Harvesting marine cold water plankton species - abundance estimation and stock assessment

During the regular monitoring activity in the Norwegian Sea in the period 2013-2016 sampling in the Arctic waters of the western part of the Norwegian Sea has been undertaken with Macro-plankton trawl, nets, acoustics and standard environmental instrumentation. A good material for quantification of krill, amphipods and other macro-plankton were obtained. All available data by the Macro-plankton trawl from 2007 to 2015 is now quality assured. The analyses of the distribution and biomass of the dominant species of macro plankton and micronekton are close to finished. In May and June 2013 a fair amount of samples of macro-plankton were taken for Harvest II through the arctic fronts of the North Atlantic in connection with the transatlantic cruise organized by EUROBASIN. In the same areas, complementary high-resolution data on physical conditions, phytoplankton, zooplankton and fish were collected with the towed vehicle MESSOR. For the first time, we used a VPR (Video Plankton Recorder) on the vehicle for studying the abundance and species composition of small to medium-sized zooplankton that will be connected to optical particle data (OPC) and multi-frequency acoustic data in the upper 400m of the water column for the establishment of abundance estimates. Processing and analysis of the material is largely completed and the writeup for publishing is ongoing. During the transatlantic cruise, it was also made respiration measurements of Themisto libellula and T. compressa. Respiration was measured in individuals of different sizes and at different temperatures. Grazing experiment where T. compressa were offered different densities of zooplankton were performed. The material from the grazing and respiratory experiments have been analyzed for dry matter and content of carbon, nitrogen and phosphorus, and it is established length carbon relationships. Individuals of T. libellula and T. compressa will be analyzed for fatty acid composition, which can provide supplementary information about diet. NORWECOM.E2E is an "end to end" ecosystem model that includes a fine scale representation of the physical properties of the ecosystem, biogeochemistry and selected important components of the ecosystem. In NORWECOM.E2E is now krill implemented and can be run simultaneously with copepods. The krill model is also run offline with a time horizon of 80 years to study the life history traits of krill. A model of Calanus hyperboreus has also been implemented in NORWECOM.E2E. It includes full life story of C. hyperboreus based on data from the literature. In the Greenland Sea, the model suggests a lifecycle of 3-4 years from hatching to spawning.

The demand for feed to the aquaculture industry has shown a strong increase over the last years in parallel with the increase in total production within the industry. Estimated growth in the fish farming industry is supposed to cause a permanent shortage of marine oils within a few years, and of marine proteins on a longer time scale. At present traditional marine biological recourses are exploited at the highest possible level. In many seas exploitation is far beyond any sustainable level. Thus, further increase in marine harvest to sustain growth in the aquaculture industry, cannot be based on the marine resources exploited at present. The only unexploited marine resources of significant biomass are found at lower trophic levels, comprised by population s of zooplankton and mesopelagic fish. A fishery on plankton should not be developed without quantitative knowledge about standing stock and production of marine plankton, and the effects of harvesting plankton on the ecosystem in general and on commercia lly harvested fish stocks in particular. The overall goal is to improve abundance estimates and assess stocks of zooplankton to enable quantification of ecological consequences of harvesting at lower trophic levels. Improved methods of abundance estimati on and model driven stock assessment of plankton will form the basis of our approach. With knowledge of plankton population biomass and production at hand, effects of harvesting plankton can be explored by ecosystem models with respect to plankton populat ions themselves, the ecosystem and food requirement for commercial planktivorous fish stocks. The results will be disseminated as advice to managers. The contribution by HARVEST II to quantitative information about distribution, production and ecological role of plankton populations will also form an important knowledge base to the development of ecosystem-based management of fisheries.