Abstract
Change in oceanographic conditions causes structural alterations in marine fish communities, but this effect may go undetected as most monitoring programs until recently mainly have focused on oceanography and commercial species rather than on whole ecosystems. In this paper, the objective is to describe the spatial and temporal changes in the Barents Sea fish community in the period 1992–2004 while taking into consideration the observed abundance and biodiversity patterns for all 82 observed fish species. We found that the spatial structure of the Barents Sea fish community was determined by abiotic factors such as temperature and depth. The observed species clustered into a deep assemblage, a warm water southern assemblage, both associated with Atlantic water, and a cold water north-eastern assemblage associated with mixed water. The latitude of the cold water NE and warm water S assemblages varied from year to year, but no obvious northward migration was observed over time. In the period 1996–1999 we observed a significant reduction in total fish biomass, abundance, mean fish weight, and a change in community structure including an increase in the pelagic/demersal ratio. This change in community structure is probably due to extremely cold conditions in 1996 impacting on a fish community exposed to historically high fishing rates. After 1999 the fish community variables such as biomass, abundance, mean weight, P/D ratio as well as community composition did not return to levels of the early 90s, although fishing pressure and climatic conditions returned to earlier levels.
Highlights
The Barents Sea ecosystem has been considered ecologically ‘healthy’ [1,2] and many of the commercial fish stocks, especially the Northeast Arctic cod (Gadus morhua), are in good shape [3]
Field Study Data on fish species abundance and biomass for 82 fish taxa were collected during the former annual shrimp surveys conducted by the Norwegian Institute of Fisheries and Aquaculture (NIFA) and the Institute of Marine Research (IMR) in the Barents Sea from 1992 until 2004, when the shrimp survey was terminated
The pelagic/ demersal (P/D) ratio increased (Fig. 2e), revealing that the fish community has become more dominated by small pelagics after
Summary
The Barents Sea ecosystem has been considered ecologically ‘healthy’ [1,2] and many of the commercial fish stocks, especially the Northeast Arctic cod (Gadus morhua), are in good shape [3]. Local temperature increase in the Barents Sea is expected to lead to migration of Atlantic fish species northwards [5,7,8], but more complex and structural community changes may occur [9,10,11]. Single species responses may not give a good indication of possible changes in the ecosystem due to the large inter-annual variability of single stocks, and because fishing may conceal climate change effects [13]. Change in climatic conditions and fishing have been the most important drivers for structural change in marine ecosystems [14], for instance as seen in the previously cod-dominated community in the NW-Atlantic [15]
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