Primary production, through photosynthesis, in the form of plankton, is a limiting factor on the size of the biomass further up the food chain. In view of this, it is possible to calculate how great a share of primary production is occupied by marine mammals on the various levels of the food chain. This share will, of course, vary with the size of the stocks. Should we decide to maintain large stocks of marine mammals, while at the same time deciding not to harvest these stocks, then an entire segment of the flow of energy through the food chain will be inaccessible to the fisheries. Such a management system will, in other words, reduce the possible sustainable yield of the marine ecosystems.
Norwegian scientists weigh cod found in the stomach of a minke whale.