THE APPLICATION OF COMPARATIVE POPULATION 

 STUDIES TO FISHERIES BIOLOGY — AN EXPLORATION 



S. J. Holt 



Fisheries Division, F.A.O., Rome 



INTRODUCTION 



As nations have intensified their fishing activities during the past few decades, 

 so the attention of marine biologists concerned with the improvement of 

 fisheries has become focused on the need to predict catches and particularly 

 the effects on catches of changes in the fishing activity, with a view to 

 proposing steps — which may include legislation — to ensure that increasing 

 input will continue to give sufficiently increasing returns. Thus, while many 

 biologists continue studies intended to result in higher efficiency of fishing 

 operations — for example observing the behaviour of fish in relation to 

 natural environmental factors and to fishing gear — others have considered 

 the relations between catches, population sizes and fishing activities. In doing 

 this they have pursued three lines of investigation. In the first line the 

 dynamics of entire eco-systems are considered, with particular reference to 

 the flow of energy and materials from one trophic level to another, so that 

 the yield of animals and plants directly useful to man is seen as a function of 

 the quahty, quantity and disposition of inorganic materials and of incident 

 energy. If the dynamic relations between the significant elements of a par- 

 ticular eco-system are understood and their rates of action measured, it may 

 theoretically be possible to predict at least the order of magnitude of actual 

 and potential yields to be obtained by certain types and patterns of fishing 

 operations, the changes in these yields which might be expected to result 

 from certain kinds of intervention in the system, as by transplantations, 

 artificial mixing or fertihzation, and so on. Studies of this kind are extremely 

 complex and their results cannot yet be regarded as having practical appUca- 

 tion, at least in sea fisheries. 



In the second line of investigation the population growth pattern of a fish 

 stock or of a group of stocks is considered, growth increment, and hence 

 capacity to yield, being regarded primarily as a function of the size (in 

 numbers or weight) of the stock. It has been assumed that population growth 



5 



