Oct 052017

 Threats loom but fish populations in the Kawarthas are still doing well

One of my most formative nature experiences as a boy was fishing with my grandfather at the family cottage on Clear Lake. The excitement of hooking into a large bass or walleye was unforgettable. Even at that time, however, he always insisted that I throw the fish back – something I did with great reluctance at the time. His conservation ethic has stuck with me ever since.

The Kawarthas is home to world-class fisheries. In fact, our lakes are the most heavily fished inland lakes in Ontario. Today, the sport fish community is composed of muskellunge, smallmouth and largemouth bass, walleye (pickerel), yellow perch, bluegill, pumpkinseed and black crappie. While walleye populations have declined, most other populations are doing well.

For management purposes by the Ministry of Natural Resources and Forestry, the Kawartha Lakes, along with Lake Ontario creeks and rivers to the south, are located in Fishery Management Zone 17 (FMZ 17). Roughly speaking, FMZ 17 extends from Lake Ontario, north to Dalrymple Lake in the west and across to Belmont Lake in the east. The zone includes 64 lakes greater than five hectares. Rice Lake is the largest. All of the Kawartha Lakes have similar fish communities because of their similar habitat and their connectivity via the Trent-Severn Waterway.

Lakes in the northern Kawarthas (e.g., Anstruther, Jack, Chandos) are not considered part of the Kawartha Lakes and belong to a different management zone (FMZ 15). The fish community is similar, however, with the exception that some of the lakes are also home to coldwater species like lake trout.

All of the lakes in FMZ 17 are classified as “warmwater”. A number of major warmwater rivers also flow through the area. These include the Otonabee, Trent and Crowe Rivers. Coldwater streams are generally limited to the Oak Ridges Moraine, which runs parallel to Lake Ontario. These streams support fisheries for migratory rainbow trout and salmon from Lake Ontario, as well as resident populations of brook and brown trout. Surprisingly enough, Harper Creek in Peterborough is also a coldwater stream and provides habitat for an endangered population of brook trout. The lakes within FMZ 17 offer very little in terms of coldwater fish habitat.

Historically, the sport fish population of the Kawartha Lakes and the Crowe River watershed consisted primarily of muskellunge, smallmouth bass, pumpkinseed (sunfish) and yellow perch populations. However, starting in the 1920s, walleye were intentionally introduced into all of the lakes. Largemouth bass and rock bass then spread into the Kawartha Lakes and Crowe River watershed, followed by bluegill (another sunfish) and black crappie. The latter two are native to the Trent River system. Northern pike have become established, via range extensions and/or unintentional introductions to the periphery of the zone, including Canal Lake near Kirkfield and Belmont Lake north of Havelock.

Walleye: Following their initial introduction, the Kawartha Lakes supported abundant walleye populations, which soon became the dominant predatory fish. By the 1980s, however, the lakes had undergone a series of significant environmental changes that altered the composition and structure of the fish community. These included a rise in both water temperature and clarity and a decrease in phosphorus concentration. Phosphorus is a necessary nutrient for both plants and animals.

Increased water clarity from the spread of zebra mussels has reduced the competitive advantage that walleye possess over other species in more turbid (murky) water conditions. Zebra mussels filter plankton from the water column, hence the greater clarity. Their presence has also decreased nutrients like phosphorus available to lower levels of the food chain. This has likely decreased the overall productive capacity of the lakes and created more favourable conditions for species like bass and muskellunge and less favourable conditions for walleye. As water clears, the amount of habitat for the light sensitive walleye is reduced and predation on young walleye is likely to increase. In lakes where bass are thriving, walleye tend to do more poorly. This is mainly because bass prey on young walleye.

Walleye decline continued through the 1990s, which was a decade that saw increases in new species such as black crappie and bluegill. Fewer large walleye in the lakes and rivers also means reduced predation of other species such as yellow perch, which feed on juvenile walleye.

Bass:  Overall, populations of smallmouth and largemouth bass in the Kawartha Lakes are considered healthy. The trends in their abundance are best explained by the ecology of each species and the habitat present in each lake. Some lakes, such as Rice and Pigeon Lakes, provide diverse habitat and are able to support abundant populations of both species. Other lakes, such as Balsam Lake, offer limited habitat for largemouth bass but do support abundant smallmouth bass populations. At the other end of the spectrum, lakes such as Chemong and Scugog provide a greater amount of shallow, vegetated largemouth bass habitat while smallmouth bass habitat is less abundant. Changes in water clarity, temperature and shifts in the predator community have also increased bass production. Climate change modeling predicts a dramatic increase in warmwater fish species, including bass.

Yellow perch:  Yellow perch populations are healthy and show successful and consistent reproduction. This species provides a critical prey base for a number of species, including walleye.

Sunfish and crappie: The abundance and distribution of bluegill, pumpkinseed and black crappie populations are best explained collectively, since these species are closely related and interact a great deal. Bluegills and crappie both compete with native pumpkinseed. The latter has undergone a gradual decline in abundance since bluegill and black crappie arrived and exploded in number. Now, bluegill abundance appears to have stabilized, but black crappie may still be increasing. Bluegill and crappie are now thriving in the northern Kawarthas, as well.

Pike and muskie:  FMZ 17 supports a healthy, high quality muskellunge fishery. This is likely attributable to the combination of suitable habitat and the absence of northern pike. Pike and muskellunge compete for both habitat and food resources, and muskellunge density is typically lower when pike are present. Northern pike are currently not present in the majority of waters in FMZ 17. However, as already noted, they are present around the periphery of the zone and moving downstream from the west. Pike have typically been managed as an invasive species due to concerns for muskellunge populations and disruption of lake ecosystems. While muskie populations are currently healthy, the potential invasion of northern pike to the Kawartha Lakes remains a serious threat.

Brook trout: Brook trout (speckled trout) are the only self-sustaining, naturally reproducing native salmonid (salmon, char and trout) species in FMZ 17. They are synonymous with high quality environments. However, they are now mostly limited to isolated, often low density, populations in streams on the Oak Ridges Moraine. These include Baxter Creek near Millbrook and Fleetwood Creek near Bethany. Their low abundance is explained mostly by habitat degradation and competition with brown and rainbow trout, both of which prey on juvenile brook trout. Brookies have experienced considerable losses across their native range in eastern North America.

Sustained by cold groundwater, Harper Creek in the south-west end of Peterborough is home to one of the few remaining wild brook trout populations in Southern Ontario. A research team recently tagged 20 of these trout and will be able to follow their daily and seasonal movements. This will provide a window into the life history of wild brook trout in an urbanized and severely threatened watershed.

Lake trout: Northern Peterborough County still boasts healthy lake trout populations. In Jack Lake, for example, a naturally reproducing population is present in Sharpe’s Bay. Water quality here is excellent, with oxygen present right to the bottom.  Deepwater sculpin provide much of the food base for these fish. Historically, Stony Lake also had a population of lake trout, but they are believed to have disappeared the late 1980s.

Brown trout:   Brown trout were stocked between 1920 and 1975 in many streams in order to diversify fishing opportunities. They are a resident fish, which means they complete their entire life cycle in the same stream. Like brook trout, they spawn in the fall. Brown trout out-compete their native cousins, particularly when rainbow trout are also present. Their competitive advantage is due to greater temperature range tolerance, more spawning flexibility and larger body size.

Rainbow trout:  The stocking of rainbow trout also began in the 1920s. Not only are the populations healthy and self-sustaining, but they are now the most dominant salmonid in most Lake Ontario tributaries. Since 1974, the spring rainbow trout run has been monitored at the Ganaraska fishway at Corbett’s Dam in Port Hope. The construction of the fishway in the 1970s provided access to upstream spawning and nursery habitat.

Atlantic salmon: Starting in the 1980s and 90s, Atlantic salmon were experimentally stocked in eight Lake Ontario streams, including Wilmot Creek and the Ganaraska River. The Ganaraska offers excellent juvenile habitat for Atlantic salmon. Once a dominant Lake Ontario species, they were extirpated by the late 1800s.

Chinook and coho:  Native to the Pacific coast, Chinook and coho salmon were stocked in Lake Ontario in the late 1960s to provide recreational angling opportunities and to establish a top predator salmonid species following the dramatic decline in lake trout abundance in the lake. The populations are now reproducing naturally. Every year in September, they can be observed jumping up the fish ladder at Corbett’s Dam in Port Hope as they move upstream to spawn. It’s quite a spectacle!

Next week, I’ll turn my attention to non-game and endangered species. I’ll also look at the many challenges that fish populations are facing in the Kawarthas.