> 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.

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)

> ruining the gene pool

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