3o8 



BENNET B. RAE 



coasts on the Continent, including the Faroe Islands (Hewer, 1955; Hickling, 

 1957). There is, however, as yet no evidence that this movement reaches any- 

 great proportion since continental writers do not record any marked seasonal 

 increase in their seal populations. 



On the other hand, against this argument it may be stated: (i) that the 

 British grey seal population is now almost certainly greater than 20,000 

 estimated by Lockley (1954); (2) that seals are known to kill more fish than 

 they eat and that when they do eat they select choice portions and reject the 

 head, skin and tail fm of large fish such as salmon and cod. The 15 lb offish 

 estimated as being eaten by a grey seal daily must therefore represent a 

 greater weight of fish killed. 



1° W) 



Table I 



Area or locality- 

 Southern North Sea (offshore) 

 Fame Deeps to Berwick coast 

 East of May Island 

 Firth of Forth . 

 Central North Sea (offshore) 

 Aberdeenshire coast (eastwards to 

 Moray Firth 

 Orkney (coastal) 

 Shetland (Balta) 

 Northern North Sea (offshore) 

 North coast of Scotland 

 West of Scotland 

 Inner Firth of Clyde . 



Seals are now known to have another harmful effect on fish stocks by the 

 propagation of the parasitic worm, Porrocaecum decipiens (Krabbe), which 

 appears in its larval form in the muscles of a number of food fishes but 

 particularly in the cod. In this connection the researches of a number of 

 Canadian scientists are well known (Scott & Martin, 1957; Scott & Fisher, 

 1958; Templeman, Squires & Fleming, 1957). On the west coast of this 

 country nematode parasites have been known in cod and other gadoids for 

 many years. Until recently, however, North Sea grounds have been regarded 

 as almost free from this parasite. Following representations from the fish 

 trade this problem has been investigated at Aberdeen during the past three 

 years with rather disturbing results. Preliminary figures are given in Table I. 



Infestation of cod by Porrocaecum decipiens is still either absent or very Hght 

 on all offshore grounds in the North Sea. In coastal waters, however, it 

 varies from less than i per cent off the Aberdeenshire coast to over 20 per 

 cent on the Northumberland and Berwick coasts, round the Orkneys and 

 the Shetlands and to nearly 40 per cent on the west of Scotland, where, 



