■90 SECTIONAL ADDRESSES. 



for its nutrition and which we call plant. In this case the plants 

 are spores of algae, diatoms, etc., and their abundance as food again 

 depends on the amount of the light of the sun — the ultimate source, 

 it might seem, of all hfe. 



A method of ascertaining the age of fishes was sought purely to 

 correlate age with growth in comparison with the growth of air-living 

 vertebrates. This method was found in the rings of growth in the 

 scales, and now the ascertaining of age-groups in herring shoals enables 

 the Norwegian fishermen to know with certainty what possibilities and 

 probabilities are before them in the forthcoming season. From the 

 work on the blending together of Atlantic with Baltic and North Sea 

 water off the Baltic Bight and of the subsequent movements of this 

 Bank water, as it is termed, into the Swedish fiords can be understood, 

 year by year, the Swedish herring fishery. It is interesting that these 

 fisheries have been further correlated with cycles of sun spots, and 

 also with longer cycles of lunar changes. 



The mass of seemingly unproductive scientific inquiries undertaken 

 by the United States Bureau of Fisheries, thirty to fifty years ago, 

 was fhe forerunner of their immense fish-hatching operations, whereby 

 billions of fish eggs are sti-ipped year by year and tha fresh waters 

 of that country made into an important source for the supply of food. 

 The study of the growth stages of lobsters and crabs has resulted in 

 sane regulations to protect the egg-carrying females, and in some 

 keeping up of the supply in spite of the enormously increased demand. 

 Lastly, the study of free-swimming larval stages in mollusca, stimu- 

 lated immensely by their similarity to larval stages in worms and 

 starfishes, has given rise to the establishment of a successful pearl- 

 shell farm at Dongouab, in the Eed Sea, and of numerous fresh-water 

 mussel fisheries in the southern rivers of the United States, to supply 

 small shirt buttons. 



Fishery investigation was not originally directed to a more ambitious 

 end than giving a reasonable answer to a question of the wisdom or 

 unwisdom of compulsorily restricting commercial fishing, but it was 

 soon found that this answer could not be obtained without the aid 

 of pure zoology. The spread of trawling- — and particularly the intro- 

 duction of steam trawling during the last century — gave rise to grave 

 fears that the stock of fish in home waters might be very seriously 

 depleted by the use of new methods. We first required to know the 

 life histories of the various trawled fish, and Sars and others told 

 us that the eggs of the vast majority of the European marine food 

 species v\>ere pelagic ; in other words, that they floated, and thus could 

 not be destroyed, as had been alleged. Trawl fishing might have to 

 be regulated all the same, for there might be an insufficient number 

 of parents to keep up the stock. It was clearly necessary to know 

 the habits, movements, and distribution of the fishes, for all were 

 not, throughout their life, or at all seasons, found on the grounds it 

 was practicable to fish. A North Sea plaice of 12 in. in length, a 

 quits moderate size, is usually five years old. The fact that of the 

 female plaice captured in the White Sea, a virgin ground, the vast 

 majority are mature, while less than half the plaice put upon our 



