OF DIATOMS AND COPEPODA IN THE IRISH SEA. 



97 



in diameter at the mouth, and are in our weekly gatherings throughout the 

 3 r ear hauled through a definite course in the open water of Port Erin bay. 

 The two together ("coarse'" and "fine" nets) constitute a "standard haul.-" 

 The gatherings taken outside the bay during the periods of the vernal and 

 autumnal plankton maxima were made with the same nets as in the bay, at 

 fixed "stations" respectively three and five (and on a few occasions ten) 

 miles from land *. 



In addition to these standard hauls many others were taken with special 

 nets, such as the closing " Petersen-Hensen " and " Nansen," the "shear- 

 net" and "funnel-nets," usually at depths of 5 to 30 fathoms, and on occasions 

 down to 60 fathoms out in the deep central valley between the Isle of Man 



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25 









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— — 



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Apt. 



Ju*E 



Auct 



Sep 



Oct 



Nov 



Dtc 



Fig. 2. — Typical Irish Sea plankton curves for the years 1913 (dotted line) 

 and 1914 (whole line). 



and Ireland. Figure 1 gives a general view of the various nets used on one 

 of our plankton cruises. Temperatures, surface and deeper, weather observa- 

 tions and water-samples were also taken systematically f. 



The plankton gatherings when taken are at once treated with formol to 

 kill and fix the organisms and prevent further changes. They are then 

 placed (at the Port Erin Biological Station) in graduated cylinders, and 

 after some hours, when the material has fallen to the bottom and the super- 

 jacent fluid is clear, the quantity of plankton in cubic centimetres is 

 recorded. The fixed plankton is then concentrated and preserved in 



* Determined by cross-hearings, and hy distance run calculated from the engines. 



t For further particulars as to methods, see the earlier reports published by the Lanca- 

 shire and Western Sea- Fisheries Committee. 



