26 May 2009

Are they a problem if people eat them?

Procambarus clarkiiA new report described in the Telegraph lists marbled crayfish as posing “high risk” to British wildlife if they are released into the wild.

This news story comes on the heels of two letters in the most recent issue of Science that offer a back and forth on the issue of introduced species. The first, by Gozan and Newton, talks about potential benefits of introduced species, like “aquaculture, sport fishing, forestry, horticulture, and game hunting.” The reply by Hulme and colleagues mentions crayfish as an example:

Major aquaculture species such as the crayfish Procambarus clarkii and Pacific cupped oyster Crassostrea gigas threaten endemic species through predation, competition, and/or the spread of diseases, and these two specific examples are widely recognized as some of the worst invasive species in the region(.) ... The history of biological invasions in Europe has too many examples of shortsighted decisions targeting perceived economic gains that have resulted in much larger (and often irreversible) costs to society. Thus, such “balance sheet” decision-making promoted by Gozlan and Newton, rather than a precautionary approach, is not only naïve but potentially dangerous.

This article on the National Science Foundation website has an related take on invasive species. It tracks students who were examining the impact of Louisiana red swamp crayfish (Procambarus clarkii) into China.

(W)e were surprised by how welcome this exotic crayfish was in the Chinese community, even among rice farmers whose crops were being destroyed. ...

Another rice farmer explained that if he had the necessary resources, he said he would sell only crayfish and eliminate rice farming all together.

Emphasis added. This is particularly relevant to Marmorkrebs, as it has been rumoured that they are being investigated for aquaculture purposes in China. Plus, asexual species in theory can generate double the number of reproductive offspring every generation compared to sexual species.

Thus, people could be extremely tempted to introduce Marmorkrebs into natural ecosystems deliberately. The problem is that such introductions have ended in tears as often, if not more often, than they have ended in triumph. (Two words: Cane toads.)

Harvested crayfish in Chinese fish market. Difficult to recognize, except for escapee in upper left!

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