Food, Growth and Biological Production of the European Eel, Anguilla anguilla, in a Small Stream in Jutland, Denmark

Yellow eels were sampled by electrofishing in 1979, 1980, and 1981 in Vester Vedsted Stream, Denmark, which has as its outlet to the North Sea. Yellow eels were aged by burning the otoliths. The gender of the eels was not specified, and they varied from 6.5 to 48.5 cm in length. The ages varied from 0+ to 10+ years. The annual growth rate Δ varied from 3.4 cm for the youngest eels to 2.2 cm for eels over 10 years old, with a mean of 3.1 cm. Body mass wet weight was correlated to energy content (kcal), with an annual mean growth rate Δ of 5.33 kcal. In contrast to body length, the annual growth rate Δ of energy content (kcal) increased with age. Von Bertalanffy growth trajectory (cm) of length-at-age was calculated, and L∞ = 118.4 cm. Annual natural mortality M was calculated, and M was significantly dependent on body mass, i.e., high M at low body mass vs. low M at high body mass. The biological production was calculated to be 13.5 g wet weight m−2 per year. A total of 780 eel stomachs were analyzed, 287 (37%) of which were empty. Mass (wet weight, g) of food content increased more than proportionally with eel body mass. Chironomid larvae, Ephemeroptera nymphs, Simulium larvae, and Gammarus pulex were the dominant food taxa, followed by Trichoptera larvae. The size of Chironomid larvae, Ephemeroptera nymphs, and Simulium larvae prey was independent of the length of the eel, whereas the size of Gammarus pulex increased with increased eel length.