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Comment by pvaldes | Hacker News Reader

I'm sceptic about that, specially after reading this.

> All the species in which older, bigger fish are found in deeper water have something else in common: we eat them

Hemm, not. Poisonous fishes show the same pattern. There are poisonous fishes also in the deep sea. If we do not eat then, why do not live in the surface?

Mola mola is the biggest extant bony fish. Is neither fished nor eaten normally. Adults still pass most of its time at deep waters.

To extrapolate the behaviour of 30.000 species of animals after one single species and one single variable leads often to wrong conclusions. Fishes are complex creatures.

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Are you just saying that there are poisonous deep sea fish?

To be a counterexample it needs to be a poisonous fish that exists in shallow waters but whose older members only occupy deep waters. Entirely deep-sea species aren't what this article is referring to. I'm not aware of any poisonous fish that aren't hunted by humans that follow this pattern.

Just saw your edit. I don't think that sunfish fish of different ages spend their time at different ocean depths? Wasn't mentioned on wikipedia.

Many deep-sea fishes have buoyant eggs and larvae that can reach the photic zone. Even the species that do not reach the photic zone live in shallower areas when younger.

A lot of pelagic fishes start their life at 1cm under the ocean surface also.

The paper (which admittedly I only skimmed, so someone correct me if I'm wrong) seems to indicate that only around 70% of the variance based on a simulation (and I believe historical data) was due to fishing. The remainder could very well be ontogenic. So it's entirely possible that fishing is only one factor in this phenomenon.

Mola mola dive deep to eat various kind of jellyfish: https://www.sciencenews.org/blog/wild-things/lazy-sunfish-ar...

Also, bycatch can reduce the populations of large fish that aren't actively fished or eaten.

Therefore some fishes could have good reasons to inhabite deep waters different than the article's bold assumption that "All fishes dive deep to not be eaten by humans".

Mola mola is a fish, therefore this would lead us to "Mola mola dive deep to not be eaten by humans" that is a false statement.

When you’re fishing solo or at scale, you don’t really have a choice as to which fishes get caught up in your nets or on your hook.

But that one species has had tremendous impact on fish populations, so could easily impact the evolution of fish.

I think he meant cod as the one species, not humans, since the study only looked at cod populations and not any other fish.

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