Abstract
The deep scattering layers of the North Atlantic, including the Irminger Sea, contain many predators of the key copepod species Calanus finmarchicus. Previous seasonally restricted studies have described the deep acoustic scattering layers of the Irminger Sea as ‘ubiquitous’. They have shown that the intensity of the acoustic backscatter varies across the region, and so, by implication, the potential predation pressure on C. finmarchicus also varies spatially. This paper reports observations of the distribution of epi-pelagic (0–200 m) and meso-pelagic (200−1,000 m) acoustic backscatter in the Irminger Sea, made using a scientific echosounder operating at 38 kHz during four seasonal (winter, spring and summer) cruises. Our study demonstrates that the intensity of the backscatter varies seasonally in regionally distinct ways across the Irminger Sea. The mean acoustic backscatter, both in the upper 800 m and upper 200 m of the water column, varied significantly between the northern, central and southern areas of the central basin (‘open ocean’), and within each area between the Greenland shelf slope, open ocean and Mid-Atlantic Ridge subregions. Different patterns of seasonal change in the acoustic backscatter between the upper 800 m and upper 200 m were also seen, indicating both persistent differences in the underlying amount of backscatter in each area, and varying patterns of seasonal increase in the near surface backscatter in the different areas and subregions. These observations could be related to the different oceanographic regimes encountered in each location, and are discussed in terms of their implications for potential predation pressure on C. finmarchicus.
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Acknowledgements
This work was funded by the Natural Environment Research Council, UK under the Marine Productivity Thematic Programme. We wish to thank J. Hunter and all the members of the Fishery Independent Methods Group, FRS Marine Laboratory, Aberdeen for providing both equipment and invaluable technical support; and the Masters, officers and crew of RRS Discovery, along with the members of the scientific parties of each Marine Productivity cruise, for all their assistance at sea.
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Communicated by J.P. Thorpe, Port Erin
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Anderson, C.I.H., Brierley, A.S. & Armstrong, F. Spatio-temporal variability in the distribution of epi- and meso-pelagic acoustic backscatter in the Irminger Sea, North Atlantic, with implications for predation on Calanus finmarchicus. Marine Biology 146, 1177–1188 (2005). https://doi.org/10.1007/s00227-004-1510-8
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DOI: https://doi.org/10.1007/s00227-004-1510-8