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Migration of Crangon crangon in surface waters near the "Texel" lightship
Van Der Baan, S.M. (1975). Migration of Crangon crangon in surface waters near the "Texel" lightship. Neth. J. Sea Res. 9(3-4): 287-296
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, meer
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| Abstract |
It was found that in surface waters around the "Texel" lightvessel Crangon crangon (L.) was present in small numbers every winter between about November and mid-May. Superposed on this fairly regular occurrence there were a number of peaks, always occurring in the same order of sequence. In the first two winters of the research (1961-1962 and 1962-1963) a period of maximum occurrence in ebb-hauls in early winter was followed, after an interval of small catches, by a series of flood peaks in spring. In the following, milder winters the ebb peaks in winter were always preceded by a series of flood peaks, so that in these winters the sequence was: flood peaks, ebb peaks, flood peaks, not counting the intervals of smaller catches. Though the observations with only ebb peaks are not inconsistent with the hypothesis of passive migration with the help of tidal currents, those with flood peaks and subsequent ebb peaks cannot be explained in this way. Therefore, it is argued that the peaks may represent concentrations of shrimps keeping together in the same area. The current pattern around the Texel lightvessel (DIETRICH, 1953) offers a more likely explanation, namely of a transport component perpendicular to the coast line. At first shrimps would concentrate in an area not far off the coast and later in winter in an area more towards the open sea. In early spring, when the temperature of the Wadden Sea approaches that of the open sea, they concentrate again at the coastal side of the lightvessel. They disappear from the catches at the time that the temperature of the Wadden Sea surpasses that of the open sea. |
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