An attempt to estimate the predatory pressure exerted by the lesser weever, Trachinus vipera Cuvier, in the southern North Sea

Abstract

In order to evaluate the impact of the lesser weever on the ecosystem of the southern North Sea, geographical distribution, density, growth, production and food requirements have been estimated. High densities were found on and around the Brown Ridge, an area with high tidal current velocities, medium grain‐size of the sediment and a poor benthic fauna. Growth is restricted to the months of June October. During the winter cessation of growth a considerable loss of weight (about 20%) takes place. Mortality has been estimated by using the average size frequency distribution of all catches made from 1972 to 1984. The resulting convex type of survival curve indicates a high survival rate of the II to IV‐group fishes. The production (estimated with Allen's graphical method) of a population of 100 individuals including all age groups (0‐VI) amounts to 123.7 g AFDW‐year‘. In areas with highest densities, consequently, production amounts to 0.018–0.078 g AFDW‐m2 ‐year‐1. With an assumed transfer efficiency of 10% through the year, food requirements amounts to 0.18–0.78 g AFDW‐m 2 ‐year ‐1. Since the lesser weever feeds mainly on fish (85.6%), almost exclusively on gobies (Pomatoschistus sp.), and with an assumed transfer efficiency of approximately 10%, the indirect predatory pressure exerted by it may amount to 1.6 6.7g AFDW‐m 2.year ‐1. A possible feeding by gobies on pelagic organisms (calanoids, mysids) is discussed.