Posted by littlexsparkee 19 hours ago
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.
> 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.
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
The article says smaller fish could more easily escape the nets. Though it doesn't cite studies documenting that, it does seem reasonable.
The grinder doesn't care what size the fish are.
In what sense? 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.
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.
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.
This is not even a little bit true.
This farming runoff overload has also led to huge areas where the sea floor is completely dead.
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...
Personally, I believe that mosquitos are far more concerning than any other impending environmental disaster.
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.
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.
Pertains to Eastern Baltic cod, not all
Or, still fitting:
Scientists Find Eastern Baltic Cod Shrank due to Overfishing Affecting Genepool
“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.”
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.
It might sound like a boring topic, but it's one of the best books I've read and something I recommend a lot.
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.
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
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.
> 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...