Fish population impacted by historic heat

[00:00:00]Yeah, so Minnesota's recent heat wave isn't just taking a toll on people. It's actually resulting in a massive fish kill in area lakes as the DNR says that low oxygen and warm water is to blame. Dr. Isaiah Tola, he is the fish health supervisor at the Minnesota DNR and I'm telling that we need a couple more minutes to make sure that his audio is all right. But so let me just tell you what is happening here.

[00:00:27]Um with that prolonged heat wave that we experienced last couple weeks, hundreds of reports of fish kills were going on across dozens of Minnesota lakes.

[00:00:38]So the DNR says that superheated water, so that's water surface temperatures reaching into the upper 80s holds significantly less dissolved oxygen while simultaneously simultaneously fueling algae blooms that consume any of the remaining oxygen. As a result, as you can imagine, that results in a lot of fish dying and washing up on shore. So Dr. Isaiah Tola joins us now. Dr. Tola, very interesting. Tell us what's going on in these lakes after the heat wave.

[00:01:17]I'm not sure he can hear us.

[00:01:19]>> I can hear you. Can you hear me?

[00:01:21]>> great.

[00:01:22]>> Okay.

[00:01:22]>> Yes, so just let us know what is going on in these lakes right now with that extreme heat that we experienced over 10 days.

[00:01:30]>> Yeah, so generally what we see with fish mortality events across the state is that there's usually a pulse of events right after the winter conditions.

[00:01:42]Um and then we'll see another pulse of events in the summer.

[00:01:47]This summer we have kind of an interesting case where we're seeing a second more severe pulse of fish mortality events across the state.

[00:01:56]And we're not just seeing those in the waters that we expect to see them in.

[00:02:01]Generally, we see more events in the metro area in lakes that have more severely impaired water quality.

[00:02:10]But the current pulse is affecting more fish um in lakes that have higher water quality.

[00:02:17]And generally, we're seeing that the species that are affected are ones that are more sensitive to high thermal conditions.

[00:02:28]>> Why do you think that is? I mean, why are you seeing more now than you have before and in lakes with higher water quality?

[00:02:37]>> Well, as a lot of your viewers are probably aware, um water temperatures have been increasing um across the last 50 years in Minnesota.

[00:02:47]So, we've seen about a 4° temperature increase in Fahrenheit.

[00:02:52]3.78°.

[00:02:54]And we've lost about 14 days of ice cover in Minnesota.

[00:03:00]Um so, this summer is no exception to that rule. It's a really warm summer um with a uh kind of a record, you know, um heat wave that's going on right now.

[00:03:11]And because of that, we've seen an increase um 30% increase in mortality events uh um in the last week over a 4-day period.

[00:03:20]>> But it's not unusual to have a hot July.

[00:03:23]July is generally the hottest month on record, and we didn't set any records. I mean, we've seen longer stretches of 90° weather. So, so why now?

[00:03:33]>> Yeah, so generally, we do have, you know, that kind of one sort of peak of of high temperatures that's coincides with uh fish mortality events across the state. Right now, we're kind of seeing those like this double peak of high temperatures, and that's causing, you know, high water temperatures in rivers and lakes across the state.

[00:03:51]>> I would imagine that especially Minnesota fish are used to temperature fluctuations. I mean, they live in the lakes. Most of them unless they migrate through the streams and the rivers. Most of them live out the winter in the lakes when the lakes freeze and then they're here in the summer when the water is, you know, in the 80s. So, I imagine they're used to the water fluctuation. Is it just that algae bloom that's that's really impacting?

[00:04:19]>> No, I mean, there are more mortality events every year. So, you know, we're not seeing like a huge departure necessarily from mortality events across across the state. So, if you have waters that are more impacted for high nutrients, they have a lot of urban or agricultural runoff going into them.

[00:04:37]They're going to be more susceptible to mortality events. And the reason for that is is that those excess nutrients are going to be leading to algae blooms are going to be leading to other bacterial or plant decomposition in the lake and it's using up oxygen.

[00:04:53]So, we expect to see those, but what we don't necessarily see every year is like kind of a rapid pulse of mortality events happening over such a short period of time. And the fish that are being impacted, you know, the ones that we're talking about right now at this current pulse, it's mostly fish that are more thermally sensitive like northern pike, muskie, walleye, and then some just very large species of fish or large large fish of certain species like large sturgeon that are showing up in some of these mortality events.

[00:05:24]And that makes sense because certain fish, the larger they get, they're they're more sensitive to thermal impacts. Um basically their gill to to body surface ratio becomes less favorable as they get older and so they're more sensitive.

[00:05:37]>> Hmm, interesting. Are there certain type of waterway that's more susceptible to this? I mean, I'm imagining maybe shallow lakes, Uh what are you guys seeing?

[00:05:48]>> Yeah, so I mean shallow lakes for sure.

[00:05:50]Um uh also as I've mentioned before, lakes that have um nutrient impairments. So, if you go to Lakefinder and you look up your lake of interest, the one that you're interested in, especially if you're in the metro, and look at the water quality tab, you can see exactly what I'm talking about when it comes to um the uh water quality um and lake health um data. Um so, those lakes are going to be more susceptible. Um one really interesting one we just recently um visited is a lake that has relatively good water quality, like Peltier. Um and it has a a dam that feeds into um a shallow lake downstream, uh George Watch. Um and that dam is actually a structure that impedes movement of fish between the two lakes. It's just, you know, part of the the nature of living in um landscapes that are dictated by people that sometimes we build structures that um that get in the way of wildlife. So, in this case, we saw a lot of large um really nice large northern pike that um were trying to leave uh George Watch Lake and they were moving towards the dam that has kind of this waterfall. Um better dissolved oxygen conditions, better water temperature right there. And so, a lot of those fish all piled up in a place where they're really visible uh to the public and then they died there and weren't able to reach any cooler water.

[00:07:04]>> Interesting. Uh is this going to change anything for anglers across the state or should they change their habits because of this happening?

[00:07:13]>> I mean, it's hard to say. I would say that a lot of really dedicated anglers um who are targeting some of these more sensitive uh species, um you know, people who are going after trophy size muskie or sturgeon um are well aware of the risks of fishing during excessively warm temperatures. First off, you're just not going to have as good of a fishing trip in some cases. And um at other times, you know, if you're catching that trophy muskie and the water temperatures are well above its stressful condition, um when you release it, you may have a little heartbreak and you may see that fish roll over and float up to the surface and die and no one wants that. Um, just for general anglers though, I would say, you know, go out and still enjoy fishing, but maybe consider um, harvesting your limit and then um, ending your fishing trip there or um, consider um, uh, you know, when you're catching fish and you want to release them, just leave them in the water before you release them or if you're going to take a picture, just take them out for just as short as you possibly can and put them back in the water so that they can um, recover.

[00:08:15]Um, so that's just kind of some general recommendations. I'll also say too that if you're um, fishing in a lake that has an active fish kill, just be very careful. Um, you know, any lake that has a bunch of decomposing animals in it is going to have increased bacterial loads.

[00:08:29]There could be harmful algal blooms there that um, have some health concerns. So, you know, contact Department of Health if you have questions, but um, you know, be real careful um, fishing in lakes that you see thousands of dead fish on. Um, I think that maybe goes without saying, but you'd be surprised.

[00:08:45]>> Well, and I was going to ask you about recreational use. You know, swimmers, um, boaters.

[00:08:50]Is there anything that they should be paying attention to? Obviously, if you see a bunch of dead fish in the water, don't swim.

[00:08:59]Um, but maybe it's not as visible, you know, if you're out in the middle of the lake. What do you want those recreational users to know?

[00:09:06]>> I mean, definitely check out um, uh, Pollution Control Agency and Department of Health have some really good websites that specifically address harmful algal blooms. Um, there are a number of websites that will actually tell you what like the micro system levels are at beaches, um, popular beaches around the metro area. So, check those resources and make sure that the water is safe to swim in. Um, I'm a fish guy at DNR, so I'm not really going to speak to public health too much. Um, but it's something that people should be aware that those resources exist and they can check them and see what the the safety is um, when you're thinking about planning that swimming trip or waiting trip. So, >> And what about the dead fish? I mean, when you're seeing a a bunch of fish wash up on shore, is the DNR just leaving them there or is there another use for those fish? I'm thinking like fertilizer or I don't know, like donating them for feed or something.

[00:10:00]>> Yeah, I mean, this question comes up a lot and I think like, you know, the you know, first off, DNR doesn't go and clean up dead fish. I mean, there's just sort of some issues with our ability to to get staff out to that. We have a lot of other work that we're doing and going out and cleaning up fish is probably not something that the public really wants us to do.

[00:10:20]It's it's not necessarily a super feasible task.

[00:10:24]Now, I will say that another issue with you know, kind of leaning on natural resource staff to go and do fish cleanups is that you know, a lot of these fish are dying because of the the like these chronic issues with nutrient impairments and other water quality issues in lakes.

[00:10:40]And so, you know, kind of eating up more of our natural resource management staff time to go and clean up fish is probably not going to be in the best interest of trying to work towards improvement of water quality in those areas, which is you know, maintaining habitat, maintaining healthy populations of fisheries is really what we're focused on. Cleaning up the mess after a population is impacted by poor water quality and then dies is probably a poor use of time.

[00:11:09]>> Okay, we're back in average temperatures now, but what if that extreme heat returns?

[00:11:18]>> Yeah, so if that extreme heat returns, I think that we're going to be in for more of these reports. It's you know, like I've said before, you know, we're kind of at a at a level right now where we're having still a a relatively normal year except for this current pulse of like a lot of events all at the same time. So, we would expect to see more mortality events across the state. Um probably um what we'll see too is that right now we're just looking at events that for the most part are um involving sensitive species, but we'll start to see some of those more resistant species start to die off. Some more cases that involve primarily carp or panfish, um bass, um these more what we call like warm water species we might start to see those uh show up in these mortality events if conditions don't improve.

[00:12:04]>> Okay, so interesting. Dr. Isaiah Tolo, the fish health supervisor with the Minnesota DNR, I so appreciate you joining us.

[00:12:11]>> Yeah, thank you for your time.

[00:12:12]>> All right.