Lake trout in Ontario are getting smaller and fewer, and when I asked John Casselman if that mattered (since they don’t seem to be in danger of disappearing altogether) his answer surprised me, because it focused as much on us as it did on them.
As a top of the food chain predator, lake trout are important in maintaining healthy lakes, he said. But we also need them in large enough numbers to sustain fishing, because when people fish, « sooner or later they end up respecting nature. » Unfortunately, the stresses on lake trout are so severe, fishing may have to be restricted.
Casselman is senior research scientist at the Ontario fisheries centre at Glenora on the Bay of Quinte. He’s concerned that, as people crowd into cities and towns, they distance themselves from nature, and find themselves « living outside the web. » He thinks fishing breaches that isolation.
He’s right, of course. In the days when I used to fish, I think I spent more time watching the life around me than I ever did trying to coax that big, old speckled trout out of the pool at the foot of the rapids. Like others, I discovered that I, too, had a place within nature’s web.
And so now I share a mutual sense of loss as Casselman describes the quadruple threat faced by lake trout in areas of the Canadian Shield south of Kirkland Lake. Bass are encroaching on their territory; rising temperatures are reducing their habitat; their reproduction rate is dropping; and fewer of their fry that hatch are surviving.
Lake trout are cold water fish. They require temperatures below 15° Celsius, which means that for six months of the year — from late spring until late fall — they stay deep in lakes. In mid-November, when lakes have cooled, they come inshore to spawn, and throughout the winter and early spring, they roam at all depths.
However, rock bass and smallmouth bass have been invading their lakes. They are warm water fish, and during the warm months, when trout are down deep where it’s cold, they prey on the same small fish favoured by the trout.
This leaves the trout with less prey during the winter when they roam surface waters, and so they rely much more on zooplankton, tiny organisms about the size of grains of sand. With less protein-rich diets, they’re now growing 25 per cent smaller than they used to. They’re also laying a lot fewer eggs, because egg production is linked to size.
To add to their challenges, lake waters are warming. In a research paper presented last year to an American Fisheries Society symposium, Casselman charted the rise in water temperatures over 60 years in the Bay of Quinte. The trend for the past ten years points alarmingly upward, with a Dec. 2001 temperature about 4° Celsius above the 60-year mean.
This is bad news for trout because warmer water shrinks their space and increases the space for bass. So bass multiply and eat more of the prey favoured by trout, as well as more of the declining number of trout fingerlings that hatch in the spring.
It’s a wickedly downward spiral for lake trout. Nevertheless, Casselman thinks they can survive as a species, although perhaps only in more northern lakes. And until he can find a way to reduce the pressure from bass, fishing may have to be restricted. But finding a way to curtail bass means raising hard-to-find funds for research.
What Casselman can’t change is the continuing increase in temperatures. He noted in his paper that when water temperature at spawning time increases by 2° C, the number of fry successfully hatched drops by about 60 per cent. When it increases by 3° C, the number drops by a whopping 95 per cent.
Meanwhile last week, after years of dithering, Ottawa finally tabled serious proposals for implementing its commitment to cut global warming gases. All I can say is, it’s about time.