Growth, feeding, production, and consumption in 0-group bib ( Trisopterus luscus L.) and whiting ( Merlangius merlangus L.) in a shallow coastal area of the south-west Netherlands

Abstract

In 1988 juvenile bib ( Trisopterus luscus ) and whiting ( Merlangius merlangus ) were studied in a shallow coastal area by monthly sampling with fine-meshed nets. 0-group fish of both species are first caught in May. By the end of the first growth season bib reached about 150 mm SL (standard length), whiting about 170 mm SL. Maximal densities were recorded in June and by the end of the year most fish had left the area. The instantaneous mortality is estimated at 0.008 day ⁻¹ (0.77% day ⁻¹ for bib and 0.76% day ⁻¹ for whiting) for both species. In May both species depended almost exclusively on calanoid copepods. In June and July mysids and amphipods were the most important invertebrate prey, but small fishes such as gobies provided a substantial proportion of the energy requirements, especially in whiting. From August onwards shrimp and fish dominated the diet in both species. Using Jones' (1974) model, food consumption as per cent body weight day ⁻¹ varied between 4 and 6% during summer the declined to 2 to 3% in autumn. Total consumption per unit area of subtidal seafloor, by the 0-group fish of both species taken together, was estimated at 0.47 g ash-free dry weight (ADW) m ⁻² year ⁻¹ using Jones' (1974) model and at 0.57 g ADW m ⁻² year ^-1 using a conversion efficiency (P:C ratio) of 0.34.