NATURE ADRIFT 



will become choked. The larger the mesh the greater the loss of the smaller 

 organisms through the net. Because plankton has such a range of sizes there 

 is no ideal size of mesh ; cither we use a fme mesh in an attempt to capture 

 a large proportion of the plankton present in a small volume of water, or 

 we use a coarser mesh and catch only the larger animals from a larger 

 volume of water. 



If we use a centrifuge instead of a net the same principle applies, we 

 can either extract only the larger organisms from a relatively short or slow 

 spin or we can extract also the smaller ones using a longer or a faster spin. 



The next problem is that of dealing with the immense quantities of 

 water, and this is a double problem, one of handling the water and one of 

 supplying the necessary power, using either nets or a centrifuge. The cost 

 of the power must be deducted from the returns and unless free power is 

 available this is a very serious item. Free power could be available in tidal 

 estuaries — where there is usually more silt than plankton — or in certain 

 places round the coast where there is a strong tidal run. These places do not, 

 as a rule, have a reliable plankton content; sometimes it will be moderately 

 rich, at others very poor, or made up of comb-jellies and other unwanted 

 species. The richest and most reliable sources are those of the cold waters 

 of the Arctic and Antarctic, miles from the places where plankton is most 

 wanted, and miles away from laid-on power supplies. 



This leads us to the next difficulty, one of preservation. Once it is caught 

 plankton will not keep long, and the time will depend on temperature. In 

 the tropics it would be rancid or putrid within a hour or so, and it cannot 

 be stored in quantity in ice in a fish hold to keep during transit from the 

 Arctic as can individually handled fish. Plankton would need to be deep 

 frozen, or much more preferably, dried on the spot using the same type of 

 machinery that is used to produce dried milk. The apparatus, the power to 

 work it, the personnel to use and maintain it, must all be on the spot, again 

 adding to the production costs. 



Towing a plankton net for a biological sample is all right, but it is 

 not feasible merely to increase the size of the net to give a larger sample. 

 Fine-meshed netting offers a big resistance to the water, it is delicate and 

 easily torn by sudden surges due to waves or the ship's motion, so that a 

 very large net is not a practicability and it would be impossible to handle 

 large fine nets from a ship, or in a tideway, especially in bad weather — and it 

 will often be bad weather where the plankton is richest ! 



Perhaps the most efficient method would be to build an artificial whale 

 or basking shark in the form of a ship with an 'open mouth' below the 

 surface— so as to avoid all floating debris such as timber, straw, seaweeds, 

 bottles, feathers etc. This open mouth would lead to revolving fine-meshed 



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