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Trophic levels of basic food items, feeding habits and trophic levels of various North Sea fishes have been derived from historical references and the MAFF North Sea Groundfish Survey data in 1977, 1978 and 1980. There is an obvious progression in the mean trophic levels from planktophagic (3.5) to benthophagic (3.9) and ichthyophagic (4.5). The mean trophic level of 34 species for the period 1947-77 is 3.67. While the total catch and the catch of some species were fluctuating widely, the mean trophic level of the nominal catch of fish (excluding several less important species) showed almost no changes (3.62-3.76) from 1947 to 1977. Generally speaking, the catch should approximately reflect the abundance in a well exploited sea. Assuming that the trophic levels of 34 species were similar during 1947-77, fishing does not appear to have upset the fundamental ecological balance of the North Sea. In other words, the influence of fishing has not yet surpassed the self-regulatory capacity of the North Sea ecosystem.

A Tentative Analysis of the Trophic Levels of North Sea Fish