Oct 122017

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

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

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.

Fishing pressure

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.

Fewer anglers  

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.







Jan 142016

Unbeknownst to most, a small but aggressive invader is lurking in the tranquil waters of Little Lake. For the time being, however, it seems to have met a roadblock in its attempt to expand and plunder waters to the north. The round goby (Neogobius melanostomus) is an invasive, bottom-dwelling fish that was first found in North America in the St. Clair River in 1990. Native to Eurasia, it is believed to have arrived in the ballast water of transoceanic ships. The goby has spread through all five Great Lakes and is now invading inland waters, including the Trent-Severn Waterway. Dr. Michael Fox and his colleagues at Trent University are doing important research on gobies and may have discovered evidence that the Trent-Severn invasion has been stopped. Where, you might ask? Right at Peterborough’s iconic Lift Lock.


Round gobies are small fish, measuring up to about six inches (16 centimetres) in length. They have a blunt snout and a large, frog-like head, which gives them the appearance of a tadpole. They can be distinguished from all other Ontario freshwater fish by a pair of fins on the underside of the body that are fused together to form what looks like a suction disk. The tail fin is scallop-shaped, and the brown to olive body is covered with prominent, dark brown spots.

Adult Round Goby in hand - Special to the Examiner

Adult Round Goby in hand – Special to the Examiner


The goby’s diet consists mostly of invertebrates found on lake and river bottoms. Mussels, in particular, are relished. These include invasives like zebra and quagga mussels, as well as native freshwater mussels. Many of the latter are species at risk. Gobies ingests zebra mussels whole, crush them with their teeth, and discard the shells before the soft body of the mussel is swallowed. Eating zebra mussels is not without negative impacts, however, and is linking the gobies to botulism type E. Botulism kills fish-eating birds like ducks, gulls, grebes and loons. The disease is caused by a toxin that is produced by the bacterium Clostridium botulinum. It is suspected that zebra and quagga mussels are ingesting the botulinum bacteria (invertebrates are not affected by botulism) and concentrating the toxins in their tissues. It appears that the toxins are then passed from zebra mussels, to gobies, and finally to fish-eating birds. A large percentage of dead birds in the Great Lakes that test positive for botulism have gobies in their stomach.

Gobies have another troublesome habit. They eat the eggs and young of other fish. This makes them a serious threat to native fish populations, including game fishes. Most affected, however, are native bottom-dwelling species such as logperch, mottled sculpins, northern madtom and the eastern sand darter. Madtoms and sand darters are listed as species at risk in the Great Lakes Basin. Gobies also compete with native fish for food and spawning habitat. Being larger and more aggressive, they take over prime spawning sites traditionally used by small-bodied native species. They also lay more eggs than many native fish and spawn more frequently. To make things even worse, gobies are at an advantage in killing prey, since they can hunt in total darkness. Gobies are so successful that divers have found up to 100 fish per square metre of lake bottom in parts of the Great Lakes.

Trent Research

Much of the research on the round goby has been carried out by scientists at Trent University, including Michael Fox, Jacob Brownscombe and Masters student, Chelsea May. In research done in 2009 and 2010, Fox and Brownscombe were able to identify some of the variables of goby range expansion. For instance, they observed rapid range expansion during the non-reproductive season. These “pioneer” gobies tended to be smaller individuals and most often females when compared to gobies at other range locations. The newcomers also exhibited more of a preference for rocky bottoms at range edges than in areas where a goby population has existed for longer periods. It appears that range expansion occurs when some of the gobies are forced from occupied areas by competition with others of the same species. They therefore migrate in search of alternate, high quality habitats.

A Trent study led by Emily Myles-Gonzalez, now a Masters student at Guelph University,  found that certain gobies are predisposed to exhibit behaviors associated with dispersal (moving into new territories) such as boldness, a higher resting metabolic rate and even a predisposition to “explore”. Gobies such as these are more likely to be located along the invasion front – “to boldly go where no goby has gone before” – than at a location where the species has been established for a longer period of time. It’s almost as if the bold and brash gobies are up at the invasion front, while the more laid-back individuals are happy to stay home.

Devin Fischer (left) and Chelsea May pulling a seine net in the Trent Canal. - Special to Examiner

Devin Fischer (left) and Chelsea May pulling a seine net in the Trent Canal. – Special to Examiner

Invasion thwarted?

Gobies in the Peterborough area have been able to advance to just above Little Lake but no further. The front has been stationary for two years. According to Fox, this may represent the first time a goby invasion front has been stopped in its tracks. There is no indication that the fish have advanced upstream past this point, either in the Canal or in the Otonabee River. Chelsea May and her team carried out extensive searches using seine nets, minnow traps and angling, even as late as November, 2015. However, not a single round goby was found above Lock 20 at Little Lake.

The apparent containment is probably due to a combination of an artificial barrier, namely the dam on the Otonabee River at London Street, and water management practises in the Canal. While there is no barrier in the Canal as such (gobies can pass through locks), the water level below the Lift Lock is lowered in winter to prepare the Canal for skating. A lower winter water level means less low dissolved oxygen for the fish to breathe. Gobies may be unable to survive in these conditions, unlike some of our native species like pumpkinseeds. As part of May’s Masters research, she will be testing gobies in the lab to see how well they tolerate hypoxia (low oxygen). It may be that low oxygen levels are forcing any fish in the canal at freeze-up to retreat back into Little Lake to overwinter. Asked why the gobies aren’t passing through the Lift Lock in summer, Dr. Fox said that small numbers may indeed get through, but not enough to establish a reproducing population.

 You can help  

Once round gobies are introduced to a new location, they can expand on their own. This may happen inadvertently when anglers use gobies for bait and then release them live in waters they do not yet inhabit. This is the most likely scenario for future goby expansion in the Trent-Severn Waterway. It is important to never buy or use round gobies as bait and never to release baitfish of any kind into lakes and rivers. If you find a round goby in the wild, please contact the toll-free Invading Species Hotline at 1-800- 563-7711.