Predatory fish like trout and salmon seem to be facing a vitamin deficiency in Lake Ontario, and the culprit could be one of their prey fish species, the alewife.
Researchers noticed in fall 2014 that steelhead trout migrating in the Salmon River were acting abnormally due to seemingly poor vision; anglers were even reporting deaths. After investigating, officials found that these fish were suffering from thiamin deficiency.
Thiamin, also called vitamin B1, isn’t something the fish (or any animal) can make themselves. They need to get it from their diet, which includes invasive species like alewife, rainbow smelt, and round goby. Dr. Jacques Rinchard, associate professor at the State University of New York’s Brockport campus, said thiamin deficiency has been a major challenge to fisheries biologists and managers in the Great Lakes since the late 1960s-early 1970s when problems were first seen in salmon and trout species in Lakes Michigan and Huron. Alewives are not native to those lake systems, and eventually the deficiency was linked to the alewives the fish have been eating.
Alewives are a key part of the salmon diet, Rinchard said. “In Lake Huron when the alewife (population) crashed, we noticed natural reproduction of lake trout in the lake again, indicating a link between alewives and the thiamin deficiency.”
Steven LaPan, the Great Lakes Fisheries section head with the New York Department of Environmental Conservation (DEC), said alewives have an enzyme called thiaminase, which breaks down the thiamin in their systems. What causes the amount of that enzyme to change in alewives from year-to-year is unknown, LaPan said.
But the impact is clear. Some predatory fish species that eat alewives are unknowingly depleting the thiamin in their system, causing a vitamin deficiency. This was one of the major factors that led populations of trout and salmon to collapse in Lake Ontario when alewives started becoming more abundant: both species were eating more alewives and getting sick because of it (they also suffered from habitat loss, overfishing and invasive species like sea lampreys). To contend with the alewives, Pacific salmon like chinook and coho were stocked in the Great Lakes to control the alewife population and allow lake trout and Atlantic salmon to recover. The thiaminase affects them too, but not as severely.
Rinchard’s lab at SUNY-Brockport is working with the US Geological Survey and Cornell University to research the link between alewives and thiamin deficiency in Lake Ontario. Preliminary results should be available in early 2017.
Fishery programs can help offset the impact of thiamin deficiency. Eggs can be treated with thiamin baths at a hatchery to make sure the fry develop properly and are healthy – a process undertaken by the New York Department of Environmental Conservation (DEC). Naturally producing populations like lake trout or steelhead trout can’t be assisted like that, and alewife control efforts are the main way to help those species. It is possible to inject migrating steelhead with thiamin so that their eggs are healthy, but it isn’t a viable option for a system like Lake Ontario.
Another possibility is letting chinook and coho salmon slash the alewife population, similar to what happened in Lake Huron (though food scarcity also was an issue there). While that would be a boon to native fish populations, LaPan said the sport fishing industry in the area has found success with introduced Pacific salmon species, so managers can’t let the alewife get wiped out if they want to maintain that predator in Lake Ontario.
The thiamin deficiency doesn’t appear to be as severe across the entirety of Lake Ontario, either. LaPan said alewive tissue samples from the Niagara River, Rochester and Cape Vincent found a drop in thiamin amounts from the west end of the lake to the east. This is consistent with the fact that most nutrients entering the lake come from the Niagara River and are used as the water travels eastward.
New York DEC and Ontario Ministry of Natural Resources and Forestry are considering a 20 percent reduction in Chinook salmon stocking, but that is mostly to keep pace with an alewife population weakness after the excessively cold winters of 2013 and 2014, LaPan said. On the New York side of the lake, the state imposes catch limits on lake trout (two a day with size restrictions) and Atlantic salmon (one a day), while anglers can still get take a combination of three Pacific salmon species and steelhead. Ontario allows one Atlantic salmon to be caught per day and up to three lake trout for properly licensed anglers on its side of the lake. The province also allows up to five Pacific salmon species to be caught, and up to three steelhead trout.
USGS scientists Ross Abbett and Rich Chiavelli watch salmon swim into troughs at the New York State Salmon River Hatchery. Credit: USGS Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C. Editor's Note: This post was updated on Nov. 14, 2016, to correct the type of fish referenced in problems first seen in Lakes Michigan and Huron.