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The brown spots on the lobster shell indicate shell disease. In addition thorough lab-tests are necessary before a probable diagnosis can be made.      
Photo: Egil Karlsbakk
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Lobster found to have shell disease

All of the evidence suggests that one of the sick lobsters handed in to The Institute of Marine Research last autumn is suffering from epizootic shell disease. Scientists are disturbed that the disease, which has not previously been seen in lobsters in Norway, appears to have been introduced with American lobsters.

By Marie Hauge

“This is an environmental crime. The American lobster is a species that doesn’t belong here. Now we know that it is bearing disease with it, which shows how serious the situation is,” says scientist Nina Sandlund, who has been heavily involved in examining the sick lobsters. The Institute of Marine Research has now embarked on a programme of controlled experimental fishing in the Larvik area to find out whether there are more lobsters with the disease.

From the fjord and aquariums

In late autumn last year, The Institute of Marine Research received four lobsters with varying degrees of shell damage. Two of the lobsters had been caught in Viksfjorden, in Larvik Municipality. The two others had spent 4-5 years in aquariums in Ålesund and Drøbak respectively.
Our scientists suspected that the lobsters might be suffering from a shell disease that had not previously been found in lobsters in Norwegian waters. The disease causes the lobster shell to rot away, and in the most serious cases it is fatal.

Outbreaks of shell disease have effectively stopped lobster fishing in several parts of the US, where the disease has spread rapidly over the past decade.

Not widely researched

Genetic tests soon confirmed that three of the four specimens were American lobsters. Live American lobsters are imported to Norway for consumption, and individuals that were caught in the wild may have escaped from holding pens or have been illegally put out.

The latest test results support the scientists’ suspicion that they are suffering from shell disease.

“The tests that we have carried out so far suggest that we are dealing with epizootic shell disease. This is based on bacteriological and histological tests, and the visible signs of the disease on the shell,” explains Nina Sandlund.

To perform thorough tests on a lobster it must be killed, so the researchers are not yet in a position to say for sure whether the three other lobsters have the disease.
Little is known about the disease; for instance it is not known whether it is contagious and, if so, how it is transmitted. Whether shell disease spreads by contagion or due to other factors will make a crucial difference to our European lobster populations, which have so far avoided the disease.

Importance of experimental fishing

Sandlund emphasises that further specimens must be examined before we can reach any definite conclusion about the disease and the situation in Norway. At least 150 lobsters are needed to give scientists an indication of whether the disease is widespread amongst the American lobsters that live along the coast of southern Norway. It will also be very interesting to find out whether the disease exists in European lobsters.

The Directorate of Fisheries has given permission for controlled experimental fishing to remove any other American lobsters and hybrids from the Larvik area. Local fishermen will catch the lobsters. All lobsters that are caught will be DNA-tested and examined for signs of disease. Lobsters identified as being American, hybrids or diseased will be removed. The remainder will be tagged and put back where they belong.

“But even if we don’t find any European lobsters with the disease, we can’t be sure that the disease isn’t contagious,” emphasises Nina Sandlund.
The disease takes time to develop, so it will be some time before the results of the experimental fishing are known. 

Facts on shell disease in American lobsters:

Epizootic shell disease:

  • Probably contagious, caused by chitin-degrading bacteria.
  • This disease has caused the rapid proliferation of shell disease among lobsters on the east coast of the USA.
  • It has so far failed to implement "Koch's postulate," that is, isolate and identify a specific bacteria that cause disease.

Enzootic shell disease:

  • Not / probably not contagious between individuals.
  • Speculations are made of whether there are contaminants that may be the primary cause of the injuries seen on the skin (lesions)