The effects of environment and fishing on the abundance and condition of Iceland scallop (Chlamys islandica) in Breidifjordur

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Sea temperature is one of the primary factor limiting the overall geographical range of most marine species, including the Icelandic scallop. In Iceland, the sub-arctic Icelandic scallop resides at its southern limits. As a result, it is likely to be especially vulnerable to changes in the immediate environment. During the last 5 years, the stock size of Iceland scallop in Breidifjordur on the West coast of Iceland has un-dergone a dramatic decline. This period has been characterized by steady increase in summer sea temperature and in 2003 the temperature had reached a historical maximum of the last century. As well, since 1998, there have been fluctuations in chl-a level, with the lowest values observed in 1999 and 2000. At the same time, muscle weight has declined and a minimum weight was attained in 2001-2002. In the following years, natural mortality of scallops in Breidifjordur increased signifi-cantly. The mortality was however quite localized within the main fishing area in the southern part of Breidifjordur. At the same time two Coccidia parasites have been described in Iceland scallop from Breidifjordur. These parasite may have influenced the survival of the scallops. Recruitment into the fishable stock in Breidifjordur was highly variable during the 1993-2003, with low recruitment towards the end of the 1990’s. Due to high total fishing mortality during the 1990-2000, the fishery depended on relatively few year classes. Therefore the fragile status of the stock did not endure the medium-high exploitation rates in conjunction with several years of poor recruitment.