OCEANOGRAPHY AND FISHERIES 309 



require much information from oceanography on the environment of 

 the fish. The first information is that concerning food availabihty; the 

 second is that concerning temperature, sahnity, trace elem.ents and biotic 

 factors which influence the procurement of food it ingests. But the work 

 of fishery biology has been concerned generally with estimates of aver- 

 age growth in populations, and with this as a means of characterizing 

 year-classes and the conditions prevailing from year to year. Recent 

 work has carried the theory further to attempt to use those data on 

 growth as a means of estimating the biomass production of the popula- 

 tion as a whole. Such work will accomplish a practical effectiveness, 

 however, only after the underlying physiology of nutrition and growth 

 have been studied further, and this will mean, as in the study of nutri- 

 tion and growth of domestic animals, that there must be controlled ex- 

 periments in which both food supply and environmental factors are at 

 least precisely measured if not actually controlled. 



In this field of enquiry, taking it to be the responsibility of fishery 

 biology to measure the growth of the population, the contribution of 

 oceanography is two fold: initially, in aiding the description and analysis 

 of these systems; subsequently, in providing data for a prediction sys- 

 tem. In the initial phase the contribution is of data on all factors which 

 might directly or indirectly affect the nutrition and growth of the fish. 

 In the prediction phase, the data would concern certain critical factors. 



Reproduction:— Although, in the fishing theory equation this term 

 refers essentially to recruitment into fishable stocks, the fishery biologist 

 has some concern with the whole range of phenomena which lead to 

 the reproductive act and those which lead from that act to recruitment. 

 That is to say, there is a concern with sex ratios and fecundity, with 

 length and age at first maturity, and (within each season) of the 

 maturation of the gonads, v/ith the spawning act itself (including fer- 

 tilization), with embryonic development and hatching, with larval and 

 post-larval development, and with growth and survival through these 

 and the young-fish stages. Some workers consider that the only practi- 

 cable approach to the problem of replenishment of the stock is by way 

 of measurement of recruitment as it is taking place, or of the potential 

 recruits shortly before they enter the fishery. Other workers contend 

 that it is possible to enter more deeply into the system and to attempt 

 some measurement of the series which connects spawners with recruits. 

 Among these latter there are some who believe that, although in gen- 

 eral the number of eggs produced at each spawning is always far in 

 excess, in numbers, of the number of individuals which survive to be 

 recruits to the fishery, so that little connection can be found between 

 the number of eggs spawned and the subsequent recruitment, the brood 



