Marine Biology

, Volume 150, Issue 6, pp 1253–1263 | Cite as

Vertical distribution and mortality of Calanus finmarchicus during overwintering in oceanic waters southwest of Iceland

  • Astthor GislasonEmail author
  • Ketil Eiane
  • Pall Reynisson
Research Article


The seasonal vertical distribution and the predatory regime encountered by Calanus finmarchicus were studied along a transect across the Reykjanes Ridge in the oceanic area southwest of Iceland from data collected during four cruises between November 1996 and June 1997. The mortality for the overwintering period was estimated using linear regressions of density estimates from November 1996 to April 1997. In addition, we also estimated the mortality of the oldest population stages (C4 and older) in April and June by applying the vertical table method. During winter (November/December–January/February), the animals mainly resided at a depth of ∼300–1,500 m in the water of Atlantic origin. Ascent to upper layers took place mainly during March and April, and continued until May. During all cruises, continuous deep-scattering layers were observed, mainly within the range of 400–500 m to 700–800 m depth. Based on sampling with a Harstad pelagic trawl in April, the scattering was mainly ascribed to jellyfish (mainly Periphylla periphylla), small mesopelagic oceanic fishes (several species but Benthosema glaciale and Maurolicus muelleri were most abundant), euphausiids (mainly Meganyctiphanes norvegica) and shrimps (mainly Sergestes arcticus). These species may represent a predatory threat to overwintering C. finmarchicus. From November to April, daily per capita mortality rates were estimated to be (mean ± 95% CL) 0.004 ± 0.0028 for the total data set, and 0.004 ± 0.0033 and 0.004 ± 0.0023 (day-1) for the Iceland Basin and Irminger Basin, respectively. Mortality rates were higher later in life (mean ± 95% CL) for C5/females (0.13 ± 0.044) and C5/males (0.19 ± 0.051) than for C4/C5 (0.00 ± 0.035) when averaged over all samples taken in April and June 1997. We discuss how the observed distribution and mortality rates of overwintering C. finmarchicus might be related to predatory regime.


Mesopelagic Fish Reykjanes Ridge Predatory Regime Iceland Basin Scattering Layer 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We are grateful to the crew on the RV “Bjarni Sæmundsson” and colleagues at the Marine Research Institute for their help in the sampling. Further, we should like to thank A. R. Bodvarsdottir and H. Petursdottir for analysing the zooplankton samples, and H. Valdimarsson, J. Morthensen, and S.-A. Malmberg for help with the interpretation of the physical data. This study was funded by the European commission through the TASC project (Contract No. MAS3-CT95–0039) and the Icelandic Republic Fund. A substantial part of this paper was written during a 2-month visit of the first author to the Woods Hole Oceanographic Institution on the invitation of Dr. Peter Wiebe whose hospitality is gratefully acknowledged.


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Marine Research InstituteReykjavikIceland
  2. 2.University Courses on SvalbardLongyearbyenNorway

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