Fish are shrinking

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It does.

Fish in the BWCA are definitely shrinking (or, more accurately, average size is decreasing and/or size distribution has changed w/ fewer big fish). Still enough big ones out there to make it fun, exciting, and challenging, but average overall size (especially of pike and lake trout) has decreased a lot. Walleyes, too, especially on the easily accessed lakes near entry points.

Probably an unavoidable element of (relatively) easy access wilderness fishing, but there are still lots of big ones out there, especially a few portages in.

On the plus size, the smallmouth and largemouth seem to be doing very well indeed. I've been especially (pleasantly) surprised by the number of tanker largies I've seen in recent years.

Most fish in the BWCA grow very slow in the infertile water and yes lake trout especially just inside the BWCA have gotten much smaller, and walleye in like the Kawishiwi river are extremely over fished. I wish because it is a wilderness area smaller limits and special regs to maintain quality but still allow a fish diner.
Smallmouth species have spread throughout the BWCA these last two decades and usually most are catch and release.
Black Crappie numbers in Basswood have exploded in size and number this last 10 years. Comparable to anywhere in the state. A real sleeper and unknown to most people up there.

There is a common misconception, typically with anglers who fish near populated areas, and where waters are naturally or artificially more fertile, that the BWCAW is all pristine, lightly fished lakes and streams.
Some native trout lakes only produce a half pound of fish per acre per year, so even light angler harvest can impact the fishery.

Think about lakes like Polly, Ensign, Brule, and Disappontment that have most of their campsites occupied all summer, and a steady harvest of fish almost daily. It adds up. Even big lakes like Basswood are probably impacted by harvest---at least in terms of size structure.

Obviously, every lake is different, and some lakes can sustain relatively heavy harvest (especially for smallmouth bass), but fishing pressure is definitely impacting the area's fish size and numbers---and this is reflected by the fact that fisheries are healthier, and fishing generally better, in Quetico than in the BWCAW.

A century ago, they would have been nearly identical.

I agree with Pinetree that the BWCAW should have a different set of regulations aimed at maintaining more natural distribution of fish sizes and excellent opportunities for large fish.

I wish bass were never introduced to these waters. I much prefer the native species.

I have not read that article. But as to fishing getting smaller from overfishing, my understanding is that wildlife management like MN DNR puts limits on the number and size of fish harvests and regulate depending on how healthy the population is. If there is overharvesting, they will drop the creel limit and institute slot limits. If there are too many fish in a lake, fish can get smaller due to less food to go around. If the bass size is getting larger and walleye’s are getting smaller, maybe they should increase bag limits on bass. I have no problems eating smallmouth, my friends and I find them delicious. We specifically target smallies and have a fish fry twice a week when we’re up there. A walleye thrown in is a treat, but my friends swear they can’t tell the difference. Wish we could take more home, especially if they’re stunting walleye population. But pike eat smallies, so they shouldn’t be affected by smallie numbers; indeed, if smallies are more abundant, pike should be getting larger since they eat them too. So, what’s the reason fish are shrinking in the BWCA? Is it truly overfishing? Then DNR should do something about it, change the regulations. I was just in Basswood 2 years ago and caught the largest numbers and sizes of smallies in the 8 times I’ve been there. Almost all catch and release except two 15 inchers per person to eat that night. Threw all egg laden females back. Are you saying they’re shrinking in all lakes in the BW or just the ones that are more easily accessed?

Pinetree: I wish because it is a wilderness area smaller limits and special regs to maintain quality but still allow a fish diner.

Do that many people bring fish home from their trip? I just dont know how cutting daily limits would impact it that much? I could keep 6 walleyes a day but I cant eat 6 walleyes a day.

Here is the article if you cant view it.

There’s something fishy going on in the water. Across Earth’s oceans, fish are shrinking — and no one can agree why.

It’s happening with salmon near the Arctic Circle and skate in the Atlantic. Nearly three-fourths of marine fish populations sampled worldwide have seen their average body size dwindle between 1960 and 2020, according to a recent analysis.

Overfishing and human-caused climate change are decreasing the size of adult fish, threatening the food supply of more than 3 billion people who rely on seafood as a significant source of protein.

As fish get smaller, there is less meat to cook per catch. So scientists are working to piece together why exactly fish respond to rising ocean temperatures by getting smaller.

“This is a pretty fundamental question,” said Lisa Komoroske, a conservation biologist at the University of Massachusetts at Amherst. “But we still don’t understand why.”


“How is it that we’ve known about this for so long but we don’t understand mechanisms?” she added.

The incredible shrinking fish
One undisputed reason so much marine life is getting smaller is fishing. Recreational anglers and commercial fishers alike like to catch large fish. That quest for the big ones leaves the small fries behind.

Rick Stuart-Smith, a marine biologist at the University of Tasmania in Australia, has surveyed coral reefs around the world. He said he can tell if a protected area has suffered from illegal fishing by the small size and sometimes even the shyness of the fish he sees while diving.

In truly protected areas “you’ll even see big fish in less than ideal habitats,” he said.



But there are plenty of marine species that face little fishing pressure that are still shrinking. To investigate why, Komoroske and her colleague, Joshua Lonthair, decided to grow their own fish.


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The pair started their experiment on sardines in California until the pandemic closed the lab in 2020. “We get a call that the facility is shutting down at midnight,” Lonthair said. “I’m in the lab actually taking my final measurements on those fish for our first set of measurements.”

The pair restarted their work in Massachusetts with about 400 brook trout reared for up to eight months in tanks. The scientists kept some of the fish in waters set at 59 degrees Fahrenheit while others at 68 degrees Fahrenheit. All were fed the same diet.

By the end of the experiment, the difference was stark. The trout raised in warmer waters were on average less than half the size as the other fish.

“You look at the fish, it’s so obvious,” Komoroske said. “Not that you don’t need statistics, but they’re clearly different sizes.” In the ocean, the phenomenon is so widespread it has a name: the temperature-size rule.

Putting theory to the test
For years, the leading theory for why fish grow to smaller adult sizes in warmer waters had to do with their gills.


Fish, unlike humans, cannot regulate their body temperature well. So when the water temperature goes up, so too does the oxygen they require. But, some scientists thought, the limited surface area of fish gills couldn’t keep up with the extra demand of a bigger body, leading fish to cut their growth short.

“That is the crucial point,” said Daniel Pauly, a marine biologist at the University of British Columbia who developed what today is called gill oxygen limitation theory. “Gills don’t go as fast as volume.” Climate change wasn’t on his mind at all when he began developing the theory in the 1970s when studying tiny tropical fish.

But more recently, when Komoroske and Lonthair dissected the brook trout, they found the gills of the fish raised in warm water were more than large enough to meet the animals’ energy needs, according to a study published earlier this year. In the case of the brook trout, the leading theory for why fish were shrinking appeared to be wrong.


A wild brook trout. (iStock)
“It doesn’t matter which species we do it on,” Lonthair said. “If it’s a global theory that the gills are going to limit growth, it shouldn’t matter if it’s a brook trout or a sardine or any other species.”


But Pauly said there is a different way of interpreting the data on the metabolic rate that shows gills do limit growth, and that other studies of the gills of other fish support his theory, too. He added that other scientists attempting to refute his long-standing theory are trying to “harpoon a big whale.”

Komoroske said her team is not trying to “pick fights” with their research. “This is how science is supposed to work,” she said.

‘It’s a problem’
Figuring out exactly why fish shrink in warmer waters is key for helping managers prevent overfishing in the warming open ocean and for helping aquaculturists choose the right fish to farm.

“We’re blinded to fixing problems if we don’t understand what’s causing them in the first place,” said Timothy Clark, a professor at Deakin University in Australia who has conducted similar experiments on fish and temperature.

Other explanations are that fish have evolved to stay small to survive hot spells, or that some other body system besides gills is limiting oxygen uptake and growth.


Salmon at Katmai National Park in Alaska. (iStock)
Whatever the reason, the shrinking-fish phenomenon could refashion ecosystems. “In marine and other aquatic ecosystems, size determines whether you are a prey or predator,” said Asta Audzijonyte at the University of Tasmania, who also studies fish size.


Smaller fish can produce fewer eggs, potentially altering ecosystems as ocean temperatures rise. For those who depend on the sea for their livelihoods, all those smaller fillets fetch a lower price.

“It’s a problem for the fishery,” said Art Bloom, a salmon fisherman in Alaska’s Bristol Bay with more than three decades of experience. “They don’t present as well in the supermarket.” During his career, he has had to switch from using nets with 5¼ inch openings to ones with 4¾ inch openings as the salmon he caught got smaller.

But there are signs of ecosystem health. Inês Martins, an ecologist at the University of York in England who found that nearly three-fourths of marine fish were dwindling in size, said many of those same species are increasing in abundance even as average body sizes goes down.

“There’s always a few winners and losers,” she said.

This article is part of Animalia, a column exploring the strange and fascinating world of animals and the ways in which we appreciate, imperil and depend on them.

Do that many people bring fish home from their trip? I just dont know how cutting daily limits would impact it that much? I could keep 6 walleyes a day but I cant eat 6 walleyes a day. "

You can’t keep 6 walleyes a day, you can only have 6 in your possession at any time. 4 in the freezer and 2 in your possession or any combination of those numbers. Creel limit of 6.

basswoodlakefan: "Do that many people bring fish home from their trip? I just don't know how cutting daily limits would impact it that much? I could keep 6 walleyes a day but I can't eat 6 walleyes a day. "

You can’t keep 6 walleyes a day, you can only have 6 in your possession at any time. 4 in the freezer and 2 in your possession or any combination of those numbers. Creel limit of 6. "

I understand the difference between daily and possession. You could keep 6 walleyes a day if you ate them that day. Which is why I brought up a daily limit. How many people are eating 6 walleyes a day? Or save fillets for the next day?

cwallace: "

basswoodlakefan: "Do that many people bring fish home from their trip? I just don't know how cutting daily limits would impact it that much? I could keep 6 walleyes a day but I can't eat 6 walleyes a day. "

You can’t keep 6 walleyes a day, you can only have 6 in your possession at any time. 4 in the freezer and 2 in your possession or any combination of those numbers. Creel limit of 6. "

I understand the difference between daily and possession. You could keep 6 walleyes a day if you ate them that day. Which is why I brought up a daily limit. How many people are eating 6 walleyes a day? Or save fillets for the next day?"


Maybe the MN DNR has that info

The article references the brook trout study - the warmer group, was right at the upper limit of where they die. Makes sense they were smaller. The fish were stressed, at temps that are near death for them. It would be interesting to see if there's a statistically significant difference if they only increased the temp by 2 degrees.

I mean - at that point why not increase the temp to boiling - look they didn't grow at all. The fact that they brough it to near the upper limit for where brook trout can survive, kind of negates the study for me. I think they needed five groups, one near the lower limit, so just above freezing, one at ideal, a group 2 degrees below, a group 2 degrees above and the group near the upper limit. So in the case of the salmon fishery they reference, is it it a few degree warmer temp or over-fishing? Is there an area, where the temp was previously near thier lower limit of prefered water temp and is now thriving?

I would also be interested to see how a few degree increase in temps affects warmer water species? I mean LMB grow alot larger in southern states.

One other thought - nearly all state record fish continue to be broken. Larger and larger fish continue to be caught. There's a few older records out there, but mostly they're being broken.

Speckled:

One other thought - nearly all state record fish continue to be broken. Larger and larger fish continue to be caught. There's a few older records out there, but mostly they're being broken."

This might be due to habitat restoration (like with lake sturgeon), strict size and kill limits (muskies), and changed ecosystems (like how zebra mussels and warmer temperatures have damaged a once-fantastic walleye fishery on Mille Lacs Lake, while benefitting muskies and smallmouth bass).

basswoodlakefan: "Do that many people bring fish home from their trip? I just dont know how cutting daily limits would impact it that much? I could keep 6 walleyes a day but I cant eat 6 walleyes a day. "

True. But three anglers taking two fish each has the same impact as one angler taking his 6 fish limit. The fact remains that a LOT of anglers fish the BWCAW when compared to how infertile the lakes are. And most foks probably are far more effective than they were a generation ago, as electronics make those mid-lake reefs and suspended fish visible.

The introduction and spread of smallmouth bass have definitely impacted the food chain on many lakes, impacting both walleyes an lake trout the most. Walleyes introduced into lake trout waters in the eastern BWCAW where they were not native likely degraded or eliminated lakers from some lakes.

I'd like to see a year-round, no limit fishing season for smallmouth bass in the BWCAW and a mandatory catch and kill for them on those lakes where lake trout and smallmouth are the only gamefish. The mandatory kill rule is often applied to invasive brook trout on cutthroat trout waters out west, so it's not a draconian thing.

arctic: "

basswoodlakefan: "Do that many people bring fish home from their trip? I just dont know how cutting daily limits would impact it that much? I could keep 6 walleyes a day but I cant eat 6 walleyes a day. "

True. But three anglers taking two fish each has the same impact as one angler taking his 6 fish limit.

So, if we cut the limit to two walleyes per person, does that change anything with 3 guys taking 6 vs 1 guy taking 2? Lol. I am not sure what's a reasonable number of fish for someone to have for a shore lunch. Or size for that matter. I can't remember the year but essentially, the DNR said dropping the limit to 4 would have no impact on the fisheries as a whole, if they (anglers) wanted real change it would have to go to 2 and nobody wanted that.

Also, it was brought up again at the roundtable a few months ago about going to a statewide 4 fish daily limit, with 8 in possession. Don't be surprised to see this on the floor in 2025-2026. Recent survey is basically split 30/30/30 for those in favor, those in not and those who don't care.

arctic: "

Speckled:


One other thought - nearly all state record fish continue to be broken. Larger and larger fish continue to be caught. There's a few older records out there, but mostly they're being broken."

This might be due to habitat restoration (like with lake sturgeon), strict size and kill limits (muskies), and changed ecosystems (like how zebra mussels and warmer temperatures have damaged a once-fantastic walleye fishery on Mille Lacs Lake, while benefitting muskies and smallmouth bass).


"

When was the last time you fished Mille Lacs?

Global warming is affecting lakes and like cisco and burbot in MILLE LACS. But the lake still has a very good-excellent population of walleye. Current regs are present because of biopolitics between the tribes and Mn DNR Fisheries. Most all of the present MN DNR Fisheries retired and still working will tell you the lake could easily have a 4 fish limit. Some have and given different duties or fired or reprimanded. Science takes a back seat on the lake. They do have so much good data on the lake, but not used objected by the tribe.

That said most lakes in Minnesota are overfished.

Yes smallmouth have ruined many stream trout lakes, the State abandoned stocking them. How they got into these lakes?

arctic:

True. But three anglers taking two fish each has the same impact as one angler taking his 6 fish limit. The fact remains that a LOT of anglers fish the BWCAW when compared to how infertile the lakes are. And most foks probably are far more effective than they were a generation ago, as electronics make those mid-lake reefs and suspended fish visible.

"

This to me is huge - maybe not in the BWCA so much, but definitely in our local lakes. The technology has tipped the scales to the point of being unfair and ethically questionable. With side imaging features it is so much easier to find fish these days

People argue, "well you still have to get them to bite" but the constant pressure definitely takes its toll. I have seen videos of people just cruising around looking for the trophy fish. Easy to see how fish populations and sizes can get nailed so easily now.

Wish the DNR would regulate electronics to put the sport back into it.

Pinetree: "Global warming is affecting lakes and like cisco and burbot in MILLE LACS. But the lake still has a very good-excellent population of walleye. Current regs are present because of biopolitics between the tribes and Mn DNR Fisheries. Most all of the present MN DNR Fisheries retired and still working will tell you the lake could easily have a 4 fish limit. Some have and given different duties or fired or reprimanded. Science takes a back seat on the lake. They do have so much good data on the lake, but not used objected by the tribe.


That said most lakes in Minnesota are overfished.


Yes smallmouth have ruined many stream trout lakes, the State abandoned stocking them. How they got into these lakes?"

SPOT ON.

RatherbeDuffing: "


Wish the DNR would regulate electronics to put the sport back into it. "

Where do you draw the line? People have been arguing about electronics since they came out?

cwallace: "

RatherbeDuffing: "



Wish the DNR would regulate electronics to put the sport back into it. "

Where do you draw the line? People have been arguing about electronics since they came out?


"

I don’t know, but I don’t have much hope that there will be regulation with the amount of money on the line for retailers.

Argo: "I wish bass were never introduced to these waters. I much prefer the native species."

Walleyes aren’t native to most of the BWCA either.

GunflintTrailAngler: "

Argo: "I wish bass were never introduced to these waters. I much prefer the native species."

Walleyes aren’t native to most of the BWCA either."

Good point.
I talked with the head of Quetico a few years ago.
He said water temps have really affected lake trout populations on marginal lake trout lakes.

RatherbeDuffing: "

arctic:


True. But three anglers taking two fish each has the same impact as one angler taking his 6 fish limit. The fact remains that a LOT of anglers fish the BWCAW when compared to how infertile the lakes are. And most foks probably are far more effective than they were a generation ago, as electronics make those mid-lake reefs and suspended fish visible.


"

This to me is huge - maybe not in the BWCA so much, but definitely in our local lakes. The technology has tipped the scales to the point of being unfair and ethically questionable. With side imaging features it is so much easier to find fish these days


People argue, "well you still have to get them to bite" but the constant pressure definitely takes its toll. I have seen videos of people just cruising around looking for the trophy fish. Easy to see how fish populations and sizes can get nailed so easily now.


Wish the DNR would regulate electronics to put the sport back into it. "

They tried once to regulate electronics in the 1970's, there is so much pressure by manufactures and certain groups of fishermen, the DNR never could pull it off. Maybe special regs for electronics in the BWCA would fly. Legislature and Govenor would have to push it thru.

Yes side view radar-locators will destroy fish populations in many lakes. Many who have them don't even fish until they run all over a lake and locate their quarry. They are so sophisticated.

Al Linder IN Fishermen use to say its all about Location-Location-Location when fishing. That is most of the battle in catching fish.

timf1981: "

GunflintTrailAngler: "

Argo: "I wish bass were never introduced to these waters. I much prefer the native species."

Walleyes aren’t native to most of the BWCA either."

Good point.
I talked with the head of Quetico a few years ago.
He said water temps have really affected lake trout populations on marginal lake trout lakes."

Yes many of the smaller shallower lake trout lakes will be hit hardest. Also as lakes warm, fish like smallmouth bass will survive better and compete for forage and eat lake trout.

Any chance plastics could reduce average size of saltwater fish? Guessing it wouldn't be a factor in freshwater and BWCA fish. But there seems to be plenty of plastic in the ocean, meaning saltwater fish would consume at least some plastic regularly, right? Plastic consumption in humans in recent years has been proven to reduce average size in reproductive organs and (if memory serves me correctly) overall growth.

I don't think growth rate has slowed in fish in the BWCA,except in cases where maybe smallmouth are consuming food that maybe walleye or lake trout ate.
Biggest problem is overfishing.
I have an old report of Creel census on Mountain and West Pike Lake dating back into the 1950's. West Pike Lake trout fishing was awesome. BUT THE DECLINE BEGAN, resorts back then motored across Clearwater Lake and stored boats od West Pike, the amount of lake trout taken was unbelievable in an untapped resource at that time. A 20-inch lake trout is 10-20 years old. Very slow growing. Well, West Pike size and number is smaller now.
Clearwater Lake in the 1950's-60's I had a photo of an individual in one day in the winter who caught and kept 3 trout 16- 20 ponds. These real big fish are like 30 years old, you can't replace them.

I will say tho Knife Lake, the lake trout fishing is better now than in was 55 years ago. Why?
The winter fishing by snowmobile in the 1960-70 era with 100's of people decimated the lake trout population there. Since snowmobiles were banned, the fishery has improved greatly.
The potential is still there if managed right and fisher people do their job on how and what they keep. Yes, eat a few more northern pike or smallmouth instead of trout.

Your whole post is spot on, Pinetree.

My friend and college roommate is from the Range, and his step-dad, and many others, would snowmobile into Knife in the morning, catch a limit of trout, ride home, and return in the afternoon for another limit. It was like saying f**k you to the DNR and forest service. Weekends saw a LOT of anglers on the lake, and the pressure really damaged the resource. But after snowmobiles were banned the fishery really recovered over the next 10-20 years, so Knife is back to being a productive trout lake.