SPECIES AT A GLANCE Chinese Mitten Crab (Eriocheir sinensis) Notch Four spines Hairy claws The Chinese mitten crab (Eriocheir sinensis) is a burrow­ ing crab that has a catadromous lifecycle, meaning it spends the majority of its life in the freshwater reaches of coastal watersheds, and reproduces and develops in brackish and saline estuaries. This crab can significantly transform the aquatic ecosystems it invades, through its intensive burrowing activities and high-density popula­ tions, which alter food webs and the physical habitat. The carapace is up to 4 inches in width and light brown in Carapace width: 3 inches Brandon Smith Brandon color, with a notch in the middle, between the eyes. The REPORT THIS SPECIES! claws have white tips and a dense patch of fur-like setae, Oregon: 1-- 866 INVADER or OregonInvasivesHotline.org Washington: 1- 877 -9 -INFEST or www.invasivespecies.wa.gov which gave this crab its name. California: www.wildlife.ca.gov/Conservation/Invasives/report Species in the news Learning extensions Resources “Fishing column: Beware of Mitten Crab Lab, available at USDA species profile:www.invasive ­ Chinese mitten crabs,” by Martin MenaceToTheWest.org speciesinfo.gov/aquatics/mitten­ Armstrong. www.sfgate.com/default/ crab.shtml article/Fishing-Column-Beware-of­ chinese-mitten-crabs-190826.php Why you should care How they got here and spread The Chinese mitten crab threatens ecosystems, earth­ The Chinese mitten crab was first identified in the en structures, and fisheries by preying on and compet­ south San Francisco Bay in 1992 by commercial ing with many species, including fish eggs, clams, and shrimp trawlers, and quickly spread to the Sacramento mussels; and by eroding riverbanks, wetland edges, and San Joaquin Rivers. It was introduced either ac­ and levees. It is an intermediate host of lung flukes cidentally through ship ballast water or intentionally from the genus Paragonimus (P. ringer, P. westermani), as a food source. which can infest humans and other mammals if raw or What you can do improperly cooked crab is consumed. As of now, the other intermediate host, Assiminea parasitologica (AP Clean all bilge and bait wells, fishing nets, and other snail) is not found in the same region as the Chinese gear before moving to new water bodies. It is illegal, mitten crab. If the two hosts were in overlapping habi­ under the Federal Lacey Act, to import eggs or live tats with the parasite, it could fully mature and cause a specimens of any species of mitten crab to the United serious health concern. States. It is also illegal to import, transport, or possess live Chinese mitten crabs in California, Washington, and Oregon. COOL FACTS The most identifiable feature is the dense patch of setae that looks like tufts of hair on its white-tipped claws. The purpose of these “furry” mittens is still unknown. Juveniles can adeptly walk on land and migrate upstream a hundred miles or more, climbing over obstacles such as small dams or dikes. Data on map represent established population and species occurrence. Map Synonyms: Shanghai crab, river crab, mitten crab created 2/14 by USGS. This fact sheet is part of Aquatic Invasions: A Menace to the West! A Toolkit Linking Science, Community, and Action through Education. SPECIES IN DEPTH ChineseChinese Mitten Mitten Crabs Crabs Chinese Mitten Crab Eriocheir sinensis Carrie Culver Carrie Culver Stephan Gollasch, Gollasch Consulting Gollasch, GollaschStephan Consulting NATIVE AND INVASIVE RANGE ECOLOGY The Chinese mitten crab is native to the coastal Habitat and food webs rivers and estuaries of the Yellow Sea in China Mitten crabs can survive a large range of salinities. and Korea. It has been introduced and spread Larval development requires a water temperature throughout the San Francisco Bay watershed of at least 9°C to survive, with an optimal range of and has migrated as far inland as the Sierra 15–18°C. They are omnivorous and eat vegetation, Nevada foothills of California. Range expansion detritus, mollusks, crustaceans (amphipods, water fleas, along the west coast is expected. A single male and shrimp), fish, and aquatic insects. Japanese mitten crab was caught in the Colum­ bia River in 1997, although no Chinese mit­ Life stages ten crabs have been captured yet in Oregon or The Chinese mitten crab is unique because it spawns in Washington. The sightings are usually reported saltwater and matures in freshwater (catadromous life by fishermen, because Chinese mitten crabs are cycle). This is opposite to species like salmon (anad­ known to be aggressive bait stealers. romous life cycle). The crab spends most of its life in UNITED STATES freshwater, then migrates to saltwater to reproduce. DISTRIBUTION These massive migrations have clogged fish hatchery equipment and hampered water delivery in Northern In the United California. The mitten crab is reported to mature in States, the species is 2–3 years in San Francisco Bay. Development can established only in California, although it has been reported in the Detroit River, Mississippi River, Great Lakes, Gulf Coast, Chesapeake Bay, and Columbia River. Amy Benson, USGS Amy West coast distribution of the Chinese mitten crab. Data on map represent established population and species oc­ currence. Map created 2/14 by USGS. Amanda Slade Aquatic Invasions! A Menace to the West • SPECIES GUIDE 3 Chinese Mitten Crabs Brian Tsukimura Brian Tsukimura Chinese mitten crab shipment found at the Shanghai Airport. COOL FACTS range from 1–5 years, depending on water temperature. Females carry eggs until hatching, and both sexes die The most identifiable feature is the dense patch of soon after the reproduction process. setae (or “fur”) on its white-tipped claws. The purpose The furry claws are usually a distinguishing feature of these “furry” mittens is still unknown. The adult is of the Chinese mitten crab, although the purpose of sexually dimorphic (the male looks different from the these “mittens” is still unknown. (Matt Bentley, New­ female); the male crabs have more setae on their claws than the females. castle University). Based on DNA studies, the Chinese mitten crabs found How it got here in the San Francisco Bay are actually from Germany. The most likely mode of transportation is their intro­ This means that the Chinese population established in duction as larvae through ballast water of ships from Germany and then was transferred to San Francisco Bay from there. Europe. They may also have been introduced on purpose (via Juveniles can migrate upstream a hundred miles or luggage on planes) to start a fishery. more, and can climb over obstacles such as small dams or dikes. How it spreads Mitten crabs are considered a delicacy in Asia, and are The Chinese mitten crab was first identified in the even sold in vending machines—alive! But they are rare south San Francisco Bay in 1992 by commercial shrimp because many of the waters in Asia are polluted and trawlers, and quickly spread to the Sacramento and San human consumption outstrips availability. Joaquin Rivers. A female can carry 250,000–1,000,000 eggs. Ocean currents and ballast water are capable of spreading the planktonic larvae of this species to new 4 Aquatic Invasions! A Menace to the West • SPECIES GUIDE Chinese Mitten Crabs coastal areas. It can also spread inland though river systems and canals. It is currently found throughout the San Francisco Bay watershed and has migrated as far inland as the Sierra Nevada foothills of California. Range expansion along the west coast is expected. Ecological impacts The Chinese mitten crab is an opportunistic feeder that preys upon a wide variety of plant and animal materials, making it a predator and competitor with native flora and fauna for limited habitat and resources. Burrowing causes significant erosion damage to Carrie Culver levees, stream banks, and irrigation structures. The Mitten crabs trapped in a fish diversion channel. crabs also burrow in soft-sediment banks, which could increase the frequency of flooding events, thus increas­ ing erosion and repair expenses. The mitten crab disturbs commercial and recreational fishermen by stealing bait, feeding on catch, and getting caught in nets. The spiny carapace and legs can damage fishnets. In their native range, young Chinese mitten crabs consume young rice shoots. Economic impacts The crabs burrow for shelter and protection from preda­ tors, which weakens levees and increases erosion of banks. The crabs are known to eat the eggs of salmon, trout, and sturgeon, possibly posing a serious threat to the vitality of ecosystems and fisheries along the west coast. The most common economic impact of the Chinese mitten crab has been the result of large numbers (up to 200) caught in shrimp trawling nets, which not only damages the nets but consumes time in picking them out and damages the shrimp to the point where they are unsuitable for the bait market. As the crab population grows and spreads across the Bay, it becomes more dif­ www.chinahush.com www.chinahush.com ficult to avoid unintentionally catching them. Considered a delicacy in China, live mitten crabs are sold on the Health hazards street in vending machines. This machine is located in a subway station, and it also sells small bottles of vinegar that people use to The crab is a host to the human lung fluke parasite. The season their crab. For a story on crab vending machines, see www. fluke also needs an alternate host to complete its life chinahush.com/2010/10/26/crab-vending-machines-in-subway­ cycle: an invasive snail called Assiminea parasitilogica station/ (or the “AP snail”). The AP snail is not currently found in the San Francisco Bay with the mitten crab; however, Aquatic Invasions! A Menace to the West • SPECIES GUIDE 5 Chinese Mitten Crabs Crabzilla! In the fall of 1998, as many as 1 million mitten crabs were collected at the federal and state fish salvage facilities in the south part of the Sacramento–San Joaquin River Delta in California.