Friday, March 4, 2016

How is climate change affecting the North's fish?

Trout Bay in early evening, smoked-in from a fire in the Northwest Territories, 1,000 miles away. Increased numbers of forest fires all over the North could be one reason the lake isn't getting much warmer since the smoke dims the sun's rays.
The farther north you go, the greater the effects of climate change. There's not so much if you live in southern Ohio, more if you live in northern Wisconsin and much more if you live here in Northern Ontario.
In particular the winters, with the occasional exception, start later, end sooner and aren't as cold as they were in the past.
Earlier ice-outs and later freeze-ups are probably having the biggest impact on northern fish populations, both good and bad. Until the milder winters get so warm there is no ice at all, they probably aren't changing the fish much. With the exception of stream species, like speckled or brook trout, I don't think it matters to fish if the lake ice is one foot thick or three feet. What matters is the lakes are frozen and they still are.
Earlier ice-outs could be responsible for the explosion of walleye in places like Red Lake. The sooner the lake is free of ice the sooner the fish can spawn. They then have a jump on the growing season -- the summer -- and should grow bigger and be in better shape when winter finally arrives.
Once the water cools off in the fall, the walleye go to deeper water and I don't think the late freeze-ups have much effect since the fish have been in their winter locations since mid-September anyway.
Late freeze-ups, however, do have a detrimental effect on fall-spawning species like lake trout. Lake trout are looking for 12 C water around the first week of October for spawning. If it is too warm, they don't spawn but rather re-absorb their eggs. We've seen this happen quite a few times in the 10+years the Ministry of Natural Resources and Forestry has been conducting their lake trout project at Bow Narrows.
If the water doesn't cool off to 12 C within a few days of  Oct. 6, the females give up and leave.
Red Lake's trout have a problem in successfully regenerating and this could be one of the reasons.
Another possibility is there might be is a naturally-occurring element that is inert at cold temperatures but is reactive at warmer ones. Lake trout eggs are about the most-sensitive things on the planet. The fish are hardy but not the eggs. So eggs spawned on rocks containing some element such as manganese could develop normally if the water temperature was, say 10 C, but croak if it is 11 C or warmer.
Researchers at the Experimental Lakes Area, near Kenora, reported this fall that climate change was harming lake trout populations there simply by warming up the lakes in the summers. The trouts' preferred temperature range just above the thermocline is getting narrower and narrower.
Only part of the increased lake temperature came from warmer summers; in fact, those summer highs haven't changed much. What has raised the water temperatures more was the runoff following the extreme rain events that are occurring everywhere. Those gullywashers send sediment into the lake, darkening it, and the sun then warms the darker-coloured water. Earlier ice-outs and late freeze-ups also played a role in water temperature.
The lakes they were studying were small and especially vulnerable to such an effect. I don't think Red Lake's average water temperatures have changed much at all. It has lots of very deep bays where only the surface ever gets warm. Our daytime highs have pretty much stayed normal over the years although part of that reason could be that the sun is sometimes dimmed by smoke from forest fires. Most of these fires are far, far away, like 1,000 miles or more, in places like Alberta, Saskatchewan and the Northwest Territories. Those places are having an increase in numbers of fires due to climate change. In Northwestern Ontario the summers haven't been drier than normal and therefore the number of local fires, almost all of which are started by lightning, has stayed relatively normal. The exception could be the Far North of Ontario, nearer Hudson Bay. There seem to be more fires than ever up there but that smoke goes east, not south.
It's hard for me to figure how northern pike are being affected by climate change. About six or seven years ago we had a record-early ice-out in mid-April and Brenda and I and Ben, our outside worker, went into camp soon after. Ben and I checked places like Douglas Creek to see if the walleye were spawning and it appeared they had, in fact, already finished. That would have been several weeks earlier than normal.
Northern pike, however, didn't even start to spawn until the first week of May and then continued to nearly May 20, just like they always do.
So, if there is a benefit to spawning early, the pike weren't taking advantage of it while the walleyes were.
More walleye in the lake, however, is a bonanza for pike since they provide a large school prey. If you're a 45-inch pike you get tired of fooling around with six-inch perch. Foot-long walleyes are pretty much what you are looking for.
The population of really big pike seems to be increasing every year and the walleye bonanza could be partly the reason. Conservation techniques such as releasing big pike by anglers are also responsible, no doubt.
My observation is there are far more walleye in Red Lake than in the past, about the same number of pike but more big ones, and fewer lake trout. So what I described above could be the reason or partly the reason for what I'm seeing.

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