https://www.mercurynews.com/2020/12/02/big-increase-in-porpoises-off-northern-california/

In the 1980s and 90s, it was a grim trend off Northern California’s coastline: Hundreds of harbor porpoises, shy marine mammals that look like small dolphins, were killed every year in huge gill nets used by commercial fishermen.

The animals would wash up dead on beaches after becoming tangled in the nets, which stretched for up to half a mile underwater. After public outcry and threats of lawsuits from environmental groups, state officials banned gill nets in nearly all Northern California waters near the shoreline.