Studies of the food of seals on Scottish coasts were continued at the Marine Laboratory from 1967 to 1971. In general the results confirmed those of 1958–66 in stressing the supreme importance of fish, particularly species of economic value, in the food of both the Grey and Common seals. Four families of fish–salmonids, gadoids, clupeoids and pleuronectids– were again prominent in the food of both species of seal although the frequencies with which they appeared in the stomachs varied from one period to another. Grey seals preyed more heavily on salmonids and gadoids and Common seals on gadoids and clupeoids. Changes in the diet of seals from one year to another would appear to arise from the sampling of the seals for examination and to the availability of the species offish preyed upon, depending on seasonal movements and natural fluctuations in their age–groups.
Investigation of the food (through stomach contents) of Common porpoises caught in Scottish waters, discussed in an earlier paper, has been continued at the Marine Laboratory. The results confirm the earlier conclusions and stress the prominence of fish in the food. They also indicate the comparatively small size of the fish eaten and the predominantly pelagic or semi‐pelagic nature of the majority of species in the diet.
Dead and dying fish were reported from the Moray Firth during a period of 15 days in September 1963. The initial mortalities were in the inner Firth, but they later spread outwards, especially eastwards along the southern shores of the Firth. Mass mortalities of the lugworm (Arenicola marina) also occurred in Scottish waters in 1962 and 1963, and at Balintorein Easter Ross fish and lugworm mortalities were contemporary.
The stomach contents of porpoises from Scottish waters were examined primarily to ascertain if these animals prey on salmon. The dominant fish in the food were clupeoids and gadoids with herring and whiting the commonest individual species. The food types were predominantly pelagic in habit and most of the fish eaten appeared to be less than 25 cm in length. No evidence of salmon was found in the stomachs and from a study of the jaws and dentition of the common porpoise it seems unlikely that the animal is able to eat any fish as large as a salmon.
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