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.
> 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.
> 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.
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
>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
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)
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.
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.
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.
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.
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.
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.
> 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.
