Home / Environment / Mitten Crab Invasion: SF Bay's Furry Invader Spreads West
Mitten Crab Invasion: SF Bay's Furry Invader Spreads West
28 Aug
Summary
- Chinese mitten crabs, first seen in 1992, became a notorious invasive species.
- They are catadromous, living in freshwater but breeding in saltwater.
- Confirmed sightings in Oregon mark a significant expansion of their range.
A small, fur-clawed creature, first identified in San Francisco Bay in 1992, has become one of the West Coast's most notorious invasive species: the Chinese mitten crab. Native to East Asian rivers, this crab likely arrived in ship ballast water.
Initially found in the San Francisco Bay estuary, mitten crabs proliferated rapidly, causing issues with water pumps and levees. By 1998, hundreds of thousands were recorded. The population in the Sacramento-San Joaquin Delta later declined mysteriously, with no live specimens confirmed in California since 2010.
Despite a West Coast population lull, mitten crabs appeared in East Coast bays and the Hudson River. Their catadromous nature—living in freshwater but breeding in saltwater—facilitates wide colonization. Burrowing capabilities and tolerance for pollution make eradication difficult.
In April 2025, a commercial fisherman caught a mitten crab in Oregon's Lower Columbia River, the first confirmed regional sighting. A second was found in November in the Willamette River, marking the species' first confirmed foothold in the region over three decades after its initial U.S. appearance.
