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Plankton Studies in Relation to the Western 

 Mackerel Fishery. 



By 

 G. E. BuUen. 



With Six Charts (Plates XVIII-XXIII), two Figures in the Text and Tables I-V. 



I. METHODS. 



The researches here described extended for intermittent periods over 

 the years 1906 and 1907, and were primarily intended to embrace 

 inquiry into the food problem of Pilchard, Herring, and Mackerel 

 frequenting the western part of the English Channel. The observa- 

 tions now recorded form, therefore, a part of a wider series. 



Most of the information referring to the condition of the fishery 

 throughout the spring season of the two years was collected at 

 Newlyn and Plymouth, by systematic inquiry amongst the fishermen. 

 Other information was derived from the market reports of the Fish 

 Trades Gazette and other journals, and from Mr. Mathias Dunn of 

 Newlyn, who kept the fishery constantly under observation. 



The samples of plankton and stomach material were obtained from 

 various sources. Some were taken by myself at sea from fishing-boats 

 or from the Oithona, others by fishermen ; whilst a good deal of the 

 stomach material was got from systematic collections made at Ply- 

 mouth and Newlyn from catches landed at those ports. In addition 

 to the plankton samples mentioned above, certain samples taken at 

 the western stations during the international cruises were also ex- 

 amined and the results utilized. 



The plankton was collected for the most part by a compound tow- 

 net embodying in its construction Swiss bolting silk of two sizes of 

 mesh, viz. («) 18 holes per 1 cm., the average length of a hole being 

 •056 cm. and the average breadth being 'OSe cm., and (l) 70 holes per 

 1 cm. The surface hauls were usually made for ten minutes. The 

 contents of the net were filtered through a net-bag constructed of the 

 fine silk mentioned above, and the product preserved in 5 % formalin. 



NEW SERIES. — VOL. VIII. NO. 3. OCTOBER, 1908. T 



