62 



Appendices to Second Annual Report 



autumn and spring herring. This difference is illustrated by figs. 2 and 

 3, PI. IV., which represent two ripe male spring herring taken at 

 Anstruther. A somewhat different and even more marked variation is 

 seen in figs. 1 and 2, PI. V., which represent two spring herring sent on 

 the 28th March from Girvan, the one a full herring, which weighed 12 

 ounces, and measured 13 inches in length, while the other represents a 

 spent herring of the same length. In the full herring, the dorsal fin is 

 situated further back, and the ventral fin slightly further forward than in 

 the spent herring. 



The same variations occur amongst the autumn herring, so that unless 

 some better distinction than the position of the fins is discovered, it will 

 be difficult to distinguish, by structural characters, a spring from an 

 autumn herring, and the same difficulty is likely to arise in endeavouring 

 to distinguish between a west and an east coast herring. At first it was 

 difficult to account for herring spawning twice a year — in the spring and in 

 the autumn. Some believe that the herring which spawn in March spawn 

 again in September, but this is very unlikely. It is more probable that 

 the shoals which spawned last spring will not spawn again until next 

 spring, and that the shoals which spawned last antumn will spawn again 

 for the first time next autumn. If this is so, how is it possible to account 

 for the appearance of two distinct races of herring ? We may suppose 

 that at first all herring were in the habit of spawning about the same 

 period — it may have been in autumn or in spring — but that as time went on, 

 probably as the result of variations, herring were found spawning during 

 each month of the year. 



As an indication of this, we have had specimens of herring ova sent 

 almost every week from the Aberdeenshire coast during the winter ; this 

 shows that herring have been spawning in one district without interrup- 

 tion for at least ten months — from August 1883 to June 1884. 



Granting that herring spawn all the year round, we can, I think, easily 

 understand why at the present day there are two great spawning periods 

 every year. The explanation is not, as has generally been supposed, that 

 spring and autumn are the best seasons for the depositing and hatching of 

 the eggs, but rather that spring and autumn are the two most favourable 

 periods for the appearance of the fry. During my first visit to the 

 Ballantrae Bank in March, I w r as struck by the almost complete absence 

 of surface forms, while I was equally impressed during my second visit a 

 fortnight later with their immense numbers. Now the number of indi- 

 viduals of any given species does not depend so much on the number of 

 eggs formed as (1) on the number of eggs successfully batched, and (2) 

 on the number of fry that survive. In the case of the herring the 

 number seems chiefly to depend on the survival of the fry. This conclu- 

 sion has been arrived at because nearly all of the many millions of eggs I 

 have dredged had been fertilised — generally they contained active em- 

 bryos — and because the fry when hatched are at first effectively protected 

 by their minute size and great transparency ; hence given sufficient food, 

 they are likely to pass safely through the larval stages at least. If in 

 spring and autumn this larval food is more abundant than at other times, 

 it will be evident that in course of time more fry would survive in spring 

 and autumn than during any other months, and this continuing generation 

 after generation, enormous shoals of spring and autumn herring would be 

 formed. 



II. 



THE MIGEATION OF THE HERRING. 



More has probably been written on the migration of the herring than 

 on any other fish problem, but, as a matter of fact, we, at the present 



