The Great Lakes are a source of natural abundance, but how do humans interact with this ecosystem and how can we receive this abundance in a good way? Shannon Fera, a graduate student in the Environmental and Life Sciences program here at Trent, is studying the affects of invasive mussel species on Great Lake Whitefish. Shannon presented her research for the Symons Seminar Series Wednesday, October 10. Arthur got a chance to talk with Shannon about the research and her experience of it beforehand.
Fera did her undergrad at the University of Ottawa in Biology and has gained experience in different sorts of ecology by working for The Ministry of Natural Resources and the Department of Fisheries and Oceans throughout her time in Ottawa. Aaron Dunlop and Mark Ridgeway from the Ministry of Natural Resources are her supervisors and have provided great support in obtaining grants and data. Fera’s research is paid for by a grant from the Great Lakes Fisheries Commission, so the bent is on how to manage commercial fishing of the Great Lakes.
“[C]ertainly I grew up eating the fish from the Great Lakes,” she says after confessing to be a vegetarian. “I was always really interested in ecology…[but] I just love doing the aquatic stuff.”
She is “basically looking at how invasive mussels—so, zebra mussels and quagga mussels—how they’re affecting the fish that are feeding in the Great Lakes” and “how that feeding behaviour has changed” in the post-“aquatic invasion” Great Lakes. She looked at how the Whitefish are growing, their rate of growth and where the Whitefish are in the water column (shallow water or deepwater) in order to determine if the invasive mussel species came in and ate up all of the Whitefish’s food.
”If you’re getting fish and chips somewhere in this area, where the fish comes from the Great Lakes, chances are you’re eating Whitefish.” There is nothing special about their silvery white colouration but Whitefish are “a species that [are] very important and very abundant” in the Great Lakes and make up about 50% of commercial fishing in the Great Lakes.
”It’s not that the population size necessarily has crashed; I don’t want to give you the wrong impression that way,” it’s that “each individual fish doesn’t have enough to eat and so they’re not growing at the same rate.” So this will have repercussions on future generations of Whitefish because eventually if the trends continue, Whitefish will not have enough body mass to reproduce and we may yet see a crash in the population.
Shannon does most of her work analyzing 50-year-old scale samples and doing stable isotope analysis: “Personally I’m mostly in a lab, which is unfortunate because I love being outside in the field.”
Using scales from the Whitefish, Shannon can tell what the growth rate of the population has been in the past and what their growth rate is post-invasion. “Using those scales, you can age them, sort of like a tree ring ageing… exactly like you’re looking at a tree.” The scales come from a sampling process called gill netting. This is where technicians drop nets deep into the water and leave them for 24 hours. Different sizes of nets will catch different kinds of fish. “[F]or the most part it is destructive sampling” and “unfortunately we do have to kill some.” Other fish sampling methods, such as electro-sampling (“which is a lot of fun”), cannot go as deep as needed to collect Whitefish. Commercial fishing also use gill netting, but when ecologists sample, they catch ”less than 1% of the population” of Whitefish in the Great Lakes.
Isotope analysis is ”a really interesting kind of analysis to find out where [fish] are coming from and what [they’ve] been eating.” Isotope analysis is looking at the different weights of isotopes within the same atom and the ratio between the different isotopic weights in an atom are quite unique. An example of the information that can be gleaned from this process is that you can see the ratio being different for shallow water populations of Whitefish as opposed to deep water Whitefish. “It’s an expensive process,” so sampling sizes cannot be as large as any scientist would hope in order to yield more verifiable results. Isotope analysis “can be done just about anywhere” and is used in archaeological analysis of human diet as well.
The “aquatic invasion” of zebra and quagga mussels began in the 80s and early 90s. The cause is said to have been ballast water from international freighters. When a ship used to enter a harbour (this practise is banned now), it would release canisters of water (ballasts). This is so that the weight of the ship remains consistent in the face of the shifting weight of the cargo coming on and off the ship. When the water is taken in, some of the creatures living in the water would stowaway and subsequently be released into the Great Lakes.
The invasion never reached the shores of Lake Superior, though. There is speculation as to why that involves Superior being colder, deeper and bigger in general so it has “not as much productivity.” So, less algae, less food for mussels. This has allowed for a natural control group of sorts because ”we can see a sudden drop in the isotope ratios and the growth rate of the fish that coincides quite clearly with when the mussels established in the lakes,” but ”we don’t see that drop in Superior.”
Invasive species have no natural predators so they are able to reproduce and take over very quickly. There are no feasible solutions when it comes to managing their population because that would involve either eradicating the Great Lakes coastline, introducing a predator, or having native fish species eat the mussels. Introducing predators causes more management problems than offers solutions and the mussels are not good for the native fish species to eat.
Because of this, Shannon recommends that we “let it be a lesson” and manage our own fishing practises. “The ecosystems have to find a balance” and this involves humans managing fishing practices in order to help that along.
