RELATIONSHIP WITH FISHERIES 



summer. Although herring will take other foods when necessary they prefer 

 Calamis if available in sutiicient quantity. In the colder waters such as the 

 Barents Sea, Calaiiiis forms about 80 per cent of the total weight of all zoo- 

 plankton species together. When Calamis feeds on the living diatoms etc. 

 in the phytoplankton near the surface they are rather pale in colour, but if 

 they feed largely on distintegrating material, as they must do in deeper 

 water, they are red and very oily. The herring feeding on Calamis are cor- 

 respondingly oily and if there is too much oil the herring can be too rich 

 for proper curing. Hence too rich a food supply is not necessarily a good thing 

 for the market. Herring when full of Calamis have what is called 'red gut' 

 and as a rule are in excellent condition. If they feed on the small mollusc 

 Spiratella with its black shell and strong smell they have 'black gut' and do 

 not keep so well nor fetch so good a price on the market. 



l{ Calamis is such an important part of herring food could one assume that 

 herring would be more abundant where this kind of food is? If so would it 

 then be possible to increase the catch by fishing only in areas where a plankton 

 sample showed that Calamis was common? In 1932 this experiment was 

 tried on the North Sea herring grounds. Fishermen co-operating in the 

 experiments towed a 'Hardy' Plankton Indicator (Fig. 5) for a mile before 

 shooting their nets and the plankton was analysed and associated with the 

 resultant catch. By and large the experiment worked, not always but on the 

 average, as shown in the table and in Fig. 34. For example, when Calamis 



In poorer Calamis water In richer Calamis water 



was below the average of the sample the average catch was fourteen and a 

 quarter crans; against thirty one and a half crans i{ Calamis was above average. 



131 



