42 Part III. — Tioenty -sixth Annual Report 



The fluctuations in the numbers from one year to another were owing, 

 as a rule, to the variation in the stock of the adult spawning fishes in the 

 pond ; the decline in the last two years was caused by the stock being 

 very small, the usual method of obtaining supplies by the use of a 

 trawler in the Moray Firth and Aberdeen Bay having been given up for 

 reasons explained elsewhere.* 



Besides plaice, other food fishes were dealt with in some years, the 

 following numbers of the fry being liberated : — Cod, 4,010,000 ; turbot, 

 5,160,000; lemon dab, 5,725,000; haddock, whiting, &c., 2,000,000. 

 In addition to fish, in some years considerable numbers of the larvps of 

 lobsters and of the edible crab were hatched and placed in the water along 

 the Aberdeenshire coast. 



It has to be added that the expense of the hatching work is compara- 

 tively small, since the hatchery is operated in conjunction with the 

 Laboratory, the additional outlay for coals, food for the fishes, &c., being 

 estimated at between £60 and .£100 per annum. 



3. The Principles of Sha-Fish Hatching. 



The theoretical objections which are usually made against the artificial 

 propagation of sea fishes for economic reasons are based upon consideration 

 of the vast area of the sea, compared with lakes and rivers, and upon the 

 great fecundity of most sea fishes, especially those which have pelagic 

 eggs. But though the extent of tlie sea is vast, the parts frequented by 

 the food fishes — the fishing grounds on which the fish are caught — are 

 relatively small, and are usually confined to the neighbourhood of coasts, 

 or to banks situated in propinquity to them. Moreover, though the 

 range of wandering of the individuals of many species in relation to the 

 part of the coast where they are born or bred is not well known, we do 

 know that, with regard to plaice at all events, in the earlier years of their 

 life the extent of wandering is, as a rule, small. Thus, in the extensive 

 marking experiments carried on in the Firth of Forth and St. Andrews 

 Bay by myself, and on the Northumberland coast by Professor Meek, 

 approximately 90 per cent, of those which were recaptured were taken 

 within a few miles of the locality at which they had been liberated, 

 sometimes after an interval of two years or more. Such instances show 

 that the natural range of individuals of certain species may be quite 

 restricted on the whole, and they materially modify the application of the 

 argument drawn from the vastness of the sea. 



With regard to the great fecundity of sea fishes, it is to be observed 

 that some of the arguments used by the opponents of artificial propaga- 

 tion show that the question is not thoroughly understood. Comparison 

 is sometimes made between the number of larval fishes or " fry " turned 

 out from the hatcheries and the number of eggs produced by the female 

 fishes as if the two things were the same. Thus, if 100,000,000 cod 

 larvse are turned into the sea, it is assumed that this result would have 

 been produced if a few score of cod had been left in the sea to 

 propagate naturally, because owing to the f(}cundity of the cod a few 

 scores of females would have spawned that quantity of eggs. By a 

 similar process of reasoning, 100,000,000 larvse of the plaice might be 

 produced by about 330 female plaice (or, taking the males into account, 

 by about double that number) spawning under natural conditions in the 

 sea. Such estimations entirely omit to take into account the measure of 

 protection afforded during the whole of embryonic development and 



* Tioenty-fifth Ann. Rep., Part III., p. 256. 



