Slipping on the metal deck, I step back quickly as the motorized reel hauls the fish net onto the Ontario Ministry of Natural Resources boat. Early-morning breath mists the air; gloved hands reach for frantic fish trapped in the net as it is being pulled onto the boat. We eye each fish as it is tossed into a plastic bin filled with ice. Scales are everywhere, sparkling like sequins.
Bin after bin is filled as we continue with the survey along the Lake Erie shoreline. Excitement increases a notch when a metre-long brown trout is added to the bin, but work must continue as the net full of fish is still being pulled onto the boat.
From this first sight, it seems apparent that the lake is full of healthy fish, and all is well. But science says not so. The fish of Lake Erie have changed dramatically, and there is cause for concern for the future.
In the bins, we can see numerous slimy brown fish with bulging eyes
wriggling across the crushed ice, each about a hands’ length. Those round gobies are the descendants of a handful transported from across the Atlantic Ocean just 15 years ago. Today, the Lake Erie round goby population is now in the billions.
The round goby is not the only unwanted immigrant to Lake Erie. Its fellow European hitchhikers, zebra and quagga mussels have spread throughout North America since their introduction in the early 1980s. Even now, scientists are wrangling with exponential increases of another European introduction, the tiny bloody-red Hemimysis shrimp, discovered in Lake Erie only a few years ago. Those unwanted invaders are out-competing many native species and are changing the food web dynamics by altering prey-predator relationships.
The costs due to impacts of invasive species are high. In 2008, researchers at the University of Notre Dame, Center for Aquatic Conservation, estimated that invasive species cost around $200 million US dollars a year in losses to commercial and sport fishing, loss of habitat and impaired access to the area’s water supply.
With the addition of new exotic species nearly every year, many seem to think that nothing can disturb the huge commercial walleye and yellow perch fishery, among the largest in the world. However, those fisheries are in steady decline for a while. The disappearance of the blue pike, a close cousin of the walleye, serves as a cautionary tale.
The native blue pike was a tasty expensive treat eaten by restaurant patrons along the Lake Erie shorelines until the 1960s. Due to overfishing and possibly due to increased contaminant exposure, anglers found they no longer were catching blue pike in Lake Erie or elsewhere. Ten years ago, Carol Stepien, a University of Toledo fish geneticist, reported at a meeting that a 37-year frozen specimen was merely a blue pike – walleye hybrid. This confirmed that there couldn’t be any blue pike in the lake. Whispered rumours and pickled specimens in dusty museum jars are the only clues that those commercially valuable fish species ever existed.
Those shifts were why we were excited to catch a prize brown trout this morning. Many of us did not realize that such a magnificent specimen is the direct result of stocking programs. Desirable species have been replaced and supplemented many times over. For example, lake trout nearly disappeared from the lake in the 1940s due to over fishing and other factors. However, through government efforts, the lake trout and its salmonid cousins has been re-stocked every few years, ensuring that a few trophy sportfish will be caught every year by lucky anglers, and the occasional scientist.
The Natural Resources ship returns to its Port Dover dock after a long day of collecting fish. We carry the cold bins full of fish back to the laboratory. The next day, the fish will be carefully weighed, processed and counted. Many fish will go into a freezer for genetic and chemical analyses which will eventually provide insights into the complex dynamics in the lake, including the invasions, stocking and disappearances of many species.
This survey is not the first one. Ontario Ministry of Natural Resources has been conducting similar surveys for the last 30 years. All this work has allowed Natural Resources scientist to build an immensely valuable database on fish and environmental conditions. The database allows us to determine changes in fish communities through time along Lake Erie’s shorelines and see if there are links with ongoing environmental changes. We can say with absolute confidence that the Lake Erie we see today is just not the same lake that existed 40 years ago.
Added: Link to scientific paper.
LM Campbell, R Thacker, D Barton, DCG Muir, D Greenwood && RE Hecky. 2009. Re-engineering the eastern Lake Erie littoral food web: The trophic function of non-indigenous Ponto-Caspian species. Journal of Great Lakes Research 35(2): 224–231. http://dx.doi.org/10.1016/j.jglr.2009.02.002