On the Association of Jelly-Fish and Other Organisms with Catches of Herring

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Abstract
Investigations into the relations between plankton and herring, using the Hardy Plankton Indicator, were carried out by this department during the years 1930 to 1933 (Hardy, Henderson, Lucas and Fraser, 1936). In planning this work Professor Hardy made provision for obtaininginformation, when possible, on weather conditions and on the occurrence of organisms which would not be caught in the plankton samples. Information on the presence of jelly-fish, was specifically requested. Skippers of drifters using the Indicator were asked to fill in a printed labelfor each disc giving details of ship, date, time, position and catch, and the following sentence was printed at the foot of the label:— “ Any further notes regarding state ofweather, sea, presence of jelly-fish, or any unusual conditions may be written on the back.” Since the details of date, position, catch, etc., were essential for the success of the Indicator experiments, only these were definitely asked for, and skippers were left to supply further information if they had time to do so. Much more exact and extensive information regarding the presence of jelly-fish arid other organisms could have been obtained if the enquiry had been confined to these points, and it is hoped that this may be done in the future, either from thisdepartment or by other workers. Russell (1935, b), in stressing the importance of plankton organisms as indicators of different hydrological conditions, says “it is especially valuableto watch for any correlations between the presence or absence of certain plankton animals with that of fish and larger swimming animals.”

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