

SEA-FISHERIES LABORATORY. 107 



FOOD OF PORT ERIN MACKEREL IN 1919. 

 By A. Scott, A.L.S. 



The mackerel fishery off Port Erin appeared to be much 

 later in 1919 than in some previous years. It was not till the 

 end of the first week of August that the fish were caught in 

 any numbers. Professor Herdman, who was collecting- 

 plankton for the " Intensive Study " investigation, wrote me 

 on August 8th as follows : — " Since the late phyto-plankton 

 passed of! the copepoda have been increasing, and on August 

 6th I got a rich copepod haul off Bradda Head and at once 

 put out two mackerel fines and went back over the same 

 ground, where a gannet was fishing. In a few minutes I caught 

 fourteen mackerel. I opened them and took out the stomachs 

 and found them crammed full of copepoda. I am sending a 

 tube containing the contents of the stomachs of six mackerel. 

 You might see how many species you can determine and how 

 the results agree with the tow-net hauls." 



The stomach contents were carefully washed out into a 

 black photographic developing dish and examined with the 

 pocket-lens to get a general idea of the constituents. Pieces 

 of stomach wall were taken out and conspicuous organisms 

 such as zoea and megalopa and the larger copepoda were 

 counted individually and also removed. The residue was then 

 well mixed with water, transferred to a measuring cylinder and 

 allowed to stand till the volume became constant. It was 

 read ofT and amounted to ten cubic centimetres. The 

 organisms were afterwards estimated in the manner adopted 

 in the examination of the plankton catches. The result is 

 given in the first column below. The second column gives the 

 mean number per fish of each organism in whole figures, 

 with the exception of Anomalocera. 



