I don't know if there is a lot less fish than 100 to 10,000 years ago.
There is no doubt that a lot more fish are being fished than compared to 100 or more years ago.

Such areas as lakes one could easily say this. Or marine animals such a seals have been drastically reduced.
Though such marine animals as seals and whales could be increasing there numbers in last few decades- though probably never return their peak levels.

Fish like salmon, has been affected by humans preferring to live in coastal regions and disrupting their spawning areas- but it's possible that salmon hatcheries have mitigated this effect. It's possible that because salmon are a "commercial crop" that they could be too many salmon- just as there are too many cows [or cats and dogs].
I have heard that cod is much less abundance, nor do know of anyway humans could significantly increase cod populations.

It seems to me that it would quite easy to increase the lower food base in which fish depend upon for higher populations. And of course as I posted before, I think we should have more fish farms in the open oceans.

Of course not everyone is particularly fond of eating fish, but I find some kinds of fish to be fairly tasty.

But if humans like to eat something, history has shown that creature usually won't have problem in terms of having lower population.