0 



of the Fishery Board for Scotland. 47 



salinity been favourable for the incursion of Salps. In other words, 

 the presence of Salps within the Scottish area of the North Sea is an 

 indication of unusual hydrographic conditions. 



With regard to the magnitude of the invasions of the Salps in 

 1920 and 1921, it may be stated that they could easily be seen in 

 numbers, from the deck of the ship, floating passively in the water, 

 and hauls at all depths with a net, the mouth of which was only one 

 yard in diameter, yielded enormous numbers. Indeed, in the main 

 line of the invasion the area was flooded by these forms almost to 

 the entire exclusion of all other forms, and there was a marked 

 absence of the normal crustacean fauna on which herring very largely 

 feed, a fact which may account for the reported poor condition of the 

 herrings caught in the drift-nets. 



While it cannot be asserted that the poor results of the fishing in 

 1920 and 1921 were due entirely to the abnormal hydrographic 

 conditions, it is significant that the area invaded by the Salps 

 coincided very closely with that usually fished by the drifter fleet. It 

 will also be noted that in 1921 the successful operations of the 

 trawler fleet fishing for herrings were conducted beyond the boundary 

 of the Salp-invaded area where the cooled down Atlantic water of the 

 previous year had not then been displaced by the invading water 

 masses. The position of the trawler fleet, includicg a large number 

 of German boats, is indicated on the chart by a dotted area. The 

 temperature of the bottom water to the eastward of the broken line 

 on the chart was everywhere less than 8° C. (46° F.), and to the west- 

 ward of the line, within the invaded area, greater than 9° C. (48° F.). 



In order to carry out an investigation on the younger stages of 

 the herring, the motor boat " Enid," with two naturalists on board, 

 was stationed at Inverness Firth early in December. A systematic 

 examination of all classes of herring from the areas of the Inverness 

 Firth and Beauly basin was commenced and continued throughout 

 the winter. Attention was also given to the very young stages, about 

 which a great deal is still unknown. The very small herrings are ex- 

 tremely difficult to catch, and experiments are being made with various 

 types of nets and gear with the object of facilitating their capture. 



4. Haddock. 



By agreement with the Ministry of Agriculture and Fisheries, it 

 has been arranged that the Board shall be entirely responsible for 

 the share of the United Kingdom in the international investigations 

 on the haddock, and the English department for the investigations on 

 the cod. Material is, therefore, exchanged in conformity with this 

 arrangement. 



Large fluctuations in the stock of small haddocks from year to 

 year are a characteristic phenomenon in this particular branch of the 

 fisheries, and the year 1921 was, as in 1906, marked by a great 

 abundance of small fish. 



The trawling investigations carried out by the research vessel 

 included the capture of a very large number of haddocks, all of which 

 were measured, and definite information was obtained as to the size 

 frequencies of fish caught on the inshore grounds by an otter trawl. 

 These catches are directly comparable with those of the inshore 



