Chinese mitten crabs (Eriocheir sinensis) -
a threat to Washington State waters?



Robyn Draheim, Jamie Goen, Florian Wegelein

 Assignment 3C
June 3, 1998
SMA 510: Ecological Concepts for Decision Makers




Management Recommendations
Priority Actions for Management
Figure 3a. Stages of nonindigenous species invasion

Research and Monitoring Needs

Impediments to Management






Established in San Francisco Bay as well as Europe, Great Britain and Asia, the Chinese mitten crab, an aquatic nuisance species native to Korea and China (Cohen and Carlton 1995), may well be poised for an invasion of the estuarine and fresh waters of Washington State. In the summer of 1997, an adult mitten crab was caught in the Columbia River (Henderson 1998). This is the northernmost appearance of the crab to date and evidence of the growing threat. The Washington State Aquatic Nuisance Species Planning Committee considers the mitten crab, a catadramous, burrowing crab averaging 6-8 inches in diameter, to be "one of four [freshwater] species pose[ing] the greatest threat to Washington's environment and economy." Currently, management is aimed primarily at reducing the undesirable outcomes of a mitten crab invasion by limiting their introduction into US waters. As such, it does not adequately address the possibility of the establishment, spread, and impacts of a mitten crab invasion especially from infested waters within the US.

Presently, many of the regulations and strategies now being devised to slow the introduction of zebra mussles and green crabs into Western waters target general concepts and behaviors that are not specific to those two species but also include mitten crabs and aquatic nuisance species (ANS). Other regulations and strategies need to focus on ecological knowledge of priority organisms, such as mitten crabs, whose invasion is imminent.

The first two assignments in this three part term project identified and examined the assumptions implicit in the current management model (Assignment 1) and evaluated them in light of the underlying ecological model detailing the life history of the crab and identifying the stages at which establishment, spread, and impacts occur (Assignment 2).

The objective of the third and final assignment of this term project is to take both the management and ecological models into account and recommend further scientific research, regulatory revisions, future courses of action, and management options. Recommendations include institutional changes and areas where scientific research would amend or expand the management model and fill in the uncertainties of the ecological model. In addition, certain areas where conflicting interests impede the use and application of ecological knowledge will also be identified.



Management Recommendations

The current mitten crab management goal is aimed at reducing the threats of physical destruction, fisheries damage, adverse ecological interactions, and health hazards associated with the introduction of Chinese mitten crabs into US waters. Achievement of this management goal in Washington State, a region facing but not yet experiencing a mitten crab invasion, is hindered as there are few regulations that address either directly or indirectly the introduction of the mitten crab into Washington. The management model assumes a foreign source of mitten crabs and that the regulations which address the elected vectors are adequate to prevent invasion. The management model also assumes a simplified ecological system and does not adequately address the life history of the mitten crab. In addition, there is a great deal of scientific uncertainty reflected in both the management model and the ecological model that must be eliminated in order to provide managers with more information to work with to effectively address the mitten crab threat. Recommendations include combining into the management model elements which were extrapolated from a review of management actions and ecological knowledge (or lack thereof) from areas that are dealing with or have dealt with mitten crab invasions and infestations of other nonindigenous species (NIS).

Exotic species are an ongoing threat to Washington State and US waters. The problem of NIS introductions could be best managed by an overarching legislation and educational policies rather than on a species-by-species basis. Managing NIS on a species-by-species basis is not effective in addressing open transportation vectors. However, NIS policies and legislation should be adaptive in order to take into account impending introductions into Washington State waters. The threats posed by the mitten crab, green crab, and zebra mussel, are best handled on a basis that takes into account the specific ecology of the species involved, to tailor an effective management plan. Here too there may be room to combine monitoring and educational efforts for species that have similar life-history traits, like mitten crab and green crab volunteer monitoring in estuaries and zebra mussel and mitten crab exclusion devices over intake pipes. Many such species do have similar or overlapping life history characteristics that can be addressed, and this in turn may be useful in the development of the overarching legislation as well. For example, preventive measures may limit vectors that are important for other NIS.


Priority Actions for Management:

The following management recommendations apply to the four stages of invasion of aquatic nuisance species:

Figure 3a. Stages of nonindigenous species invasion (adopted from Olson and Linen, un pub).  


Progressing from transportation to impacts in the diagram above, there is a decrease in funding for, ecological knowledge of, and understanding of the problem (Olson and Linen, un pub). Conversely the cost of control and erradication increases. The following management recommendations are based on the progressive lack of understanding at each stage.



Although transportation vectors are well studied and many have controls, with the expansion of global free trade it will become increasingly important to further address these in order to lessen the impacts of NIS. Nonindigenous species and especially ANS have to be taken into consideration when negotiating trade agreements. For example, the US and individual states must have measures in place to close, regulate, or minimize transportation vectors prior to trading.

The problem of unintentional invasion can be addressed more effectively from both sides of the vector, thus ballast water might be taken on in the foreign country in a place where NIS are less abundant or ships might just take on fresh water. Other solutions for the ballast water problem might be electro-pulse, ultraviolet treatment, biocides, filtering, deoxygenation, or magnetic fields. Additional possibilities along those lines should be explored for their feasibility. Until this technology becomes available ballast water exchange must be mandatory for everyone entering Puget Sound, Columbia River, and other Washington State waters from both national and international destinations. National and international transportation vectors should be closed or minimized with inspections and quarantines. Education also plays an important role in closing vectors of introduction.

Vectors other han ballast water must be addressed. To effectively do so, these vectors must be qualified and quantified to assess their transport potential. Vectors such as shipping and packing materials, scientific research specimens, importation of live seafood, and intentional introductions will require a joint strategy of education and regulation to control introductions.



The health of natural habitats should be improved to insure their resiliance to NIS. Promotion of habitat integrity will lessen the risk of anthropogenic disturbances providing opportunities for invasive species establishment. Healthy, functional ecosystems provide the best defense against exotic invaders.

In the event that invasions are imminent, emergency control strategies must be developed a priori to invasion to inhibit or slow the establishment of thriving NIS populations.



The possibility of secondary invasions through intentional and unintentional interstate transportation and watershed by watershed transportation must be addressed. Some of these are already covered by regulations, such as intentional transport and possession and simply need more effective enforcement measures. Other secondary invasions, like natural range expansion and establishment, need to be taken into consideration in management strategies.



Management strategies, such as intake pipe exclusion devices and traps, should be in place to reduce ecological and physical impacts. When the above actions have failed to be successful some sort of abatement measure must be in place to mitigate the impact on the domestic environment. At this stage that can only happen by physical reduction of the numbers. Traps at dams, for example, can take advantage of the mitten crab’s behavior of crawling on land whenever it encounters an obstacle (Panning 1938). The crabs can then be collected and processed.



Research and Monitoring Needs

The scientific uncertainties detailed in assignment 2 and to a lesser extent in assignment 1 must be addressed in order to effectively manage the Chinese mitten crab and prevent further introductions. Due to the need for a substantial amount of basic scientific research on the mitten crab's life cycle and ecology, the research and monitoring needs will be prioritized based on the gap in ecological knowledge as well as the likelihood of available funding and institutional support.



Impediments to Management

Efforts should be made to reduce, if not eliminate, current impediments to management efforts. Among the many existing impediments are costly management actions and regulatory improvements in institutions traditionally resistant to change. Institutional structures are reluctant to implement long-term plans if the immediate benefits of such immediately apparent. Even though it would be less costly for management to address the problem of NIS before they invade, institutions often trade-off for a risk of much higher management costs in the future.

In addition, there exist a multitude of state and federal agencies that are charged with addressing NIS issues (OTA 1993). There is no centralized agency with the authority to coordinate regulatory actions or enforce existing regulations. This lack of centralization leads to lack of collective action or fragmented and often contradictory policies between agencies.

There is a general lack of knowledge among institutions and the general public regarding the problems of NIS which impedes the implementation of NIS management. The basic ecology of mitten crabs in particular is very limited, although a few exotics such as the zebra mussel have been well studied and brought to the attention of the general public.

Effective management requires a balance between the socio-economic and institutional costs and benefits of actively closing all possible vectors of NIS introductions. For instance, while regulations requiring the mandatory open ocean exchange of ballast water for all vessels would significantly reduce NIS introductions, the issue of vessel safety is a higher priority. Therefore, efforts may need to be concentrated at other possible solutions to removing NIS from ballast.

 It is very costly to significantly reduce uncertainties in scientific knowledge. However, management decisions made without complete information risk greater costs in the long-term.




The Chinese mitten crab does pose a threat to Washington State waters. Without a comprehensive management plan based upon ecological knowledge and the impacts of NIS, and more specifically the Chinese mitten crab, efforts to prevent and slow the introduction and spread of this nuisance species will continue to be limited, at best, in their effectiveness. As the resolution of scientific uncertainty improves, managers will have more complete information available to them for use in prioritizing issues and determining acceptable levels of socio-economic and environmental risks and trade-offs.

It is not known whether or not a mitten crab invasion of Washington State waters will be similar to the invasion of Germany or that of San Francisco, or if it will be completely different altogether. Taking a precautionary approach, is advised, utilizing extrapolated information where available, supporting research and monitoring efforts, and controlling and/or closing as many vectors as possible. Another important management approach is education. Education should be used as a management tool to reduce impacts of NIS through increasing public awareness and modifying human behaviors that contribute, intentionally and unintentionally, to the introduction and spread of NIS.