Professor John Casselman

How can we act to prevent invasive species and protect biodiversity in the Great Lakes? As part of our World Water Day series, Water Canada got scientific with Professor John Casselman of Queen’s University’s Biology Department.

Water Canada: In terms of biodiversity, how has Lake Ontario changed in the past fifty years? What kind of challenges does water quality present to biodiversity in the Lake?

John Casselman: The diversity of fish species in Lake Ontario has changed dramatically in the past 50 years. At the beginning of the period, the rate of disappearance of native species slowed, but saw the collapse of the cold-water fish community, particularly with the disappearance of the deepwater cisco, with the last kiyi caught in 1964. Although blue pike were not extremely abundant, they were locally common in various locations in the eastern basin until the late 1950s (e.g., Big Bar Shoal), with the last caught in the early 1970s.

Throughout the 1970s and 1980s, the greatly diminished species flocks of the cold-, cool-, and warm-water assemblages remained relatively stable. The virtual disappearance of the once very abundant American eel from the inshore waters was a particularly notable exception. Quite disconcertingly, biodiversity increased, primarily because of the steady and persistent appearance of invasive species. There are 185 non-native species in the Great Lakes Basin and new ones become established at an alarming rate every nine to twelve months.

Ballast water is a main vector, but canals, waterways, trade in live organisms, and aquaculture are also involved. Some species, such as the round goby, which appeared in the late 1990s, were subsequently associated with a new problem involving pathogens (e.g., botulism and viral haemorrhagic septicaemia [VHS]), the latter causing catastrophic die-offs of some native species: freshwater drum and muskellunge. It is now documented that in 2005 to 2006, a new strain of VHS appeared, which killed off 50 per cent of the spawning population of the well-managed trophy-size muskellunge of the upper St. Lawrence River.

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These invasive species destabilized fish communities because they are generally ill-adapted and go through “booms and busts”; e.g., alewife die-offs. An increased in species diversity associated with alien invasive species is certainly not a diversity to our liking. Any factor that results in environmental change, such as water quality, causes instability. Ecosystem and water-quality conditions that are less altered and more stable, pristine, and “historic” will enhance the status and well-being of a diverse native fish community.

WC: What are some of the actions that need to occur to encourage biodiversity in Lake Ontario? Will the upcoming national wastewater strategy have a positive effect on biodiversity?

JC: It is apparent that invasive species dramatically reduce native species diversity. This is best exemplified by the invasion of gobies in the inshore waters of Lake Ontario. This species has greatly reduced, and in some cases virtually eliminated, small native inshore species; e.g., various cyprinids. One relatively insidious effect is climate change. Increased temperature conditions are encouraging native warm-water species while reducing the abundance and diversity of cool- and cold-water species.

Everything that humans can do to reduce their carbon footprint will slow the rate of carbon dioxide production and warming and encourage cooler and more stable thermal conditions and a more diverse native fish community. Any factor that results in more stable and less variable environmental conditions will enhance species diversity, and of course, conditions that are more typical of historic environmental conditions will enhance biodiversity. It is essential that we try to reduce anthropogenic stresses. If water quality improves, so will species abundance and diversity.

WC: What’s the current situation with Asian carp? How badly has Lake Ontario been affected? How would a major infestation affect water quality and biodiversity? What are the challenges involved with Asian carp? How can we mitigate the problem?

JC: Just as dreissenids are expanding rapidly from the Great Lakes Basin throughout North America, “Asian carp,” composed of several species, are rapidly approaching the largest body of fresh water on the planet. These carp are non-native, having escaped from aquaculture in the southern United States and made their way through the Mississippi and Illinois rivers, becoming a major economic and ecological nuisance. They are now found throughout the southern United States and are threatening the Great Lakes.

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The primary pathway for the Asian carp to enter the Great Lakes from the Mississippi Basin is through two canals in the Chicago area: the Chicago Sanitary and Ship Canal and the Cal-Sag Canal. There is some evidence that they have entered southern Lake Michigan. They are able to spread rapidly, reproduce in large numbers, and become a predominant species in an ecosystem. Once established, there is little chance to control them. Like the sea lamprey, they will become a permanent element of Lake Ontario if they enter it. Since their escape nearly two decades ago, the bighead carp and the silver carp, which are plankton feeders, the former zooplankton and the latter phytoplankton, have overwhelmed the Mississippi and Illinois river systems. They were originally imported to control plankton in aquaculture facilities, and they can certainly do that, not just in these confines but in the whole-lake ecosystem. In some areas near St. Louis, they now represent 97 per cent of the fish biomass.

Their commercial value is much lower than that of native fish. They commonly reach a large size, over 20 pounds, and eat 40 per cent of their body weight each day. Their consumption of plankton greatly diminished and destabilizes a key source of food for both small and large native fish. In addition, the silver carp jumps when startled by noise and vibration and can cause considerable damage and human injury, even death, when they become “flying fish.” There is little doubt that the bighead carp and silver carp would have a significant negative impact on food webs by reducing the primary production essential for native fish species.

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What can be done if Asian carp enter Lake Ontario? Not much. We have no methods of control at the present time and nothing is in the foreseeable future. Our experience with control of lamprey and other invasive fish species indicates that prevention is key; eradication is not possible. There is now a concerted effort to try to “ecologically” separate the canal systems in a way that makes it impossible for the species to move from the Mississippi Basin to the Great Lakes Basin and vice versa. This action is urgently needed and is being sought.

It is apparent that a single invasive fish species can cause significant and permanent damage to the economic and ecological health of an aquatic ecosystem and negatively affect native species and their diversity. Control of invasive species, if at all possible, is expensive and ongoing; hence the key is prevention. There is no doubt that if silver carp become established, they can inflict harm directly on people; excited by vibration, they become a dangerous flying fish missile.

For those who understand that fish are important indicators and integrators in the aquatic ecosystem, it is particularly encouraging to see that fish are again leading the way in Canada’s recently proposed wastewater regulation, informing, as they did, concerning the role of increased phosphorus and contaminant loading, loss of biodiversity, and changing environmental and climatic conditions. As proposed under the Fisheries Act, these new regulations concerning the release of wastewater effluents are expected to reduce risks for human and environmental health and fishery resources.

On March 23, Professor Casselman will be speaking on Lake Ontario’s biodiversity at the Toronto Regional Conservation Authority’s second Lake Ontario Evenings event at the Gladstone Hotel. For details, click here.

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