This is the main message in a risk assessment of eight species of crabs, which VKM has conducted on request by the Norwegian Environment Agency.

Background

Three of these species have previously been seized by customs, and these were most likely intended for the food and restaurant industry. The crabs were alive when they were transported into Norway from Sweden. Based on the seizures, the Norwegian Environment Agency decided to assess the risk such imports could pose to biodiversity in Norway. An additional five species, identified by the Institute of Marine Research as relevant as food, were included in VKM’s assignment.

Methods

VKM has reviewed available scientific literature on the relevant species and assessed what negative effects they could cause if they are released into Norwegian nature. VKM has also assessed how likely it is that the species could establish themselves in Norway. The risk posed by the crabs is thus determined by the effect they can have and the likelihood of this happening. In addition, VKM has proposed various risk-reducing measures. The effects and their likelihood together constitute the risk posed by each species.

VKM identified three factors that can negatively affect biodiversity. We have conducted risk assessments for each of these factors:

• Competition with native species

• Predation and grazing on native species

• Transmission of diseases

In addition, the establishment of some species, especially the Chinese mitten crab and Japanese mitten crab, and their behavior of digging burrows in riverbanks, can lead to structural changes in ecosystems.

Results

VKM’s risk assessment indicates varying risk levels for the different factors and species. We conclude that there is a high risk of negative effects due to competition and predation for two of the species, and medium risk for an additional five.

Regarding disease spread, there is a high risk associated with the two mitten crab species, and possibly high risk associated with the American stone crab. The diseases that pose the greatest threat are crayfish plague and gaffkemia, which affect freshwater noble crayfish and lobsters the hardest.

VKM also assesses that three of the species pose a moderate risk related to burrowing behavior.

Foreign crabs imported alive as food have a significant potential to establish themselves in sea and freshwater. The likelihood of establishment is high because the species are adaptable, some species can tolerate environmental conditions similar to those found in large parts of Norway today, and the species have a high reproduction rate, "says Gaute Velle, who has been professionally responsible for the assessment.

VKM has also made an overall assessment of the risk posed by the eight species if they are imported alive as food.

Especially diseases, which can also be spread by dead or dying crabs, are a concern," says Velle.

The potential for disease spread has therefore weighed heavily when the eight species were ranked. Overall, there is low risk for only two of the eight species, while there is high or possibly high risk for three species and medium risk for three species if the species are imported alive for use in the food and restaurant industry.

The risk assessment has been approved by VKM’s Panel on Biodiversity.