Invasion
Invasion Description
1st Record: CA/South San Francisco Bay (1992, Cohen and Carlton 1997)
Mitten Crabs were abundant at the Tracy Fish Collection Facility in Byron, CA every year from 1996 to 2005, but only single individuals were observed in 2006, 2009, and 2010. No crabs have been observed in California since 2010 (Steven Foss, personal communication (3/28/18). The absence of recent records is paralleled both on the East and West Coasts, but it is possible that populations are persisting at low levels of abundance. For now, we will treat the population as established.
Geographic Extent
CA/South San Francisco Bay (1992, Cohen and Carlton 1997); Petaluma/CA/Petaluma Creek, San Pablo Bay (1994, USGS Nonindigenous Aquatic Species Program 2006); Port Chicago/CA/Suisun Bay (1994, USGS Nonindigenous Aquatic Species Program 2006); Hatfield State Rec. Area [N of Gustine)/CA/Merced River (1998, USGS Nonindigenous Aquatic Species Program 2006); Kern National Wildlife Refuge/CA/Tulare-Buena Vista Lakes watershed (2005, USGS Nonindigenous Aquatic Species Program 2006); Colusa National Wildlife Refuge/CA/Sacramento River watershed (2005, USGS Nonindigenous Aquatic Species Program 2006)
Recent observations: Cosumnes Preserve/Mokelumne City/CA/San Francisco Delta (9/23/23, i-Naturalist https://www.inaturalist.org/observations/183171045, photo of burrow); Pedro Point/CA/Pacific Ocean (4/27/2019. https://www.inaturalist.org/observations/23309231, phoot of animal)
Vectors
| Level | Vector |
|---|---|
| Alternate | Ballast Water |
| Alternate | Fisheries Intentional |
| Alternate | Fisheries Accidental (not Oyster) |
Regional Impacts
| Economic Impact | Fisheries | |
| In some areas of San Francisco Bay and European waters, interference by crabs with bait has made fishing unpleasant or impossible (Chinese Mitten Crab Working Group 2003; Invasive Species Specialist Group 2006). Sport fisheries in San Francisco Bay have a total annual value of about $2 billion per year (Chinese Mitten Crab Working Group 2003), so fishing losses in parts of the Bay can have a substantial economic impact. In addition to bait-stealing, dense populations of Mitten Crabs also interfere with traps, nets and aquaculture ponds, by clogging them and breaking them, and by eating trapped fish (Chinese Mitten Crab Working Group 2003; Invasive Species Specialist Group 2006). In California, E. sinensis caused serious mortality in fish-salvage facilites, designed to divert fish from irrgation faclilities in the Sacramento-San Joaquin Delta. At peak migration times, mortality of migrating fish in 1998 was 98-99%. Retrofitting of the facilities to prevent mitten crab entrapment was expensive (Rudnick et al. 2000; Chinese Mitten Crab Control Committee 2003). Mitten Crabs can also intefere with fisheries by competing for food and shelter with fished species such as crayfish and shrimp in San Francisco Bay (Chinese Mitten Crab Control Committee 2003). | ||
| Economic Impact | Shipping/Boating | |
| Erosion and riverbank collapse due to burrowing can affect canals and shipping channels (Chinese Mitten Crab Working Group 2003). | ||
| Economic Impact | Industry | |
| Industry (Power plants)- Large numbers of migrating crabs have clogged the cooling sytems of power plants in Europe and California, reducing water flows (Chinese Mitten Crab Working Group 2003). Industry (Agriculture)- Chinese Mitten Crabs are reported to damage rice plants in China, and pose a threat to rice fields in California. Their ability to burrow in canal banks and clog irrigation systems can pose serious problems for irrigation-dependent agriculture (Chinese Mitten Crab Working Group 2003). | ||
| Ecological Impact | Predation | |
| Eriocheir sinensis is an opportunistic omnivore. Juvenile and adult crabs feed on detritus, algae, aquatic plants, invertebrates, and dead or trapped fish. Stable isotope, gut contents, and feeding studies in San Francisco Bay indicate that this species feeds heavily on aquatic derived detritus, algae, and invertebrates feeding on the sediment surface. Dense populations of mitten crabs could alter stream communities by decreasing abundance of surface-dwelling invertebrates and shifting invertebrate populations to deeper dwelling infauna (Hymanson et al. 1999; Rudnick et al. 2000; Rudnick and Resh 2005). Mitten crabs are not normally fish predators, since they are slow-moving, but in confined spaces such as fishways, and holding-tanks in power plant and irrgation systems, they can attack fish or cause mortality through sheer crowding and clogging of passageways. In California, they caused serious mortality in fish-salvage facilites, designed to divert fish from irrgation faclilities in the Sacramento-San Joaquin Delta. At peak migration times, mortality of migrating fish in 1998 was 98-99% (Rudnick et al. 2000; Chinese Mitten Crab Control Committee 2003). Direct predation on fish eggs in spawning streams (for example, eggs of the Steelhead Trout (Oncorhynchus mykiss)), is a concern in the San Francisco Bay area (Chinese Mitten Crab Control Committee 2003). | ||
| Ecological Impact | Competition | |
| Chinese Mitten Crabs are potential competitors with other crustaceans in estuarine and freshwater habitats for food and space. Non-native species which could be affected include Orconectes virilis (Virile Crayfish) and Procambarus clarkii (Red Swamp Crayfish), both are established in Chesapeake Bay tributaries. In San Francisco Bay tributaries, diets of E. sinensis and P. clarkii overlapped somewhat, but E. sinensis feeds more on detritus of aquatic origin, algae, and surface dwelling invertebrates, while P. clarkii feeds more on detritus of terrestial origin and deeper-dwelling infauna (Rudnick and Resh 2005). | ||
| Ecological Impact | Habitat Change | |
| Juvenile Eriocheir sinensis (Chinese Mitten Crabs), in their native and introduced habitats, create extensive burrows in the banks of the tidal portions of streams. Burrows in South San Francisco Bay tidal streams ranged from simple tubelike holes to complex, many-branched systems with multiple entrances, but all sloped downward from the entrance, so that they retained water after high tide. In different areas, total burrow volume averaged 700-900 cm-3 (Rudnick et al. 2005b). Burrowing crabs ranged from 4 mm to 45 mm carapace width, and burrow diameter was about twice the crab's carapace width. Overall, in the study area, burrows removed 0.8 to 5.7% of the stream bank sediment (Rudnick et al. 2005b). This extensive burrowing in steep creek banks creates increased erosion, slumping, and sometimes collapse of river banks. In man-made levee and dike systems, Mitten Crab burrows can increase the frequency of catastrophic flooding during rain events and contribute to the loss of tidal wetlands. | ||