, ciscoes do not have high levels of thiaminase. Thiaminase is an enzyme that breaks down thiamine (i.e., vitamin B1) and can lead to poor reproductive success for salmon and trout that consume high levels of thiaminase via alewife. Another potential benefit of a more diverse prey fish community is that it could offer greater resilience to future species invasions and to a changing climate.

Reintroducing Bloater into Lake Ontario

Around 2010, it was determined that the deepwater cisco species that was most accessible for Lake Ontario reintroduction was bloater from Lake Michigan. Starting in 2011 and for many years thereafter, the U.S. Fish and Wildlife Service (US FWS) teamed up with commercial fishers in Wisconsin to capture Lake Michigan bloater between January and February when their gametes are ripe. Right after fertilization, eggs were transferred to facilities run by Ontario Ministry of Natural Resources and Forestry, New York State Department of Environmental Conservation, the U.S. Geological Survey, and US FWS. Together, these agencies worked over several years to improve methods to rear these deepwater fishes, including the development of broodstock.

Starting in 2012, the first 1,200 bloater (about 6 months old) were stocked into the New York waters of Lake Ontario. In 2013, another 22,497 were stocked. By 2014, all hatchery reared bloater were marked to be able to distinguish stocked bloater from any wild reproduced bloater in the lake. The number of bloater stocked each year has varied, but between 2012 and 2022, more than 1,800,000 bloater (including fingerlings, yearlings, and adults) have been stocked into Lake Ontario.

Evaluating Reintroduction Success

Evaluation of the survival of stocked fish has largely relied on the extensive, inter-agency prey fish monitoring surveys that annually occur during spring through fall in Lake Ontario. To date, 15 stocked bloater have been recaptured.

A rough estimate of population size in 2019 (following 197,931 bloater stocked in 2018) predicted between 11,000 and 45,000 bloater swimming in the lake. Another helpful component of the evaluation has been putting acoustic transmitters in stocked bloater to estimate survival and to describe dispersal and movement. Although survival of bloater with acoustic transmitters has been relatively low (i.e., <42% after 12 days), they have been documented to move more than 8 miles away from where they were stocked in only 24 hours.

Ongoing work in Lake Ontario is seeking new ways to improve the survival of stocked fish and to confirm that bloater spawning habitat in Lake Ontario is sufficient to support wild reproduction, which has not yet been documented.

To read more on bloater stocking efforts in Lake Ontario, see Klinard et al. 2020, Holey et al. 2021, and Weidel et al. 2022.

A bloater that was stocked into Lake Ontario and recaptured during a prey fish monitoring survey. One of 15 stocked bloater that have been recaptured since the reintroduction program began. Image Credit: Brian Weidel