ADAMS: LIFE HISTORY PATTERNS IN MARINE FISHES 



selected are likely to be strongly influenced by 

 physical forces in the environment (Pianka 1974). 

 Relationships of this type, e.g., between anchovies 

 and upwelling, should be important considera- 

 tions in management plans for these species. 



Fisheries based on more K selected species will 

 have a high maximum yield per recruit, but there 

 will be fewer fish. Maximum equilibrium yield 

 will occur at later ages of entry into the fishery and 

 at lower levels of fishing mortality. These fisheries 

 would be more susceptible to overfishing and stock 

 depletion. Besides these species' sensitivity to 

 overfishing, more K selected species are much 

 more likely to have sophisticated life history 

 mechanisms (Pianka 1974) which would have to 

 be recognized in a management plan. These 

 mechanisms might include parental care systems 

 such as nesting or live births, mating systems, or 

 territoriality. The more K selected species are 

 much more likely to have strong interspecific rela- 

 tionships, usually competitive ones. The relation- 

 ship between competition and harvesting has been 

 dealt with by Larkin (1963) and Tanner (1975). 

 Additional density independent mortality (fishing 

 mortality) increases the advantage for the popula- 

 tion with a higher population growth rate (i.e., 

 more r selected). Therefore, even low levels of 

 fishing pressure can destabilize a previously sta- 

 ble competitive pair and result in decline of the 

 harvested species. Interestingly, the opposite re- 

 sult is also possible; harvesting pressure can 

 stabilize a previously unstable species pair as 

 Slobodkin ( 1962) found with experimental popula- 

 tions of hydra. 



Fisheries based on more r selected species are 

 likely to be of a boom and bust nature. Although in 

 some years catches in these fisheries will be very 

 large, they will be characterized by erratic produc- 

 tion levels. The most efficient form of harvesting 

 these fisheries will be fleets which are capable of 

 switching between a number of target species rel- 

 atively quickly. 



Fisheries based on more K selected species, in 

 contrast to the boom and bust nature of r selected 

 fisheries, will be characterized by relatively stable 

 population sizes and therefore catch levels. Given 

 some initial measure of year class strength, possi- 

 bly through larval or prerecruitment surveys, the 

 prediction of future catches from that fishery could 

 be made with a fair degree of accuracy. However, 

 once fisheries based on these species become over- 

 fished, it would require a long period for the stock 

 to rebuild to levels which can support economical 



profitable fisheries. An extremely K selected 

 species would only be suitable for trophy fisheries. 



Fisheries based on r and K selected species have 

 been discussed in a comparative sense, but preda- 

 tion (in the case of a fishery , human predation) will 

 also have effects on an individual species. The 

 gene pool of any species is going to contain within 

 it some range of variation of both r and/C selected 

 traits. The effects of increasing fishing mortality, 

 which is assumed to be density independent 

 (Gushing 1975), on life history characteristics has 

 been theoretically analyzed by Roughgarden 

 (1971). The general effect is an increase in selec- 

 tive advantage for the r selected proportions of the 

 gene pool. This would mean an increase in growth 

 rates, reduced age at first maturity, and greater 

 fecundity at age. These trends will be more con- 

 spicuous in species that are relatively more K 

 selected. Species that are more strongly r selected 

 are likely to have less range of variation in this 

 direction. One example of these effects of preda- 

 tion pressure is a comparison of lake trout, Sal- 

 velinus namaycush , populations under heavy pre- 

 dation pressure from the freshwater harbor seal, 

 Phoca uitulina, to populations in nearby lakes 

 without seals (Power and Gregoire 1978). The lake 

 trout populations which were preyed upon by seals 

 had faster growth rates, small maximum body 

 size, reduced maximum age, lower age at sexual 

 maturity, and greater individual fecundity com- 

 pared with populations in lakes without seals. 

 Growth and maturation rates of certain seal 

 species have also increased where populations 

 have been reduced by fisheries (Sergeant 1973). 

 These affects can be attributed to changes in selec- 

 tion pressure resulting from sustained harvesting. 



In summary, r and K selection seems to have 

 been an important evolutionary trend on marine 

 fish populations. The basic hypotheses are con- 

 firmed by the data presented here. The result of 

 patterns in population parameters which arise 

 from r and K selection is that different manage- 

 ment strategies would be appropriate. The value 

 of this approach is likely to be in initial stages of 

 development of a fishery. As a fishery becomes 

 more developed and more specific information be- 

 comes available, a more refined management 

 strategy would become possible. 



ACKNOWLEDGMENTS 



This paper benefited from readings by M. E. 

 Adams, E. O. Garton, E. S. Hobson, W. H. Lenarz, 



