Brook trout spawn is on in cold streams
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Chel Anderson is a botanist and plant ecologist for the Minnesota Department of Natural Resources. She lives here in Cook County and joins us periodically to talk about phenology or what’s going on in the woods right now. Welcome, Chel.
Anderson: Hi, Jay.
Well, I understand brook trout are spawning. So, let’s talk about brookies and the spawn.
Anderson: Yeah, well those who have been taking advantage of fishing the streams and inland headwaters of streams here in Cook County over the summer are no longer doing that for brook trout, because the season is closed, and a key reason for that is because this is the time of year when brook trout are spawning, and we wouldn’t want to get in the way of the spawn, now would we?
No, no, because then you don’t get little brook trout.
Anderson: That’s right, because then your fishing the next year and years after would not be nearly so promising. So, yeah, brook trout are one of the two native trout species to Minnesota, the other of course being lake trout. Here in our part of the northeast, we have both a coaster lake trout which lives most of its life in Lake Superior, and we also have a stream brook trout that live in the headwaters and upper reaches of streams.
Do they get into lakes, too?
Anderson: Yeah. They are in lakes and ponds. I’m going to focus on the spawning of the brook trout that don’t spend any time in Lake Superior, because they’re really pretty different. But the brook trout that live in the headwaters of our streams here are cold-water loving species. So, this is where these fish are going to be focused on spending their time and doing their spawning. Brook trout, if one hasn’t ever seen one, is kind of a medium-sized fish, dark back, lighter sides and belly. The belly often has some red; the lower fins have some red on them. They have beautiful modeling on the dark part of their back and upper sides, and then they also have beautiful spots which are red and trimmed with blue. So this is, at least in my opinion, one of the most spectacular fish that one can ever see. They rival any fish I’ve ever seen on a coral reef and have this very close association with what are really rare environments even in Minnesota. Their close association with cold water environments make them a good indicator species for water quality in streams and rivers here in the north. At this time of year, the females are looking for places where the springs are actually coming up through a gravel, sandy, gravelly kind of substrate. They’re interested in finding those particular places for two reasons. One, because that water that’s coming up is cool, so it stays cool all the time and because that constant flow helps maintain the substrate there free of silt and it’s also a place where they can easily make what’s called a “redd” which their nest that they are going to put their eggs in. So, they’re looking for these spots and they’re swimming hard into the bottom and they’re vibrating their bodies and swishing their tails, and over the span of a few days they are doing that in that spot and creating this shallow nest or “redd.” During that time, there may be a male that is defending that against other males while the female is working on creating the redd. Once the redd is ready, the female is satisfied with it, then she’s going to kind of lie still in the redd, just kind of maintaining her position there, and the male will come over and might do a little bit of courting. Then, he’s just going to arch his body over hers and she’s going to release the eggs and he’s going to release the sperm at the same time and they’re going to be vigorously vibrating their bodies and churning the water, so there’s a lot of mixing that’s going to go on when that release is happening. Of course, that’s essential to make sure the eggs get fertilized. Then the eggs will settle down in that depression. The female, then, with swipes of her tail, will move some gravel from the edges of the redd out over the eggs and cover them with a light layer of gravel. So, now they’re kind of stuck there in that nice place where there’s this constant flow of oxygenated, cool water. They’re looking for water temperatures between 40 and 49 degrees, is when they really want to be working on their spawning activities. The eggs are going to develop there. Depending on how cold the water is, it may take anywhere from 50 to 150 days for the eggs to develop and hatch out as tiny fish. They’re going to spend that time right there in the redd, and maintaining that open, oxygenated condition of water moving through is essential to the survival of the egg. So, that’s where the linking of the high-quality conditions of the watershed are so important to the success of the spawning, and the success of the eggs.
And they’re developing under the ice?
Anderson: Yes, they’re developing under the ice. But, of course, because there’s a spring flow, those aren’t going to be places where the ice is going to form right stuck to the gravel, right? And so the fish are very careful about the spots that they choose. The importance of watershed quality is that we don’t want silt coming in and settling over these places. Of course, a small spring flow can only keep off a small amount of sediments coming through in the stream or in a pond. It’s an out-of-sight kind of activity that’s going on, but so important to something that people enjoy so much about coming and living here and visiting here fishing here. You know, I don’t know how many people I’ve talked to over the years who there’s no greater delight for them than spending a day touring through the woods trying to get to their favorite brook trout fishing area. I mean, these are such important aspects of many peoples’ time here, and it’s important to remember that it persists because of some things that go on outside of our easy-to-see or easy-to-hear kinds of experiences, but they’re really important none the less. Brook trout don’t die after they spawn, they live, you know, three to four, maybe up to six years and they spawn every year of their adult lives. They are usually ready to spawn at just a year old.
Yeah. That’s my next question. How fast does it take these little guys to grow?
Anderson: Yeah, they grow pretty fast, and usually within a year or so, they can be ready to spawn the very next one.
Chel Anderson, DNR botanist and plant ecologist. Thanks, Chel, for helping us understand brook trout this fall.
Anderson: You’re welcome.
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