The Seasonal Distribution of Macroplankton as shown by Catches in the 2-metre Stramin Ring-trawl in Off-shore Waters off Plymouth

Abstract

In past years during the study of the vertical distribution of macroplankton much information has been obtained on the abundance of the different animals in the catches at different times of the year. Results have already been published to show the seasonal distribution of pelagic young fish (4), and also on the abundance and composition of the Sagitta population (5, p. 565). In this latter study the change over from the predominance of Sagitta clcgans to that of S. sctosa during the years 1930 to 1932 is striking. During the examination of catches it has been noticed that each year has been characterised at some time by the abundance of a species which may occur only in small numbers, if at all, in other years. This has been especially noticeable in the composition of the medusa population. It is necessary to follow these changes through a number of years to see if the presence of certain plankton organisms cannot be used as an index of conditions that may lead to other fluctuations such as those of the fisheries.