Blue whiting - A key species in the mid-water ecosystems of the north-eastern Atlantic

Blue whiting (Micromesistius poutassou) is a mesopelagic gadoid that is widely distributed in northeastern Atlantic from the Canary Island to Spitsbergen. It is abundant and commercially exploited in the Norwegian Seas, off Iceland, Faeroe Islands, Hebrides and Ireland, and in the Bay of Biscay. Blue whiting is a highly migratory species. During the spawning season (March-April), blue whiting concentrates to dense aggregations on the well-known spawning locations along the shelf edge west of Ireland and Hebrides and in the Rockall area. Other spawning areas also exist, but stock structure, distribution and migration of this abundant species are insufficiently known. The oceanic distribution of blue whiting westward, towards the mid-Atlantic Ridge (MAR), has not been thoroughly investigated. Scattered observations show that the species occurs along the MAR from the Azores in the south to the Reykjanes Ridge in the north. The possibility that blue whiting is a key species in the mi-water community of the MAR should not be dismissed. Where present, blue whiting is often highly abundant, and plays an important role in the pelagic ecosystems, both as a consumer of zooplankton and small mesopelagics, and as a prey for larger fish and cetaceans. Is there a 'stock' of blue whiting over the MAR? If yes, is this stock separate from the stock(s) in the northeastern Atlantic? Institute of Marine Research in Bergen has proposed a component project of MAR-ECO that combines routine monitoring information with observations from the MAR-ECO surveys to evaluate the significance of blue whiting in the pelagic ecosystem of the MAR. We present the available background information, along with hypotheses being tested. We also describe some of the methodological and technological challenges.