Publication Abstract

Changes in the demersal fish assemblages of British coastal waters during the 20th Century

S.I. Rogers and J.R. Ellis

Catches of demersal fish from research vessel surveys in three areas around the British Isles from 1901 to 1907 were compared with survey catches in the same areas from 1989 to 1997. Mesh size, and other characteristics ofthe trawls used, suggested that some ofthese data were comparable and could be used to describe changes in demersal fish assemblages over the last 80 years. In Start Bay (NW English Channel) and the Irish Sea, species diversity was the same in both periods, although the most abundant species in each period were not the same. In English coastal regions ofthe southern North Sea fish populations became more diverse, as plaicePleuronectesplatessa and whitingMerlangius merlangus became less abundant, and the relative abundance of several non-target species such as dragonet Callionymus spp., bib Trisopterus luscus, and bull-rout Myoxocephalus scorpius increased. The proportion in the catch of small fish species (maximum body length < 3 0 cm), which would be least vulnerable to capture by commercial trawls, increased between the two survey periods in Start Bay and the southern North Sea. None ofthese small species were commercially exploited. The proportions of larger teleosts (maximum body length >30cm) in catches decreased in all regions during the time period, except in the Irish Sea where plaice replaced grey gurnardEutriglagumardus as a dominant species. There was a decline in abundance of large sharks, skates and rays including the common skate, Raja batis, white skate R. alba and the angel shark Squatina squatina. During historic surveys, 60% ofthe elasmobranch fauna consisted ofthomback rayRaja clavata, whereas in contemporary surveys, the lesser spotted dogfish Scyliorhinus canicula was the most abundant elasmobranch. Changes in lengthfrequency distribution offish in both target and non-target categories, and other observed changes, were thought to be a response to similar observations recorded elsewhere.

Reference:

S.I. Rogers and J.R. Ellis, 2000. Changes in the demersal fish assemblages of British coastal waters during the 20th Century. ICES Journal of Marine Science, 57(4): 866-881.