EFFECT OF SEAL STOCKS ON SCOTTISH MARINE FISHERIES 307 



be summarized as (i) fish mutilated or killed and eaten; (2) nets torn; (3) 

 interruption of fishing time; and (4) diversion offish from nets. 



The impact of seals on Scottish fisheries is dealt with in more detail 

 elsewhere (Rae, i960), and for the present attention is focused on the effect 

 on marine fisheries. 



So far few complaints regarding seals have come from Scottish sea fisher- 

 men. The reason for this, however, is fairly obvious. Most marine fishermen 

 employ active methods of fishing such as trawling and seining. Most of the 

 damage attributed to seals abroad has been in respect of passive fishing gears, 

 but in Scotland these methods comprise only a small proportion of the total 

 fisheries. Anchored nets and lines on the west of Scotland, however, have 

 suffered from seal activities for a long time but since the war cod-net and 

 small-line fishermen on the coast of Angus have been troubled by seals 

 tearing their nets and eating or mutilating their fish in a manner similar to 

 the damage sustained by salmon fishermen using bag-nets. Although these 

 passive fishing methods form a small part of Scottish fisheries (drift-netting 

 ifor herring fortunately is largely carried on outside coastal waters where seals 

 are active) they are nevertheless essential owing to circumstances in particular 

 localities. 



This form of damage from seals, however, is small in comparison with the 

 damage apparently done to fish stocks as a whole. This aspect of the problem 

 may be considered by a rough calculation of the quantity of fish eaten by 

 seals. Assuming totals of 20,000 grey seals and 18,000 common seals, 

 and accepting estimates of the daily requirements of these animals as 1 5 lb 

 and II lb of fish respectively (Matthews, 1952 and Havinga, 1933), the daily 

 consumption by both species would amount to 220 tons and the yearly total 

 to 80,000 tons. It is not known whether all this fish would be taken in 

 *home' waters (see below) but it is noteworthy that this weight is the 

 equivalent of one-fifth to one-sixth of the total British catch of all species of 

 fish from home waters. 



It has been estimated that 80 per cent of the seal population is based on 

 Scottish waters for feeding purposes, and, assuming that the quantity of fish 

 eaten is in the same proportion, this means that 65,000 tons offish are eaten 

 by seals in Scottish waters every year. This weight is the equivalent of 

 between one-quarter and one-fifth of the total Scottish catch from home 

 waters. It is certainly not suggested that in the absence of seals Scottish 

 landings would be increased by that amount, but it does mean that the 

 catches of Scottish fishermen must be reduced to some extent. 



Objections may reasonably be raised to this view on the grounds that it is 

 not known if all British seals remain in home waters throughout the year. 

 Tagging experiments on grey seals do show that some migrate to different 



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