LIFE HISTORY PATTERNS IN MARINE FISHES AND 

 THEIR CONSEQUENCES FOR FISHERIES MANAGEMENT 



Peter B. Adams* 



ABSTRACT 



Natural selection operates at the life history level to maximize the number of surviving offspring. Life 

 history characteristics will vary in consistent patterns to meet this constraint. When theoretical 

 patterns in life histories were investigated in terms of r and K selection and compared with actual 

 trends in life history characteristics of fishes, the agreement between observed and predicted trends 

 was significant. The effects of harvesting on stocks with these life history trends were investigated 

 and it was found that K selected type species would be highly sensitive to overfishing and, once 

 depleted, recovery would require a long time. 



The ecological and genetic properties of a species 

 are intimately linked. The morphological and re- 

 productive characteristics, population sizes, and 

 genetic frequencies of species are adjusted to their 

 environments by natural selection. Species in- 

 habiting different environments show different 

 patterns of life history characteristics. The rela- 

 tionship among habitat, ecological strategies, and 

 population parameters has been termed r and K 

 selection (Mac Arthur and Wilson 1967) and/or op- 

 timal life histories ( Gadgil and Bossert 1970). This 

 body of theory is based on the assumption that 

 natural selection operates on these characteristics 

 in order to maximize the number of surviving 

 offspring produced. Under an environmental re- 

 gime with a large component of unpredictable, 

 nonselective, mortality an organism will allocate 

 a larger portion of its resources to reproductive 

 activities (an r strategist). Conversely the optimal 

 allocation of resources for a population subjected 

 to a high proportion of predictable, selective mor- 

 tality will be toward increasing individual fitness, 

 frequently through competitive ability (a K 

 strategist). With the number and variability of 

 factors operating on any particular species, no 

 species is going to be an r or X strategist in an 

 absolute sense. A species will only occupy a rela- 

 tive position on the r and K continuum. 



In fisheries biology, the value of comparative 

 studies of life history parameters has long been 

 recognized (Holt 1962; Beverton 1963; Gushing 

 1971; Alverson and Carney 1975). These life his- 



' Southwest Fisheries Center Tiburon Laboratory, National 

 Marine Fisheries Service, NOAA, Tiburon, CA 94920. 



tory parameters should vary in a consistent pat- 

 tern which can be predicted from the theory of r 

 and K selection. In this paper, these predictions 

 are tested with life history parameters from major 

 groups of marine fishes. The theory has implica- 

 tions for management, particularly when fisheries 

 are in the initial stages of development. 



THEORY OF r AND K SELECTION 



The theory of r andX selection is based on two 

 assumptions about the allocation of a population's 

 resources between competitive and reproductive 

 functions (Pianka 1974; Gadgil and Bossert 1970; 

 Schaffer and Gadgil 1975). The first is that there is 

 a positive relationship between the amount of re- 

 sources spent on an offspring and the fitness of 

 that offspring. The second assumption is that any 

 species only has a fixed amount of resources avail- 

 able. This results in an inverse relationship be- 

 tween the number of offspring produced and their 

 average fitness. The criterion for success in 

 natural selection is the number of surviving 

 offspring that a parent produces (Crow and 

 Kimura 1970). Therefore, the best reproductive 

 strategy is a compromise between two conflictmg 

 demands: production of the largest possible total 

 number of offspring {r selection), and production of 

 offspring with the highest possible fitness ^ selec- 

 tion). The particular point of compromise for any 

 species will be a function of the selection factors 

 operating on that species and would be that 

 species' position on the r and K continuum. 



The second part of the theory concerns the rela- 

 tionship between these life history strategies and 



1^ 



Manuscript accepted September 1979. 

 FISHERY BULLETIN; VOL. 78, NO. 1. 1980. 



