Chinese mitten crabs (Eriocheir
sinensis) - a threat to Washington State's waters?
The Management Model
The Management Problem
The topic of this paper is in general terms the introduction of
aquatic nuisance species (ANS) into domestic waters and more specifically
the threat of the Chinese mitten crab (Eriocheir sinensis [pic], H.
Milne-Edwards 1854) for
Washington's waters. It is the
first of three parts of a term project with the respective objectives of
1. identification of the current management
structure and regulations,
2. evaluation of the ecological assumptions inherent in the
3. recommendations for institutional changes and further
their natural habitat
with naturally limiting factors like food source and predators
in other parts of
world. One danger of introduction of ANS is that native
species are removed or outcompeted and
ANS become predominant. The goal of managing
ANS is therefore to prevent
introduction in the first place, and where already established to limit or
reduce their actual numbers.
The Chinese mitten crab is a
catadromous, burrowing [pic
] species native to
China’s and Korea’s coasts in the Yellow
Sea (Cohen/Carlton 1995). The crab
was first collected outside its natural habitat in Germany in 1912,
supposedly introduced via ballast water. In the 30s the crab became
abundant with devastating effects on dams, levees and river
banks (Slack 1996) [pic] fishers
claimed that it also damaged their catch and gear (Panning, 1938).
spread over the northern parts of Europe, but population
explosions like in the 30s have not occurred again.
In the 80s Chinese mitten crabs were available as a
delicacy in seafood markets in Los Angeles and San Francisco
(Cohen/Carlton 1997). The crab
was subsequently banned in
California (Section 671(h)(2) Title 14 CCR) for concerns about its
possible physical impacts on dams, as well as its potential
threat to human health (Horwath 1989)[details]
(note: the crab can be secondary host
for the Oriental lung fluke, Paragonimus westermanii [details], which can generate - sometimes
fatal - tuberculosis
symptoms). By 1989 US regulation
(50 CFR 16.13) listed the crab as an injurious
species rendering its importation and possession a crime.
However, in 1992 a live Chinese mitten crab was described
in the San Francisco
Bay area; by 1994 it was well established there (Cohen/Carlton,
1997; Halat/Resh, 1996); and in 1997 it was found as far north as the
Columbia river (Seattle Times, A 8, 28 January, 1998). With an established
and growing population in the San Francisco
Bay (Veldhuizen/Hieb, 1998) (in addition to the possible introduction from
Asia or Europe) an invasion of Washington State's waters becomes more and
likely. Therefor, the crab is listed in the draft of the Washington State
Nuisance Species Management Plan as one of four freshwater species that
pose the greatest threat to environment and economy
(working draft 1998, unpubl.).
The management model [
figure 1] describes the
potential vectors for the introduction and dispersion
of the Chinese mitten crab in US
to the point
where it actually can cause harm and therefore is considered to be a
Once the crab has reached the
shores, it can
invade freshwater systems and eventually establish a population.
impacts [table 1a and description] of the crab on humans
and the ecosystem, like dam and levee destruction, fish and gear damage,
and the assumed disturbance of the trophic cascade, can occur at any stage
of its dispersion in fresh and brackish waters (for impacts in accordance
with different lifestages see table
Management actions relate to the vectors of the introduction. ANS
into US waters over various avenues, which can be roughly divided into
intentional and unintentional introductions. Unintentional introduction
occurs when ballast water from vessels is dumped in order to load
cargo; some when ANS dwelling on the hull of a vessel
are scraped off or when they spawn in US waters; ANS may also come as part
of a shipment either directly or in package material for live seafood or
other "target species" (pets), which is then disposed in the local waters.
Intentional introduction includes scientific research and testing, biological
control, i.e. the attempt to reduce another ANS by introduction of a
natural predator, species for aquaculture production, and pets.
As third category one might consider natural invasion, i.e. the migration
of animals (or plants) in different waters where there was previously no
possibility, for example through a newly built canal.
Various theories exist for the introduction of the Chinese mitten crab
into US waters [table 1b], but
just two are considered to be the likely transport mechanism: ballast
water and "intentional private-party inoculation to establish a food
resource" (Cohen/Carlton, 1997)(note: the crab was sold in
California as a delicacy; mitten crabs were
intercepted at airports in Los Angeles, San Francisco and Seattle and
petitions for mitten crab aquaculture have been submitted to the
legislature, Cohen and Carlton 1997).
(Legal) introduction for research and
testing - the crab is scientifically interesting because of its salinity
tolerance - is
limited through the permit system established by federal laws (see
Natural invasion of
US waterbodies from, for example, San Francisco Bay might happen through
the crabs' migration.
When transported to domestic waters ANS can cause
which are basis for environmental concerns and
(subsequently) management actions. The Chinese mitten crab is a
nuisance for humans in
the following ways:
1. as a parasite host,
(Veldhuizen/Hieb, 1998; Cohen/Carlton 1997; Halat/Resh 1996).
2. through its burrows, i.e. increased erosion and weakening of dams,
3. its clogging of intakes at pumping stations and power plants, and
4. its damaging impacts on fishers' catch and gear.
see table 1a and also table 2a
Its impacts on the ecosystem
are not fully understood
but it can
be reasonably assumed that it affects the food chain in similar ways other
ANS do, i.e. imbalancing the trophic cascade as a food competitor and/or a
Possible management actions encompass regulation and
education with the aim of controlling and eradicating the
vectors of introduction. Both
and unintentional introduction can be restricted by some legislative act
if the necessary enforcement is in place. Since authoritative regulation
and enforcement is never a 100% measure and compliance will always be
lacking, education is an important additional factor. Education is
most desirable on the assumption that individuals are not only willing to
comply if they are sufficiently aware of the problem but also contribute
to prevention and abatement through voluntary action.
The introduction of the Chinese mitten crab is generally regulated by
the legislation on non-indigenous species (50 CFR 16.13, "Importation
of live or dead fish,
mollusks, and crustaceans, or their eggs") by which the "importation,
transportation, or acquisition of ... live mitten crabs ... is prohibited"
except in cases of permissions for scientific, medical, educational, or
zoological purposes (50 CFR 16.22). Enforcement of these regulations is
delegated to different US authorities [table
1b], thus a permit for an import of Chinese mitten crab
for scientific purposes has to be obtained from the Fish and Wildlife
Washington has legislation in place that covers nuisance species
general, and the Puget Sound Exotic Species Task Force works on a policy
proposal that includes measures relating to the Chinese mitten crab more
specifically (workdraft 1998, unpubl.).
In addition to the existing injurious species US legislation mentioned
above, there is proposed regulations for ballast
water exchange on a voluntary basis and for mandatory reporting and
sampling procedures, (Department of Transportation, Coast Guard, 33 CFR
Part 151) to comply with the National Invasive Species Act of 1996
(Federal Register, vol. 63 (69), 17782).
On an international level IMO has adopted measures that
propose the exchange of ballast water at sea. These, however, are not
legally binding and in the IMO guidelines it is observed that the exchange
may be a threat to safety when it has to be done in adverse weather
conditions; this added to the assumed unwillingness of ship operators to
undertake more than is absolutely necessary, the exchange of ballast water
on a voluntary basis is unlikely to be of great effect.
Publications like Gordy Slack’s article, "Chinese Crabs Discover San
Francisco Bay" in the summer issue of Pacific
Discovery in 1996, are part of an unstructured educational effort not
focused on a particular state. Through articles like this the
public awareness can be influenced and perhaps a change in behavior
The desired outcome of management action is to reduce or limit the
threat which the Chinese mitten crab poses to human health, to
fisheries, to riverbanks and dams by closing the introduction vectors.
Regulation is the only reasonable measure for ballast water exchange
since education alone cannot reach addressees from abroad satisfactorily.
Education and regulation may interrupt other vectors, especially where the
main actors operate from within the US, i.e. aquaculture and seafood
marketing. Regulation works for shipping and mailing standards, as well as
for aquaculture. But as soon as the vectors cannot be overseen by official
enforcement authorities, education should supplement prevention measures,
i.e. once ANS are pass the border controls and in the hands of private
individuals, regulations alone are as weak as the addressees and without
education (or intense and costly enforcement) they might be less than
Although legislation renders capture and possession a crime the effect is
less than satisfactory: Cohen and Carlton (1997) indicate that intentional
private-party introduction happens nevertheless, and a Chinese mitten
crab population could establish itself in the San Francisco Bay Area by
1994 despite California's ban from 1987.
Under the current management model it is assumed that crabs are only
introduced from foreign sources (ballast water, shipping/packing),
management of established population is not in place and the problem of
the Oriental lung fluke is only addressed as part of the mitten crab
problem. An overview of the management goals and actions is
depicted in figure 2.