There are few more beautiful and accessible walks in 麻豆社国产than those beside the 麻豆社国产Valley Golf Club, next to the dynamic Mamquam River.
If you have walked these trails over the last couple of months, since about mid-August, you likely noticed how dry the fish-bearing channels are.
This isn't a new phenomenon, it increasingly happens in the late summer.
The 麻豆社国产Streamkeepers rescue coho fry from the channels when the water levels drop and the 麻豆社国产River Watershed Society actively studies the channels and is working with the golf course on long-term solutions.
The 麻豆社国产 caught up with Murray Manson, the section head of Fisheries and Oceans Canada (DFO) Habitat Restoration Centre of Expertise, to get some background and insight on the channels.
What follows is an edited version of that conversation.
Q: First, as a bit of background fact-checking, the area around the golf course used to be the riverbed of the Mamquam, right?
A: Well, it's all part of the floodplain of the Mamquam River. It's now combined between a dike on both sides. So, it used to be free to sort of move around over hundreds of years, and now it's sort of stuck between the two dikes.
Q: And the channels beside the river, next to the golf course, were constructed by the DFO, correct?
A: Yes. I think the first one went in, in the 80s. At the time, we had dug a number of these groundwater channels at different locations, sort of throughout B.C. They would go onto the floodplain, and often in areas where there's a dike, if you dig down, you could reach the point where you encounter the groundwater surface, and then if you dig a channel out, there's usually beautiful gravels right there, and the water just begins flowing down, and you create an outlet back to the main stem of the river. And they're very popular with chum salmon and coho use them really a lot too. They built a bunch of them at the time, and they've been really successful over the years.
Q: I saw coho using the channels; what else uses the channel?
A: Chum salmon would have been the main focus, then right from the getgo, coho moved in.
It was an interesting sort of dynamic between the coho, because they spent a year in the freshwater, and then the yearling will eat the emerging fry from the chum. So there's a lot going on in those tunnels.
The coho, it comes out of the gravel in the spring, and it's going to stay there for a full summer and over that next winter, and then it'll be there in the spring the next year, when the chum that came in that fall come out of the gravel. So, the coho will be, say, eight centimetres long, and chum will be three and a half centimetres long, and so the coho will eat them.
Q: What about steelhead? Do they not use the channels?
A: Juvenile steelhead, that's not the kind of habitat that they are typically going to go in and spawn in. They are going to be in the main stem. But, you would see both cutthroat and steelhead trout poking in there, probably in the juvenile phases, though, for the most part. Cutthroats are predators, and they might come in and eat some of the fry at certain times a year. And we find a lot of sculpins and just the typical small freshwater aquatic species that are common in streams, too鈥攁nd amphibians, too.
Q: We can see refuse boxes鈥攚ooden boxes dug deep into the water of the channels. Can you tell me a bit more about them? They are put in by DFO, correct?
A: We just put in two. We try to get them as tall as possible, like about eight feet鈥攁 sheet of plywood high. You dig a hole in the stream bed, and then you lower this box down into your hole until just the upper bit of the box is out. When the water level comes up in the fall, that box will be full of water, and fish could swim in and out of that slot on the front of the box.
It's for the juveniles, and particularly coho, because, like I was saying, the coho are going to have to spend their first summer after coming out of the gravel in the channel. We've placed those boxes in areas where the juvenile coho, as the water is dropping, will be seeking out refuge areas, and we'll get in there. And then when the water does go subsurface in the channel, there's still four feet of water in the box because the box is so deep.
The hope is that they survive the dry period, and then when the flows come back up, they can swim out of the box and go about their merry way.
There's been two boxes in those channels for a while, and one of them has been really successful. The other one wasn't working so well, and so we took it out. There are three in there now, in total.
Q: Since these channels were originally put in, we're getting more dry periods or starting to see more dry summers with climate change. Does the DFO have a plan for the area? Or what are you thinking about what could work?
A: You heard about the [麻豆社国产River Watershed Society] groundwater study, and so we're just trying to get a sense of where the groundwater level at throughout the season. How does it change? How does it link the flows in the river, and maybe, what else is going on? And then, you know, then we can sort of start coming off with a coherent plan to how we should treat these channels.
If we just dig them deeper and then there continues to be trending in climate, then we may be just sort of chasing water down continually. And we don't really want to get into that. It's also really costly. If we were to drop all those channels by a metre, and you got to take the material somewhere. So, maybe what the solution is, is we dig some areas that sort of become ponds during the season, when the channels between the ponds go dry, maybe the fish can survive in ponds. But we'll have to find the right locations for those. So, we have to come up with a plan that everybody's happy with, and then we will try to implement it over the next couple of years.
Q: What depth and temperature of water do the fish need?
A: With regard to the depth, if it gets really shallow, they become very susceptible to predation. And so, if we were to design a pond for rearing, we would try to get it like at least a metre and a half deep, and we would have logs and things in there so that the fish could hide and seek cover from predation. For temperature, salmon are coldwater-loving species, and when temperatures start getting up sort of above 15 C, when they get to 18 to 20 C, then the fish start getting stressed. The other thing that happens with water as it warms up is that it holds less oxygen, so there's a double stressor there鈥攖hey start running out of oxygen to breathe because the oxygen level will drop.
It's a sort of a combined challenge for fish in the pond. Hopefully, in the middle of the summer, they'd still be at 15 C or less. The colder, the better there.
The dissolved oxygen just has to stay high enough so that the fish can continue to respire.
Q: During the heat dome in 2021, what did we see with the fish in those channels?
A: We certainly saw fish stranded. And then, you know, when the water drops away entirely, they just, they're just high, dry, and they expire, right? And we see a lot of that, actually, not only in the heat dome, but it's something that happens in the summer during the overflow periods across the landscape, right? Not just in the Mamquam.
When you start looking at the kinds of dry summer, low snow packs that we've been having in recent years with climate change, there are certain streams that may have been marginal for coho, and now they're becoming impossible for coho to survive the summer. We may see streams that were productive coho streams becoming much less so with the way things are going with the climate and streamflows.
Q: Anything else you'd like people to know about those channels in particular?
A: I would emphasize that we are still trying to understand exactly the dynamic between the river flows and the level of groundwater that we're seeing and the water usage as well. We don't have any 100% answers yet. But there's a lot of interest, and the golf course management has been helpful. They're working with the 麻豆社国产River Watershed Society and they are communicating well.
