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Impacts of a reduced thermohaline circulation on transport and growth of larvae and pelagic juveniles of Arcto-Norwegian cod (Gadus morhua)

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A reduction of the thermohaline circulation (THC) might have strong impact on Northeastern Atlantic fisheries. We address this potential challenge by studying the effects of THC changes on larval drift and development of Arcto-Norwegian Cod (ANC, Gadus morhua), as several studies have shown that there is a close link between the abundance and individual size of cod at the 0-group stage and the year class strength of the 3-group fish. The approach taken is that of a modelling study supported by analysis of existing data on fish stocks and climate. A regional model (ROMS) is forced by a global climate model (Bergen Climate Model-BCM) in which the river runoff to the Nordic Seas and the Arctic Oceans is increased by a factor three over the present day value, causing the THC to slow down. Although this increase in river runoff is extreme, the simulated response might be applicable in explaining and interpreting possible processes and feedback mechanisms of relevance for ANC. The impact of the anomalous circulation and ocean temperature on ANC in its habitat as simulated by ROMS is studied by using an individual-based model to simulate growth of the larvae and pelagic juveniles along their simulated drift paths. The present description of a reduction in the THC by 35% results in: (1) a southward and westward shift in the distribution of cod year classes from the Barents Sea onto the narrow shelves of Norway and Spitsbergen, (2) a reduced individual growth of the pelagic juveniles, (3) an increasing number of larvae and pelagic juveniles advected towards the western parts of Spitsbergen, and possibly further into the Arctic Oceans where they are unable to survive.

Keywords: Arcto-Norwegian cod; distribution; dynamical downscaling; growth; ocean model; thermohaline circulation

Document Type: Research Article


Affiliations: 1: Institute of Marine Research, PO Box 1870 Nordnes, N-5817 Bergen, Norway 2: Nansen Environmental and Remote Sensing Center, Thormøhlensgt. 47, N-5006 Bergen, Norway

Publication date: May 1, 2007


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