258 R. J. H. BEVERTON 



that it has been shown to exhibit changes in response to environmental 

 conditions which would seem to have an adaptive value (NikoFskii, 1950), 

 unless there is also a fairly clear relation between egg-production and number 

 of surviving progeny, and this has seldom been established in fish. The 

 various phases of the life-history of a fish species constitute virtually 

 independent systems. The interactions within a population of larval fish, for 

 example, and between that population and its environment, both physical 

 and biotic, are entirely different from those of the adult fish; and it is 

 evidently possible, as in plaice, for the density of the adult phase to be little 

 influenced by environmental restraints and yet for the population as a whole 

 to be kept closely in check by compensatory processes confmed to an earlier 

 stage of the life-history. Quantitative studies on the adult phase of exploited 

 fish populations have advanced a good deal in recent years, due partly to the 

 ease with which age can be determined in many species and to the wealth of 

 information which can be obtained directly or indirectly from commercial 

 catches and fishing activity. Perhaps as much or more is known about their 

 dynamics as about those of any other group of natural populations; yet it 

 seems that a real insight into the long-term dynamics offish populations can 

 come only from a better understanding of events during the earlier stages of 

 the life-history in relation to the environment. 



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