Occurrence of eelAnguilla anguilla larvae west of the European continental shelf, 1971–1977

Synopsis

Seven hundred and thirty seven eel larvae were caught in 1971 and in the period 1973–1977 by a modified Isaacs Kidd Midwater Trawl off and on the continental shelf west of France and the British Isles. According to Schmidt (1909) no larvae have been caught on the shelf itself except one glass eel. A decrease in number as well as a decrease of older stages from east to west was observed. Besides the maximum in the length frequency distribution some more smaller peaks occurred. No essential size differences existed between 1975 and 1977, between younger and older developmental stages and between northern and southern larvae. Depth preference during daylight was 300–600 m, at night 35–125 m. Mean density of larvae in the preferred depth layers was nearly 1 per 1000 m³. High densities alternated from year to year with low densities which corresponded to the total catch fluctuations of the elver ascent in the River Ems at Herbrum (West Germany) in the following spring. The possible relationships in mortality between the metamorphosing leptocephalus and immigrating elvers and between the emigrating silver eels and the metamorphosing leptocephalus are discussed.