Abstract
High Calanus finmarchicus abundances were recorded in wintertime in Vestfjorden, close to the main cod breeding grounds off Lofoten and Vesterålen, northern Norway. The mean abundance for locations with water depth >500 m was ∼37000 ind. m−2 (range: 26700–49000 ind. m−2). To our knowledge, this is the first report of massive overwintering of C. finmarchicus on the Norwegian shelf. Because of the observed size and location of this population, we argue that local overwintering on the northern Norwegian shelf can contribute significantly to sustain a C. finmarchicus population on the shelf during the period of first feeding for cod larvae. This is supported by a particle tracking model.
Highlights
The North Atlantic and subarctic holoplanktonic calanoid copepod Calanus finmarchicus is a key food source for many marine animals including the larval stages of cod (Gadus morhua) (Planque and Batten, 2000; Falk-Petersen et al, 2007, 2009; Heath and Lough, 2007)
We investigated whether overwintering populations of C. finmarchicus in a deep fjord basin close to historically important cod breeding grounds are large enough to significantly contribute to the origin of the shelf population; and if the main circulation pattern can lead to advection of this population toward the coast of the Lofoten
copepodite stage V (CV) abundances were estimated from the size class from 1.5 to 2 mm equivalent spherical diameter and validated by manual counts (Manual_count 1⁄4 0.87 Â ZooScan_count, R2 1⁄4 0.96, n 1⁄4 10)
Summary
The North Atlantic and subarctic holoplanktonic calanoid copepod Calanus finmarchicus is a key food source for many marine animals including the larval stages of cod (Gadus morhua) (Planque and Batten, 2000; Falk-Petersen et al, 2007, 2009; Heath and Lough, 2007). Deep fjords may provide suitable overwintering habitats for C. finmarchicus on the Norwegian shelves, but the relatively low abundances observed there in winter (Skreslet and Rød, 1986; Bagøien et al, 2001; Skreslet et al, 2015) suggest that many such populations may not be a significant food source for populations of cod larvae relative to the oceanic overwintering populations. We investigated whether overwintering populations of C. finmarchicus in a deep fjord basin close to historically important cod breeding grounds are large enough to significantly contribute to the origin of the shelf population; and if the main circulation pattern can lead to advection of this population toward the coast of the Lofoten
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