Around the world, fishermen use low-cost nets that sit like fences on coastal seafloors. Known as set gill nets, this type of gear is highly effective at catching fish when the mesh snags them by their gills. But gill nets also catch a host of other species by mistake.

In California, decades of commercial sea bass and halibut fishing killed thousands of other coastal animals (as many as 300 harbor porpoises per year may have been killed!). Outraged by the deaths of sea otters and diving seabirds, voters in the state banned many of the nets from near-coastal waters starting in 1994.

The harbor porpoise, which is actually one of the smallest toothed whales on Earth, is a very secretive animal and difficult for marine biologists to count, but there has been such a marked increase that success is obvious.

The rebound could almost be considered an understatement. Since the bans were introduced, harbor porpoise populations have added about 8,200 new members, in Monterrey Bay, Morro Bay, Santa Barbara, and the San Francisco and Russian River systems.

It’s a significant triumph for the hidden marine mammal, which in Morro Bay alone grew from 570 individuals in 1990 to more than 4,000 in 2012 (a seven fold increase!).

"Harbor porpoises show that if you stop killing them, thank you, they can return. That they're capable of recovering," Karin Forney, a research biologist at the National Oceanic and Atmospheric Administration, said. "They have a resilience and they will rebound if we just let them."

Source: LA Times

https://www.latimes.com/projects/porpoise-rebound-after-california-ban-gill-fishing-nets/