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

> 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

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.

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

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

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.

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

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)

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

> ruining the gene pool

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

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.

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.

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 Shrinking for Decades; Scientists Have Answer

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.

> 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.

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

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.

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.

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.

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

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.

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

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

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 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.