Fish too much, and you get fewer fish. That’s neither new nor surprising, but a new study suggests that overfishing’s depletion of fish populations can have permanent effects. Quartz reports:
By removing one of its species, overfishing “flips” an ecosystem into an “alternative state,” explains the University of Maine’s Robert Steneck, one of the report’s authors. It sets off a complex reshuffling among remaining species. Often, this “locks” the ecosystem into a “alternative stable state”—meaning, the species of fish can’t come back.
The Benguela ecosystem off the southwest coast of Africa recently underwent one such “flip” as a result of overfishing. Where once sardines, anchovies, and mackerel were plentiful, jellyfish now choke the waters. Overfishing of sardines and anchovies and the larger fish they supported led to a phytoplankton bloom. These drifting microorganisms are a key feedstock for aquatic ecosystems, but in large quantities they can deplete oxygen in the water to levels unsustainable for fish, which is what happened in Benguela. Jellyfish thrive in these hypoxic conditions, and have come to dominate this particular system. And, because jellyfish eat fish eggs, there’s a feedback system in place to keep jellyfish stocks high and fish stocks low.That’s a very rough sketch of one ecosystem, and it shows just how difficult to understand and predict the effects of culling or removing even one member in a food web. Nature finds a way to rebound, but often it’s a way that isn’t in our best interest. It isn’t enough to simply stop fishing when fish populations dwindle to the point that it’s no longer economically viable to send the boats out, and then just wait in hopes that fish stocks will then recover. There may already be a large vacuum in the ecosystem, which can be filled by something we’d rather not eat, like jellyfish.This isn’t some unicorn hunt—it’s a green fight actually worth fighting. Responsible management of fisheries is in our own best interest.