Oh yes, for those who did ecological patterns and processes last year, the tall tale of the signal crayfish is back for this post after reading an article on the BBC website inspired a small investigation.
The American signal crayfish Pacifastacus lenisculus has been detrimental in the decline in native European crayfish species. With its introduction via commercial culture (Alderman et al 1990) it not only establishes itself as a more adaptable and therefore more prevalent species within freshwater ecosystems but its resistance to the crayfish plague has been the most dominant advantage it has over the European crayfish. Gren et al (2008) are one of many articles discussing the issue of the signal crayfish carrying this plague, caused by the oomycete, Aphanomyces astaci Schikora (Alderman et al 1984), which when introduced to a new area threatens native populations with extinction. Gren et al (2008) discuss this issue in relation to Sweden due to the association of crayfish with recreational and cultural traditions, such as a cuisine delicacy corresponding to 0.5kg/person/year, and the impacts that this has on the presence of non-native crayfish. Crayfish caught in Swedish lakes accounts for about 35% of the total consumption and the 65% left over is imported internationally. In Sweden alone, signal crayfish account for 85% of the total number of crayfish harvested, however harvesting is not the only way that the presence of crayfish is being appreciated; crayfish are being caught be recreational divers.
The signal crayfish was introduced into Swedish waters in the 1960's to compliment native crayfish populations as they were in severe decline, partly due to exploitation but also, due to the fungus plague. As stated by Gren et al (2008), the idea with the introduction was for the signal crayfish to replace the native crayfish and 'fill the ecological niche' that was left behind by the loss of the native species. The issue with this introduction in the 1960's was that the knowledge behind the transference of the plague, which had been present in Sweden since 1907(Unestam, 1969), was not entirely certain, and it was discovered that the signal crayfish was a carrier of the plague. With this revelation, signal and noble crayfish therefore could not co-exist in the same environment for this reason alone, let alone the physical dominance of the signal crayfish out competing the native noble and its increased mobility. This was confirmed by a study by Fiskeriverket and Natuvardsverket in 1998. This led to the imposition of regulations on the introduction of signal crayfish, however they were still being introduced by those who were able to obtain permits. The article concludes, after analyzing the impacts of economic factors on the occurrence of signal crayfish, that restrictions need to be imposed as the spread of the species is not likely to decrease from economic development, its spread can be described as independent from economic factors, the primary introduction alone was enough.
The article by Gren et all (2008) is one of many examples of how species in contemporary times have been facilitated to meet the increasing demands of the human population. This shows how the signal crayfish was purposefully introduced to supply the local populations of Sweden with a favoured delicacy. As to my previous post, this deliberate introduction has had dramatic implications on the populations of the local noble crayfish of Sweden, as Gren et al (2008) states, populations in areas have been driven to near extinction.
Alderman, D. J, Polglase, J.L, Frayling, M, Hogger, J. (1984) 'Crayfish plague in Britain', Journal of Fish Diseases 7. 401-405.
Alderman, D. J, Holditch, D, Reeve, I. (1990) 'Signal crayfish as vectors in crayfish plague in Britain', Aquaculture, 86, 3-6
Gren, Ing-Marie, Campos, Monica, Edsman, Lennart, Bohman, Patrik (2008), 'Incomes, Attitudes, and Occurrences of Invasive Species: An Application to Signal Crayfish in Sweden', Environmental Management, 43:210-220
Unestam, T. (1969) 'Resistance to the crayfish plague in some American, Japanese and European crayfishes, Report of Istitute Freshwater Research, 49, 202-209
The signal crayfish was introduced into Swedish waters in the 1960's to compliment native crayfish populations as they were in severe decline, partly due to exploitation but also, due to the fungus plague. As stated by Gren et al (2008), the idea with the introduction was for the signal crayfish to replace the native crayfish and 'fill the ecological niche' that was left behind by the loss of the native species. The issue with this introduction in the 1960's was that the knowledge behind the transference of the plague, which had been present in Sweden since 1907(Unestam, 1969), was not entirely certain, and it was discovered that the signal crayfish was a carrier of the plague. With this revelation, signal and noble crayfish therefore could not co-exist in the same environment for this reason alone, let alone the physical dominance of the signal crayfish out competing the native noble and its increased mobility. This was confirmed by a study by Fiskeriverket and Natuvardsverket in 1998. This led to the imposition of regulations on the introduction of signal crayfish, however they were still being introduced by those who were able to obtain permits. The article concludes, after analyzing the impacts of economic factors on the occurrence of signal crayfish, that restrictions need to be imposed as the spread of the species is not likely to decrease from economic development, its spread can be described as independent from economic factors, the primary introduction alone was enough.
The article by Gren et all (2008) is one of many examples of how species in contemporary times have been facilitated to meet the increasing demands of the human population. This shows how the signal crayfish was purposefully introduced to supply the local populations of Sweden with a favoured delicacy. As to my previous post, this deliberate introduction has had dramatic implications on the populations of the local noble crayfish of Sweden, as Gren et al (2008) states, populations in areas have been driven to near extinction.
Alderman, D. J, Polglase, J.L, Frayling, M, Hogger, J. (1984) 'Crayfish plague in Britain', Journal of Fish Diseases 7. 401-405.
Alderman, D. J, Holditch, D, Reeve, I. (1990) 'Signal crayfish as vectors in crayfish plague in Britain', Aquaculture, 86, 3-6
Gren, Ing-Marie, Campos, Monica, Edsman, Lennart, Bohman, Patrik (2008), 'Incomes, Attitudes, and Occurrences of Invasive Species: An Application to Signal Crayfish in Sweden', Environmental Management, 43:210-220
Unestam, T. (1969) 'Resistance to the crayfish plague in some American, Japanese and European crayfishes, Report of Istitute Freshwater Research, 49, 202-209
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