How long for ocean life to recover?

Everybody out of the pool. If people were to get out of and off of the ocean–no fishin, no cruisn’ no playin’ no fightin’–how long would it take for sea life to return to populations comparable to where they were in, say, 1400? Big whales, crabs, cod fisheries, mermaids, etc.

Let’s leave the river running salmon alone as well, and obviously climate may preclude a 100% restoration given reef collapses and such, but let’s work around/with that.

In 1400 the North Sea whale population was well on the way to extinction. Humans and their precursors have been using the oceans for perhaps a hundred thousand years.

Based on that math it shouldn’t take long at all.

On a smaller scale, in the 60s Pittsburgh’s three rivers were pretty much dead. Then, the steel industry died, conservation efforts were made, and the rivers rebounded. Today the Allegheny, Monongahela, and Ohio are completely different waters.

Not sure how I got there, but not long ago I stumbled upon the “Timeline of the far future” Wikipedia article. In it, it estimates the recovery of the coral reef ecosystems from human-caused ocean acidification at 2 million years.

While one could think that fisheries wouldn’t take all that long, the story of the NW Atlantic cod is depressing.

So much disruption has taken place that it’s not clear if full recovery will ever happen.

The North Sea cod recovered during WW2. Present-day fishing restrictions, along with off-shore wind farms and oil rigs have contributed greatly to the current recovery.

Many of the fish, invertebrate, and marine mammal stocks will never recover to the levels they once were at before the industrial-scale impacts we’ve had, even if humans and all our current impacts on the seas could be pulled out like skimming toys out of the tub. Many species and populations have become functionally extirpated and/or displaced by other species more resilient to our impacts.

That’s not to say overall aquatic productivity and species abundance wouldn’t go up and get to similar biomass levels previously seen, but the species structure would certainly be different as we’ve had huge impacts on genetics of various populations, and recovery would look different in different areas.

Imagine a wheat field being left alone for the next hundred years; no tilling or re-seeding. It will be green again next summer, but certainly not with the native mature prairie species it had for thousands of years prior. It would take a long time to restore that kind of environment in the middle of a grain farming area. And some of the agronomic species we’ve introduced are so competitive with native species that they can permanently out-compete the successional species that naturally transform a landscape. I’ve seen photos of a simple cutline planted to grass in the middle of forests where the grass persists for decades with little to no sign of trees returning. Oceans and mobile species can be far more impacted by change.

So, in some areas some marine stocks may well recover to very high levels in 5-10 years, but other areas and populations recovery is hopeless and their place would be filled with other species which may explode to numbers never seen before, which would lead to a bunch of up/down cycles before leveling out somewhere a century or two later… but whatever that composition looked like it’s unlikely to look the same it did before we started having major impact.

That’s a good point.

Therefore, let me amend: the goal is similar biomass in an ecosystem roughly as stable as what existed before we got industrial on it. If there is a meaningful difference in the biomass-stability equation, err toward stability.

An all-jellyfish ecosystem could be super-stable, with similar biomass. But I wouldn’t want to swim in it.