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USGS Geological Research Activities with U.S. Fish and Wildlife Service

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Burrowing activities of Chinese mitten crabs in San Francisquito Creek: an assessment of stream bank substrate, burrowing effects, and sediment erosion

Map of San Francisquito estuary.
Chinese mitten crab sightings since 2001. Source: U.S. Fish and Wildlife Service mitten crab monitoring database.

The Chinese mitten crab is one of the most successful of the recently introduced species to the San Francisco estuary. It was first detected in the San Francisco Bay in 1992. Distribution expanded rapidly throughout the estuary and river systems over the next few years. The crab is unique because adult crabs reproduce in brackish or salt water in winter and juvenile crabs migrate upstream to freshwater in spring. Mitten crabs reside in freshwater for as long as five years. In late summer and fall, mature adults begin to migrate downstream to brackish water, where they reproduce. They die soon after reproduction.

Mitten Crab.
Photograph of Chinese mitten crab.

 

Why are Chinese mitten crabs of interest? Chinese mitten crab burrows can cause slumping and enhance stream-bank erosion. Because the crabs have no natural predators in California, they also have impacted the water-supply pumping system to southern California by clogging the pumps.

Mitten crabs form extensive burrow networks in intertidal and fresh water habitats, in sediment ranging from mud to gravel to indurated sandstone. They undermine stream- and river-bank stabilization projects by extensive burrowing underneath riprap.

 

 

Mitten Crab burrows in a stream bank.
Mitten crab burrows in indurated gravel (top) and sandstone (bottom) in alluvial fan deposits, bank of San Francisquito Creek.

Several organizations are working together to understand different aspects of mitten crab biology, ecology and behavior in the San Francisco Bay-Delta system.

  • USGS is conducting a study of burrowing impacts by mitten crabs in San Francisquito creek. This work is partly funded by the USFWS.
  • Collaborating researchers in California have developed and refined a life history model of the Chinese mitten crab.
  • USFWS, with support from the Interagency Ecological Program, is conducting a survey to determine the distribution and relative abundance of the Chinese mitten crab in the San Francisco Bay and its tributaries, the delta, and the Sacramento and San Joaquin rivers and their tributaries. This survey includes sampling of field sites to assess mitten crab habitat preference and appropriate monitoring methods. USFWS has a reporting system that allows the public to report crab sightings.