OF DIATOMS AND COPEPODA IN THE IRISH SEA. ll5 



from the yacht at various localities in the deep locha on the west coast of 

 Scotland large hauls of Calanus by means of vertical hauls when no 

 specimens were obtained at the surface. In fact this Copepod seems to be 

 permanently present in the deeper waters of these lochs. 



Tn addition to these deep water specimens of Calanus we find on occasions, 

 on the west coast of Scotland, large swarms on the surface, which may be 

 the result of invasions from the ocean, and there is a considerable amount of 

 evidence that such swarms are the cause of local mackerel fisheries. 



Some years ago (1909) Dr. E. J. Allen and Mr. G. E. Bullen published* 

 some interesting work, from the Plymouth Marine Laboratory, demonstrating 

 the connection between mackerel and Calanus and sunshine in the English 

 Channel ; and Farran f states that in the spring fishery on the West of 

 Ireland the food of the mackerel is mainly composed of Calanus. In the 

 summer of 1913 we had an experience at Tobermory, in Mull, which I shall 

 quote from two letters written from the yacht at the time, and published in 



' Nature.' 



"S.Y. 'Runa,' Tobermory, July 12th, 1913. 



" On arriving in this bay last night we found that the local boats had been 

 catching abundance of mackerel close to. We bought some for supper (good 

 fish for a halfpenny each), and on dissection found that the stomachs of all 

 of them were crammed full of fresh-looking Calanus (the individual Copepods 

 being for the most part distinct and perfect), along with a few immature 

 Nyctiphanes and larval Decapods. Professor Newstead and my daughter 

 then noticed, while fishing over the side of the yacht, about 8 p.m., that the 

 gulls in the bay were feeding in groups around patches of agitated water 

 evidently caused by shoals of fish. On rowing out to these we saw distinctly 

 the mackerel, large and small, darting about in great numbers in the clear 

 water, and we also noticed every here and there on the smooth surface of the 

 water — it was a beautifully calm evening — innumerable small whirls or 

 circular marks which, looking closely, 1 1 found to be caused by large Copepoda 

 close to the surface. 



" About twenty years ago I sent a note to ' Nature,' from the yacht ' Argo,' 

 in regard to large Copepoda (I think it was Anomalocera on that occasion, and 

 the locality was further north, off Skye), splashing on the surface so as to 

 give the appearance of fine rain ; and this present occurrence at once 

 reminded me of the former occasion, but here the Copepod was Calanus 

 finmarchicus of large size and in extraordinary abundance. They could be 

 clearly seen with the eye on leaning over the side of the boat, a small glass 

 collecting jar dipped at random into the water brought out twenty to thirty 

 specimens at each dip, and a coarse grit-gauze tow-net of about 30 cm. in 

 diameter caught about 20 cubic centimetres of the Copepoda in five minutes. 



* Journ. Mar. Biol. Assoc, vol. viii. (1909) pp. 394-406. 



f Couseil Internat. Bull. Trimestr. 1902-8, Planktonique, p. 89. 



