Herring as a major consumer in the Norwegian Sea

Using available information, the authors attempt to calculate the food consumption of the Norwegian Spring Spawning Herring in the Norwegian Sea in the years 1994-1996, and to calculate how much is taken of different prey organisms. Consumption/biomass ratios extracted from literature vary within the range 3.0-7.0. Based on the likely size of the herring stock in the Norwegian Sea and an annual consumption/biomass ratio of 4.5, the consumption in 1994, 1995, and 1996 was calculated to be 31, 40, and 47 million tonnes, respectively. Quantitative data are presented on the presence of different prey categories in herring stomachs in different water masses (Coastal, Coastal/Atlantic, Atlantic, and Atlantic/Arctic, respectively), and the results are used to estimate total consumption of the different prey categories by herring. Based on a consumption/biomass ratio of 4.5, the consumption of copepods in 1994, 1995, and 1996 was calculated to be 19, 24, and 29 million tonnes, respectively, making up 62% of the food consumed as a mean over the 3 years. Corresponding numbers for krill were 1.2, 3.3, and 1.8 million tonnes and 5%, and for amphipods 3.3, 5.2, and 6.6 million tonnes and 13%. The results are compared with the assumed production by the different prey organisms in the areas where the herring feed. For copepods it seems that the consumption by herring is at the same level as the production, but for other prey organisms the production seems to exceed consumption by herring. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.