"adequate levels," or of OSP for mammals as defined conceptual- 

 ly in the MMPA, would be a very difficult task. However, the 

 question of OSP levels should have been raised, even if con- 

 sidered not answerable at present. 



The dependence of predators on anchovies was discussed 

 in the plan, but not the existence of potential impact on al- 

 ternative prey. Anchovies have been estimated to make up 45% 

 of the average biomass and 507 o of the production of small 

 schooling fish (Green, 1978). The plan concluded that benefit 

 to the nation does exist when fish are left in the water 

 because they support commercially and recreationally valuable 

 fish and squid as well as "non-valued birds and mammals." OY 

 levels as formulated, considerably less than MSY , would contrib- 

 ute to leaving fish in the water and maintaining predator 

 stocks . 



The question of whether predator populations would be sup- 

 ported sufficiently was not addressed in detail in the plan. 

 The analysis of predator needs and interactions in the plan was 

 confined to the observation that during 1951-1961 when spawning 

 biomass was below 2 million tons (as opposed to the present 

 3 to 4 million tons), predators did not appear to decline. How- 

 ever, no information on marine mammal populations is available 

 to support or refute that assumption. The plan concluded that 

 long term average anchovy biomass in excess of 2 million tons 

 should not have a severe adverse effect on predators. Under 

 the OY formula, spawning biomass was anticipated to average 2.5 

 million tons. It was expected to fluctuate around this average 

 and to fall below 1 million tons for one year in five. 



The relationship of natural populations of predators to 

 fluctuations in their prey is a complex one and not well worked 

 out theoretically at the present state of the art of ecology. 

 Populations of long lived predators such as mammals may not 

 respond quickly to changes in prey abundance. The crucial 

 parameter of survival of young to sexual maturity may respond 

 over one to several years to such changes in abundance. How- 

 ever, because of the late age of sexual maturity, it would take 

 a longer time for the impact of several years of low juvenile 

 survival to become apparent in the overall population size 

 (Green, 1977). The question of time lags in predator prey 

 relationships is a classic one, and merits more consideration 

 in multi-species fishery management (May, e_t al_. , 1979). For 

 some predators, reproductive success may respond to a threshold 

 value of prey availability, such as a minimum required prey 

 density, so that the relationship of predator abundance to prey 

 abundance is not simple. Even though relationships are not 



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