|On selective tidal transport in the migration of North Sea plaice (Pleuronectes platessa) and other flatfish species|
de Veen, J.F. (1978). On selective tidal transport in the migration of North Sea plaice (Pleuronectes platessa) and other flatfish species. Neth. J. Sea Res. 12(2): 115-147
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
Evidence is given for selective tidal transport in North Sea plaice and other flatfish species. Data collected during midwater plankton surveys in two Dutch Wadden Sea inlets in early spring in the years 1970 to 1977 show that plaice, sole, flounder and dab demonstrate pelagic swimming behaviour in that period. Plaice, sole and flounder show a clear selective tidal transport mechanism to re-enter the Wadden Sea after staying in the open sea in winter whereas dab tends to leave the Wadden Sea. Data on by-catches of semi-pelagic pair trawl fishery for gadoids in the Dutch coastal area show that small quantities of plaice may be caught off the bottom throughout the whole year whereas sole moves to higher levels in two distinct periods only . The first period coincides with the re-entering of soles in the Wadden Sea and with the well-known phenomenon of soles swimming at the surface. During this period the soles use selective tidal transport to reach the spawning grounds near the continental coasts. Data on catch per unit effort of a Dutch otter trawler in 1958 to 1960, constantly fishing in one restricted area near Terschellingerbank lightvessel, reveal significant differences between day and night catch rates and a change from a preference for flood tide in the first half of the year to a preference for ebb tide in the second half. The available evidence for selective tidal transport in plaice is discussed in relation to the patterns of migration in 4 plaice sub-stocks studied by means of tagging experiments, and in relation to results of displacement experiments with mature and immature plaice. The tagging and displacement experiments present a picture of migration in which the directional swimming is a weak component superimposed on largely random movements and the speeds of travelling are low. The plaice react to displacement by trying to return to their original grounds and this tendency to home lasts for a full year. This picture about selective tidal transport contrasts with results obtained by the Lowestoft Laboratory. Plaice equiped with transponding acoustic tags did show largely directed and fast tidal migration before and after spawning. Arguments are given that these plaice were, however, in an exceptional position and may have shown homing behaviour. Notwithstanding this reservation to the Lowestoft experiments, these results and the present ones are explained if it is assumed that apparently only a fraction of the population uses the mechanism of selective tidal migration, thus saving energy and achieving quick transport when necessary. It is likely that in plaice as in sole the mechanism will be used in special cases only, probably for short periods, in certain areas.