Everything from climate change to invasive species are threatening our lakes, rivers and fish populations
Slowly but steadily, the lakes and rivers of the Kawarthas are changing. The abundance and variety of fish populations are undergoing a transformation that could make them unrecognizable in a few short decades. This week, I’d like to provide an overview of some of these trends.
Climate change may be the single largest factor influencing the future of fish populations – not just in the Kawarthas, but across the planet. According to Climate Change Research Report CCRR-16, prepared by the Ministry of Natural Resources in 2010, most of the Kawarthas is expected to warm from an annual mean temperature of about 6.4 C (1971-2000) to approximately 7.7 C (2011- 2040), 9.2 C (2041-2070) and 11.4 C (2071-2100). Although annual precipitation is not expected to change significantly, extreme precipitation events will be more common as Windsor, Kingston and Hamilton learned this year. To put the change into context, in just 25 years the Kawarthas could have the same climate that Windsor does today. By the 2080s, it could feel like we’re living in present-day southern Pennsylvania.
Warmer temperatures and increased evaporation will lead to warmer lakes and rivers, lower water levels, altered stream flow patterns and decreased water quality. The structure of existing fish communities will also change, as the productive capacity for warmwater fish species (e.g. bass, muskellunge) is likely to increase, while coolwater fish species (e.g. walleye) will struggle to survive here. Changes to water temperature will likely alter the timing of fish migrations, as well as spawning and hatching times. These conditions will probably allow non-native fish like round gobies to thrive and out-compete native species for resources. There will likely be an increase in the types and abundance of other invasive species, too, such as zebra mussel, Eurasian water-milfoil, frog-bit and fanwort. Climate change will also compound the impacts of other stressors, including pollution, industrial development, dams and habitat loss. There’s a sobering article in the Globe and Mail this week (October 10) about how climate change is already having a multiplier affect by exacerbating human impacts – industrial activity, for example – on the Mackenzie River watershed.
Invasive species influence both the productive capacity of our lakes and the makeup of the fish community. Specific impacts are different for each invading species. Round gobies, for example, reduce fish diversity through competition with, and predation on, other fish species.
The spread of zebra mussels has increased water clarity as their feeding behaviour filters plankton from the water column. This, in turn, decreases the nutrients available to lower levels of the food chain, which reduces the overall productive capacity of a water body. The result is more favourable conditions for species like bass and less favourable conditions for walleye. These large-eyed fish evolved to live and hunt in more turbid water conditions. Therefore, when the water becomes clearer, walleye lose their competitive feeding advantage over other fish species.
Many fish diseases can also be considered within the context of invasive species. These include parasites, viruses and bacteria. For example, during the summers of 2007 and 2008, bacterial infections and Koi Herpesvirus (KHV) caused the deaths of tens of thousands of carp in the Trent-Severn Waterway. These were the first confirmed cases of KHV in Ontario. KHV disease is caused by a virus that affects only carp, goldfish and koi. Another disease, viral hemorrhagic septicemia (VHS), had big impact on muskellunge several years ago.
Overfishing, too, is a serious threat to certain fish stocks. Although it’s hard to quantify, anecdotal reports of people flaunting fish regulations are widespread. Population growth in southern Ontario and the completion of Highway 407 to Highway 115 will also increase the pressure on fish stocks as anglers from the Greater Toronto Area and beyond will be able to travel to the Kawarthas more easily.
We may already be seeing a number of these threats combining to reduce lake trout populations in the Haliburton area. There are now far fewer lake trout in most of the Haliburton lakes, and those trout that are caught are usually small. A number of factors appear to be in play: competition from thriving populations of warmwater species like rock bass and yellow perch; the arrival of northern pike into some of the lakes; increasingly warm water temperatures which, in summer, reduce the amount of deep water oxygen available to trout and, in the other seasons, disrupt reproduction; and greater summer and winter fishing pressure on many of the lakes.
Species at risk
The Species at Risk in Ontario (SARO) List is the official list of endangered, threatened, special concern and extirpated animals and plants in Ontario. The following fish are currently listed as species at risk in the Kawarthas and south to Lake Ontario.
1. Channel Darter (Threatened): A member of the perch family, the channel darter only measures three to seven centimetres in length. An isolated population still exists in the Trent River. They are threatened by soil washing into the river from nearby urban and agricultural areas and by invasive fish species.
2. American eel (Endangered): These long, snake-like fish once supported a multi-million-dollar fishery in Ontario. They have historically been documented in the Trent River and as far inland as Rice Lake. Despite its name, there is no actual proof yet that eels existed in Eel’s Creek. American eels are threatened by dams and other in-water barriers, which prevent access to feeding and spawning areas.
3. River redhorse (Special Concern) The river redhorse is a thick-bodied sucker with a prominent snout and a reddish tail fin. They have been documented in the Trent River. Like eels, they are threatened by dams, which inhibit spawning migrations. Increased siltation and water turbidity from farming and urban development are also a threat.
4. Lake sturgeon (Threatened): This long-lived species is the largest strictly freshwater fish in Canada. When European settlers arrived here, sturgeon occurred throughout the Trent River system. They may also have been present in the Kawartha Lakes, although this has not yet been verified. In recent years, this species has only been found in the Lower Trent River, where a spawning population exists at Dam 1 in Trenton. A large dead sturgeon was found south of Glen Ross in 2010. Historically, over-fishing was the main cause of population decline. Now, habitat degradation and the presence of dams pose the greatest threats. Please report any sturgeon sightings to the Ministry of Natural Resources.
The number of active anglers in Canada is decreasing. According to federal government recreational angling surveys, more than one in five Canadians fished for sport in 1975; by 2010 the number was about one in ten. This may be because over 80 percent of Canadians now live in cities and have fewer opportunities to get out fishing. The decrease in the number of kids who fish is especially acute, dropping from about 1.75 million in 1990 to less than 50,000 in 2010. As fewer people fish, there is less awareness of the depletion of fish stocks and less concern for the health of our lakes. As Alanna Mitchell writes in the current issue of “Cottage Life” magazine, “a whole fishing generation has gone missing.”
Although many of the threats affecting fish populations demand collective action by governments at a global level – climate change and invasive species for example – there are things that individuals can do.
1. If you are an angler, throw back any large fish you catch. It’s simple: large fish are a lake or river’s brood stock and critical to self-sustaining fish populations.
2. If you own property, leave shoreline vegetation and woody debris like large logs in place. If necessary, restore native plants. Trees and shrubs that shade the water are a boon to fish stressed by warmer lakes. Refrain from mowing the lawn to the water’s edge.
3. Speak out. Right now, for example, brook trout in Peterborough’s Harper Creek are threatened by the casino development and the Harper Road realignment. Let your councillor know that everything possible must be done to protect this population.
4. Take your kids fishing. A new generation of anglers will assure a strong voice for conversation.
5. Learn more about the fascinating lives of the fish themselves. One way to do this is by taking your family fish-watching. Lock 19 in Peterborough is a great location to see large schools of spawning walleye in April, along with abundant white suckers. Go to the downstream base of the lock in the evening and shine a flashlight into the water. Watch for the bright eye-shine from the walleye’s large eyes.
I also recommend visiting Corbett’s dam in Port Hope to see rainbow trout in the spring and salmon in late summer. Another great way to see fish is to slowly paddle along shallow shorelines in June to look for bass or sunfish nests. The fish sweep out circular patches and then guard the nests once eggs have been laid. Often, these nests are visible from docks. You might even want to invest in an Aqua-Vu underwater camera to watch live underwater footage of fish from a boat or the water’s edge. You can also take photos and videos. The camera provides a fascinating up-close glimpse into the private lives of fish. Go to http://bit.ly/2xwNFIt for a video of the camera in action.
As much as anything, protection of fish populations requires a critical mass of people who spend time outside on our lakes and rivers – whether it’s through fishing, fish-watching, canoeing or other nature-based activities – and who value these amazing ecosystems.