56 



Thirty -ninth Annual Report 



graphical conditions a similar incursion took place. During the 

 course of the cruise these salps were found in all waters from 

 Kinnaird Head northwards to beyond Shetland, embracing the 

 greater part of the area within which the summer herring fishing is 

 carried on, and their abundance may be judged from the fact that 

 herring fishermen frequently found that the drift nets were clogged 

 with them and could be hauled only with difficulty. 



Another striking feature, revealed by the collections made by 

 pelagic nets, was the remarkable dearth of the ordinary minute 

 Crustacea which are usually found in these waters at this period of 

 the year and which constitute the principal food of the herring. It 

 would appear as if the salps had flooded the area to the exclusion of 

 all other forms of marine life. 



Whether the lack of success experienced by the drift net fishermen 

 was due to the abnormal conditions thus revealed it is difficult to say, 

 but further attention is being given to the point. It may be noted 

 that in 1905 when the last incursion of salps took place herrings 

 appear to have been almost entirely absent from the Moray Firth 

 grounds, but were taken in abundance on the grounds from 50 to 60 

 miles east of the Shetlands throughout the season. 



Attention was also directed in the course of the cruise to dog fish, 

 which are frequently a pest in Shetland waters. The absence of the 

 smaller forms and the rarity of gravid females lent support to the 

 view already held that the species really belongs to the warmer waters 

 of the Atlantic, from which it makes incursions of longer or shorter 

 duration into the North Sea. 



Experiments were made off the Shetland coast with anchored 

 herring nets of various sizes of mesh. The following four distinct 

 groups of herrings were found to be present : — 



1. Length approximately 5 inches ; not well represented in 



catches, but evidently abundant. 



2. Length 7 J— 8 inches ; very fat, reproductive organs still imma- 



ture ; well represented. The local fishermen were unaware 

 of the presence of this group, as the mesh of the anchored 

 nets they were using was too large for their capture. 



3. Length approximately 9 \ inches ; fat ; reproductive organs in 



some cases beginning to develop. 



4. Length 10-12J inches ; not homogeneous as regards sexual 



development, both spent and maturing fish being present. 



From the records it may be provisionally deduced that the herrings 

 approach the coast in the first year of their life and remain in the 

 neighbourhood for at least two years. 



An investigation was also made during the year as to the con- 

 dition of trawled herrings from various localities in the North Sea, 

 especially in relation to the development of the reproductive organs 

 and the nature of the food contained in the stomachs. 



A research was also instituted on larval and post-larval herrings, 

 and on the distribution of the small herrings in inshore waters. 



It may be mentioned in relation to the growth of the herring that 

 in August 1917 certain small herrings procured in the estuary of the 

 Dee were put in the large spawning pond, the fish measuring approxi- 



