Zooplankton biomass and species distribution is monitored during the joint autumn ecosystem survey. Joint Russian and Norwegian zooplankton investigations have taken place since 2002. Regular sampling by IMR began in 1979 while PINRO has conducted these surveys since in 1982-1993. A Juday net (37 cm in diameter, 180μm) is used to obtain zooplankton samples by PINRO. IMR uses a WP2 net (56 cm in diameter, 180μm) and a 1m2 MOCNESS multiple plankton trawl with 9 nets all having a mesh size 180 μm, as standard zooplankton gears.
The MOCNESS is mainly used for obtain better data on the vertical distribution of mesozooplankton and the gear is also somewhat more efficient with regard to the larger zooplankton components like arrow worms, krill and amphipods.
In 2005 comparisons were made between the Juday and WP2 net catches from the joint autumn cruises both with regard to biomass and species composition. The biomasses obtained by the two gears are quite similar. A report on the comparisons of the two gears was prepared at a joint meeting held at IMR in May 2006 and the EcoNorth symposium in Tromsø in March 2007. During the Ecosystem survey in August-September 2007 a specially designed double-net system, holding side by-side one Norwegian WP2 net and one Russian Juday net, was used to sample the water column at selected stations in order to compare the sampling efficiency of the two nets for various mesozooplankton components. A total of 19 hauls were conducted with the double-net system. Samples have been worked up for biomass comparisons, and a special workshop was arranged in Bergen 22-26 October 2007 where most of the samples were analyzed for species composition and abundance by Russian and Norwegian specialists. All double-net hauls were operated with a vertical speed of 0.5 m s-1 from RV G.O. Sars. The analyses from this work are in due progress and will be reported at a later stage.
Monitoring of zooplankton along the Fugløya-Bear Island section by IMR started in 1987 and are now conducted 5-6 times each year usually in January, March/April, May/June, July/August and September/October. In addition the Vardø-N section is sampled ~4 times a year. However, data prior to 1994 are scarce and does not give a full seasonal coverage. The WP2 plankton net has been used regularly during this monitoring since 1987. In addition vertically stratified MOCNESS tows are taken during the two-month Ecosystem survey in August-September each year, approximately one haul pr. day.
Regular macroplankton surveys have been conducted by PINRO in the Barents Sea since 1952. Surveys involve annual monitoring of the total abundance and distribution of euphausiids (krill) in autumn-winter trawl-acoustic survey. To collect macroplankton a net attached to trawl (trawl net) (0.2 m2 opening area, 564-mm mesh size) was used. This net is a modification of egg net IKS-80 and it is attached to the headline of a bottom trawl and catch plankton near the bottom. During winter, crustaceans are concentrated in the near-bottom layer and have no pronounced daily migrations, and the consumption by fish is minimal. Therefore sampling of euphausiids during autumn-winter survey is used to estimate year-to-year dynamics of their abundance in the Barents Sea. Annually 200-300 samples of macroplankton are collected during this survey, and both species and size composition of euphausiids are determined. It is necessary to note that in spite of quite a large mesh size, the net can catch both small and large animals (Orlova et al., 2004a,b). In August-September in the north-eastern areas in the bottom layer (6-10 m above the bottom) are observed of young Th. abyssorum in length from 0.5 mm up to 4-6 mm, and Th. libellula (length 3.5-12 mm), as well as unidentified young hyperiids 1-6 mm in length (60-150 and 320 ind./1000 m3).
Gelatinous zooplankton (ctenophores and cnidarians) are caught in both the WP2 net and the MOCNESS plankton trawl. However, it is questionable to which degree catches can be considered truly quantitative especially for the larger ctenophores and scyphozoans. In addition many species are damaged in nets. Thus their actual abundance can be severely biased. Since larger cnidarians of the class scyphozoa are also caught in the pelagic Harstad trawl used for 0-group fish and capelin we have chosen in this report to present catches from this trawl, normalized to kg•trawldistance-1, although caution should be exercised in their quantitative interpretation.
