Americans on the wrong side – the lobster Homarus americanus captured in Norwegian waters

Abstract

In November 1999, two female lobsters, one with external egg batch, were captured in the common lobster fishery in the Oslo fjord, Norway and reported as possible American lobsters, Homarus americanus, to Bergen Aquarium and the Institute of Marine Research. More, but undersized specimens were said to be present in the fishery. After this six more American lobster has been captured on other part of the Norwegian coast, both escapees from people importing them illegally from abroad. Some were banded, or showed sign of recent banding. Closer inspection confirmed that the two individuals first registered showed a series of American characteristics, as a ventral tooth on the rostrums, longer and sharper teeth inside the cutter claw and the typical greenish-brown colour common in American lobsters. Tissue sample from additional four specimens were analysed by starch gel electrophoresis and all possessed new alleles, never reported in European lobster before, at several allozyme loci. These alleles correspond to common alleles in American lobsters as demonstrated in a reference sample. Origin and time of invasion of the American lobsters are suggested, as well as possible ecological interactions and influence on the original lobster population when invaded by this competitor.