Eastern Baltic cod grow much smaller than they did due to overfishing | Hacker News Reader

Eastern Baltic cod grow much smaller than they did due to overfishing

smithsonianmag.com

273 pointslittlexsparkee89 comments

My take away from this is that letting the small fish go under the premise that they are juveniles that will later grow to be bigger lets the adult midgets go, ruining the gene pool. I wonder if this finding will have any impact on conservation rules against taking small fish when fishing.

> ruining the gene pool

In what sense? Is being bigger Platonically better than being smaller?

It's better if you want to eat them lol

Small fish generally taste better in my experience. Small of course implies younger, so we let the biger ones go as well as small ones - there is a too small to eat point.

> Is being bigger Platonically better than being smaller?

Maybe, most animals evolve towards larger sizes. Except on smallish islands, where they tend to become smaller.

> Maybe, most animals evolve towards larger sizes.

This is not even a little bit true.

> Maybe, most animals evolve towards larger sizes.

Animals tend towards whatever size lets them maximise survival. This is based on available niches and other selective pressures.

> Except on smallish islands, where they tend to become smaller.

Island syndrome leads to both gigantism and dwarfism.

> Animals tend towards whatever size lets them maximise survival.

Evolution is a filter that removes unfit, it does not select the best fit. So a lot of mutations that slightly decreases fitness for the environment stay as they do not make an organism too unfit. This results in a gen pool diversity in a population that helps to survive if the environment changes as previously somewhat harmful mutations can be essential for survival in the new situation.

Presumably the optimal size for survival when humans aren't applying pressure via fishing is bigger. Perhaps "ruining" is hyperbolic, but this is making the fish less fit for their environment.

...less fit for their environment excluding human fishing pressure.

It is making them less fit for their environment? I can see how it is making them less fit for the environment they used to be in before they were subject to large scale human fishing, but that's not their environment now.

If that’s the case it should return if we stopped fishing.

Not always the case. Any number of things can happen that could prevent that from happening, like extinction, as an extreme example.

No. A certain gene expression can just be gone forever. Nothing guarantees the desired expression will evolve again.

Sure it does, there is still variation in the sizing of them. If the previous size was the ideal one, and assuming that has otherwise not changed, the larger cod will be more fit and breed more.

https://en.wikipedia.org/wiki/Hysteresis

Their environment is one where humans prey on them, especially on the large ones. It's a selection pressure like any other and becoming smaller on average makes them more fit for that environment.

if you're interested in maintenance of the fishery, size reduction is a primary indicator of failure. so yes

In the sense that the gene pool is being unintentionally manipulated by humans, when the original goal was to try and leave it undisturbed to an extent.

Yes. It is.

maybe, but how can you possibly tell - in bulk - if you are dealing with a midget or really a young fish that had no chance to spawn? (which is the point here)

trawlers historically haven't really discriminated by size. development of decent selective trawling equipment, and introduction of a minimum size is fairly recent

as a data point, a recent change in regulations regarding eastern Baltic cod had no statistical effect on reported catch https://link.springer.com/chapter/10.1007/978-3-030-03308-8_...

>Data quality for stock assessments has deteriorated, discarding of cod has not decreased despite a reduced minimum size and there are no indications of increased gear selectivity in the fishery

...haven't /INTENTIONALLY/ discriminated by size...

The article says smaller fish could more easily escape the nets. Though it doesn't cite studies documenting that, it does seem reasonable.

> My take away from this is that letting the small fish go under the premise that they are juveniles that will later grow to be bigger lets the adult midgets go, ruining the gene pool.

I read about this being tested in large fish tanks using either cod or trout some 20+ years ago, where they removed fish either randomly, or let the small ones go. They came to the same conclusion: letting small fish go results in reduction of average size of mature fish after a few generations.

The authors of the submitted paper references this[1] article, which points out the following:

Despite a theoretically strong conceptual basis, evidence of genetic change unequivocally attributable to wild-capture fisheries has been elusive. Among the top five threats to biodiversity, evidence for genetic trait change is strongest for studies of pollution and weakest for studies of overexploitation (and habitat change). Determining whether phenotypic change in declining populations is the result of evolution, as opposed to other influences on growth, survival, and fitness, or gene flow from adjacent populations, has proven challenging.

So this paper seems to provide evidence that the lab results holds up in the wild.

[1]: https://www.pnas.org/doi/full/10.1073/pnas.2105319118

Id think the small fish are let go more often because they aren't good eats. No one is trying to cheat the warden for a six incher.

A good chunk of fish caught are ground up and fed to chickens/other fish.

The grinder doesn't care what size the fish are.

Being small is an evolutionary advantage in this case so that is understandable outcome. On the other hand for maine lobsters they let large males and egg laying females go with the large life spans of lobsters would be hard to compare if they getting larger

There is a curious case with small male salmons: From https://www.fishingwithrod.com/articles/fish_biology/whats_u...

> Size obviously matters when it comes to mating for salmon. However, being a small male can also succeed when it comes to scoring a female. The so-called "jacks" that are found in chinook and coho salmon are male individuals that return to their natal streams a couple of years earlier than expected.

> Although they are much smaller than a fully grown male, they are also sexually matured when they reach the spawning ground. What advantages do these smaller fish have? It is obvious that they will not win when confronted by a fully grown male. Behavioural biologists believe that these jacks are "sneaker males". Their duty is to simply stand by when larger males are fighting for territory, and sneak in while unnoticed to mate with the females that are also waiting for the fights to end. As you can see, being big does not always have all the advantages, sometimes being small can be very beneficial too.

IIRC the female already laid the eggs, and the big males start to fight. During the fight the small one sneaks a fertilice them. "Waiting" and "Mate" are misleading.

It's kind of hilarious to me that the female watches the males fight to the point that she doesn't even watch her own eggs. I wonder how long these jacks have been around?

IANAB IIRC salmons lay the eggs is swallow holes in a quiet part of the river. She is problably thinking that those idiots are going to spill the eggs and they will be drafted by the water and die, so she has to try to keep the fight away.

Here is a decade old study talking about that: https://www.science.org/doi/10.1126/science.aac4249

As a former commercial fisherman this is something we talked about on how there should be a max size limit.

The other thing about the Baltic Sea is that there has been so much fertiliser and toxic farming chemicals running into it since the start of the agricultural revolution that the fish is full of heavy metals and toxins. The Swedish authorities recommend against eating it more than once a month and never for pregnant women and people with health conditions.

This farming runoff overload has also led to huge areas where the sea floor is completely dead.

Crabs in the Chesapeake Bay are the same. About 80% of tidal segments there are contaminated with PCB's and heavy metals. Regulators describe them as "impairments", and recommend not eating them more than once per month. Cod are bottom feeders and are affected by pollution that settles to the bottom.

Classic and, as usual, nobody is held accountable for it. Classic EU.

From what I recall this runoff was the most intense between 1950-1980.

I'm sure I read somewhere that Maori fishermen used to eat small-mid sized fish and left the largest ones because they were the best breeders. I can't find a reference now but has logic.

That is for eels.

I met a fella whose income came from going up coastal streams (canoe? Dingy with outboard?) to catch eels to sell. He definitely left the largest (queens?).

Good article: https://ourwayoflife.co.nz/from-vermin-to-icon-new-zealands-...

Also interesting: https://www.1news.co.nz/2025/04/05/thousands-of-eels-found-d...

In most fish, larger size = more eggs or more sperm. So yes, largest ones are typically the best breeders. IIRC some species like I think some tuna they don't harvest the largest on purpose.

Had to truncate the title to fit 80 char limit

Pertains to Eastern Baltic cod, not all

Eastern Baltic Cod Shrinking for Decades; Scientists Have Answer

Scientists Find why Eastern Baltic Cod Shrank for Decades

Or, still fitting:

Scientists Find Eastern Baltic Cod Shrank due to Overfishing Affecting Genepool

Eastern Baltic Cod Shrank due to artificial selection

Artificial Selection Shrunk Cods.

This is why I'm afraid of mosquitoes. Fighting them means creating a superhuman (super mosquito?) version that will be resistant to everything. When they find new diseases to obliterate the human race with, we are done.

Personally, I believe that mosquitos are far more concerning than any other impending environmental disaster.

Technology and memes spread faster than genes. Mosquitoes adapting that fast is not an issue that serious. Additionally, if hundreds of thousands of Americans died of malaria each year, we would have found much more effective cures (consider that there are already very effective ones that simply aren't widely used), just like we did with Covid.

The U.S. would quite simply not exist if it were a malaria zone. Endemic diseases shape societies, profoundly.

I don't like how this is worded. Makes it sound as though the cod are actively reducing their size. But this is very straight forward Darwin's Theory, survival of the fittest, in action. In this case, the "fittest" cod are the ones with the propensity to be small, since they can escape the nets and survive to breed and pass on that propensity.

And it follows that there won't be a "bounce back" of the larger cod any time soon, as it takes thousands of years in a minimally interrupted state for such diversity to come about in nature. Of course this applies to all other living creatures as well.

> it takes thousands of years in a minimally interrupted state for such diversity to come about in nature

The article says it only took 30 years to kill off all the big cod by only allowing the generically-smaller cod to escape and continue breeding. Now that all the eastern cod are protected, maybe it will only take 30 years for the gene pool to return to normal size distribution.

I'm pretty sure it doesn't work like that: previously there were genetic variants for large and small sizes. Now a high proportion of the larger variants have been removed from the gene pool. To reverse that in a similar time frame would need a massive selection pressure on the smaller variants. So you would need something like industrial scale fishing that removed the smaller adults, but didn't take out the juveniles who would become big fish, while also letting go the bigger adults. It doesn't sound feasible

Related, this is an excellent book on Cod fishing and how it helped humans and finally how overfishing has hurt the Cod numbers: https://www.markkurlansky.com/books/cod-a-biography-of-the-f...

It might sound like a boring topic, but it's one of the best books I've read and something I recommend a lot.

By the author of Salt and interesting in the same way for the same reason. Much shorter!

I've often made the argument that evolution can happen very quickly within a few generations and doesn't necessarily take millions of years. It's interesting to see some cases in nature where rapid changes in a predator's behavior (in this case humans) can radically alter a visible trait.

I knew someone who started a farm of Spirulina (a microscopic, edible algae [cyanobacteria]) in a very different climate from where the seed culture originated. They did really poorly for the first few days, they were the wrong color and the culture wasn't growing. But eventually they adapted to the new climate and bounced back, and he was able to scale the culture up to multiple greenhouses and harvest it on an ongoing basis.

Before concluding a genetic change took place I would want to rule out alternative hypotheses. Maybe the cyanobacteria needed to do a mode switch which took time, maybe some parasite had to die, or some symbiote had to enter the culture. Yeah I'm just kinda throwing things out there, but still.

The one that gets me is the Soviet experiment in domesticating foxes that worked after a few dozen generations. How many generations have humans been around with tools and technology? We've been domesticating ourselves.

Is this really an argument or just fact? From what I understand, the modern accepted view of evolution is that it happens in a sudden step wise manner... there will be an equilibrium, where the ecosystem is fairly stable and species don't change much, and then some shock or change will happen and evolution will be rapid, over a relatively short period.

This makes sense if you think deeply about it; evolution will only happen when the 'normal' genetic expression stops surviving, otherwise the random variations will even out.

I assumed most of the actual genetic variation comes in during times of plenty, when you can have lots of offspring without worrying about them being perfectly tuned for their environment. Then a shock comes along, straining the population in some way, and whoever happens to have the right genes simply survives. The "millions of years" thing is probably for becoming a whole separate species, no? Like our ancestors turning into homo sapiens.

point being: I imagine it's sorta the opposite - evolution happens when things are stable, but the species is only shaped towards it during hard times

edit: This is reflected in the mammalian explosion - while dinosaurs ruled the earth, things were stable. asteroid comes, hard times arrive, mammals suddenly explode because they were most-ready to take over new environments thanks to their already-developed genes. Millions of years of honing all that led to H. Sapiens, the hot new species

I think the genetic variation you get when times are plenty will only hover around the mean, though, until some restraint pushes it a specific direction.

Here is a simplistic example of what I am trying to say:

Imagine you have a population of creatures, and they have some gene (or combination of genes) that controls how much cold they can tolerate. Some can tolerate very cold weather, some can barely tolerate any cold weather, and some are in the middle. They all can live happily, and mate randomly, meaning the individuals who have a high cold tolerance will (on average, since most other individuals by definition will have lower cold tolerance) mate with an individual who has lower cold tolerance. In other words, the next generation will genetically regress to the mean.

This continues on as long as all the individuals can survive at basically the same rate.

Now, imagine there is suddenly a very cold winter, and the individuals who can't tolerate cold die off. Now, there aren't any (or many) individuals with low cold tolerance for the higher tolerance individuals to mate with, meaning it won't regress back to that mean (or more accurately, it will regress back towards the new mean based on a population without the susceptible to cold individuals). Now, that genetic variation you get from generation to generation might reach new extremes that it never would have gotten to during times of plenty.

This is an incorrect conclusion:

> In other words, the next generation will genetically regress to the mean.

Mating is emphatically not like mixing paints.

> [T]he Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem, or law, states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.

https://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_princip...

Isn't the Hardy-Weinberg principle basically regression to the mean?

It really depends on whether you can select from variation within the existing population, where the genetic variants already exist, in which case it can happen very fast, or if you are evolving net-new functionality (opposable thumbs), which can take anywhere between millions of years and eternity.

Evolution where genetic drift results in distinct species would take generations and necessarily some time

Reminds me of a line that Philip Glass co-opted for his 5th Symphony:

“Therefore the land mourns, and all who dwell in it languish, and also the beasts of the field and the birds of the heavens, and even the fish of the sea are taken away.”

Meat: To Eat It or Not - Philip Glass

https://tricycle.org/magazine/meat-eat-it-or-not-philip-glas...

https://web.archive.org/web/20250321203216/https://tricycle....

A very poetic and spiritual take, however IMHO he missed the elephant in the room for the compassion argument: breeding is much more cruel than killing by the harsh, prolonged condition. The killing in comparaison is nearly instant and arrive as a relief of that condition. Both comes together though and only considering the quicker and "natural" one isn’t fair.

What I've had heard so far about cod's troubles in the Baltic sea is that it's not salty enough for them. For cod to reproduce, their eggs need a certain salinity so that they swim to the right depth after they are spawned.

Here's an article in Latvian news site about it - https://nra.lv/neatkariga/intervijas/481931-mencu-zveja-balt...

The traditional approach to this problem is to harvest males and let females go. You're not going to select them out of sexual reproduction.

You will see males evolve to resemble females more closely, though.

The fish trap will have to be quite elaborate... maybe hang Playcod centerfolds in them?

Reminds me of the tuskless elephants.

https://www.nationalgeographic.com/animals/article/wildlife-...

What's impressive is that somebody, somewhere keeps collecting a nice stash of Eastern Baltic cod otoliths in hopes that somebody else would come along and invent a new way to use them.

These types of time series are super important, but hard to finance as they often only yield cool papers after decades.

Are there any 'old fashioned' cod in captivity or maybe stored DNA samples? Maybe Collosal could splice the missing genes back in and bring them back into the gene pool.

If there is a survival advantage to larger cod (presumably there is, or they would not have developed) and if fishing is tightly regulated, they should return eventually.

Not necessarily — the “large” genes could literally have been extracted from the gene pool.

It’s possible for them to mutate back into existence, but that’sa lower-probability, much longer proposition than if the genes are still available and just selected against.

* I meant "extincted" from the gene pool -- auto-correct un-corrected me...

Or, instead of wooly mammoths, bring back fishy ones.

This is about Eastern Balic cod, so theoretically genes from, for example, Norwegian cod could be spliced in. However body size is usually a polygenic trait with potentially hundreds of genes involved, so that's not possible.

If you catch by weight, does it matter how big the fish is? A ton of cod is a ton of cod.

It is easier to design nets that only catch big cods and don't also catch too much garbage.

We need to make certain parts of the world- unfishable- as in drag-net destroying pylons on the sea-floor, the waters mined with drones that attack any boat entering with the intent to fish. Its the only thing working against the international lawlessness picking the planet clean.

How are the drones going to recognize intent?

Spoiler: because overfishing altered their genes

Overfishing didn't alter their genes. It altered the genepool.

To be fair, that is the subtitle, "Eastern Baltic cod grow to much smaller sizes than they did just 30 years ago, because overfishing altered their genes, according to new research"

Yea, modern day journalists have really poor education and brainrot :/

The overfishing altered the allele frequencies of certain genes.

Actually directly altering the genes would have to involve mutation or direct engineering which is a bit more involved.

I think a good way to think about this is with human dwarfism. Many humans with achondroplasia get it through de novo mutation, but some get it by a combination of having two recessive loss of function genes that get transmitted by both parents (often of normal height)

Now imagine a laser beam that went and killed every human above a certain height. Young people would be spared along with adults with dwarfism. Over many generations, previously rare genes for dwarfism would increase in frequency shifting the average height of the population lower and lower.

It is the change in frequency that matters here more than the underlying explanation of what changed the genes.

Thanks for this cod piece.

Regression?

Modernity/Capitalism supercharges the hate Christianity has for nature, and well take out the earth with ourselves in the process soon.

Hail the great anthropocene.

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