The spawning habits of the tunas are generally as outlined 

 aboveo The life of the immature fish is almost completely unknown, 

 but when they have attained a certain size they f c rm large schools 

 and begin to migrateo The tuna fisheries are based on the utiliza- 

 tion of this habito 



Considering the whole extent of the seas in which they are 

 distributed^ the population per unit of area is no doubt small in 

 comparison with that of other fishery resources, but the population 

 within the scope of schools that are formed is by no means small. 

 The reason for the markedly unstable character of the tuna fisheries 

 in comparison with the coastal and bottom fisheries is not that the 

 absolute quantity of the resource is inferior to that of the 

 demersal fishes o The problem is that the organization and form of 

 the schools and the factors controlling their migration^, congrega- 

 tion, and dispersal are extremely difficult of investigation^ and 

 consequently our knowledge concerning them is extraordinarily pooro 



A look at present conditions in the tuna fisheries reveals 

 that the mox^ progressive among the operators engaged in these 

 fisheries are gradually coming to raise their voices more and more 

 in demands for scientific backingo But at present the only applica- 

 tion of scientific methods is merely the measuring of surface water 

 temperatures in order to locate fishing grounds, and not one step 

 has been taken in advance of a condition where operations are still 

 based on the experience and judgment of the fishermano 



bo The problem of fishing gear 



The structure of longlines is not standardized, but has 

 changed from period to period and varies according to the species 

 fished for. There are also local peculiarities, constructions 

 which are thought to be best suited to conditions in various sea 

 areaso ^furthermore, within the same region individuals construct 

 their lines differently, each fisherman using the type of gear 

 which he thinks most suitable on the basis of his personal experience 

 and studyo 



The factors which should determine the structure of the lines 



ares 



io Catch efficiency 



iio Simplicity and ease of operation 



iiio Strength 



ivo Expense of construction 



It is not thought that factors iii and iv offer any great difficul- 

 ties, but i and ii, particularly i, involve some rather important 

 problemso 



78 



