Patterns, efficiency and ecosystem effects when fishing Calanus finmarchicus in the Norwegian Sea — using an individual based model

Abstract Diets of Norwegian spring-spawning herring, mackerel, and blue whiting in the Norwegian Sea are investigated in relation to the distribution of plankton and hydrographic conditions. Fish stomachs and zooplankton samples were collected during summer (June and July) cruises in 2001 and 2002. Calanus finmarchicus was the principal prey of mackerel, accounting for 53–98% of total stomach content by weight. The diet composition of herring varied depending on feeding area and availability of food under various environmental conditions. C. finmarchicus was important prey for herring only in July 2001 (about 77% by weight) in the central part of the sea and in June 2002 (about 82% by weight) near the Lofotens. In July 2002 appendicularians (Oikopleura spp.), amphipods (mainly Parathemisto abissorum), and euphausiids were important in the diet of herring, and at some stations cannibalism was observed. The main prey of blue whiting were amphipods (10–34% by weight), appendicularians (11–34%), and euphausiids (8–47%), as they usually feed deep in the water column, though C. finmarchicus was important, particularly in June 2002, when blue whiting were caught in the upper layers of the sea. Higher water temperatures indirectly affect pelagic fish through accelerated development of their prey and favourable conditions for migration farther north.

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Distribution of overwintering <i>Calanus</i> in the North Norwegian Sea

Ocean Science Discussions ◽

10.5194/osd-3-25-2006 ◽

2006 ◽

Vol 3 (2) ◽

pp. 25-53 ◽

Cited By ~ 3

Author(s):

A. Edvardsen ◽

J. M. Pedersen ◽

D. Slagstad ◽

T. Semenova ◽

A. Timonin

Keyword(s):

Seawater Temperature ◽

Calanus Finmarchicus ◽

High Abundance ◽

Survey Area ◽

Norwegian Sea ◽

The North ◽

Copepod Abundance ◽

Shelf Slope ◽

Annual Changes ◽

The Difference

Abstract. During winter 2003 and 2004, zooplankton and hydrographic data were collected in the northern parts of the Norwegian Sea (68–72° N, 8–17° E) west of the Norwegian shelf break at depths down to 1800 m. The results cover both inter and intra annual changes of hydrography and distribution of Calanus spp. For the whole survey area, average seawater temperature down to 1000 m was higher in 2004 than in the same period in 2003. For the upper 500 m the difference was ca. 1°C. Calanus finmarchicus dominated at ca. 75% of the total copepod abundance. Typical abundance of C. finmarchicus in the survey area was 30 000–40 000 m−2. C. hyperboreus was found deeper than C. finmarchicus while other copepods were found at the depth of C. finmarchicus or shallower. From January to February 2004, the peak of abundance of C. finmarchicus and C. hyperboreus shifted ca. 300 m upwards indicating that ascent from overwintering depth took place at a speed of 10 m d−1 during this period. In general, high abundance of copepods was found adjacent to the shelf slope while oceanic areas had low and intermediate abundance. In the southern part of the survey area, location of high and low copepod abundance shifted both between and within years. In the northern part of the survey area where the shelf slope is less steep, copepods was present at intermediate and high abundance during all surveys.

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