APPENDIX 4 

 SCIENTIFIC PRINCIPLES AND TERMS 



population size is below the level ot maximum net 

 production. This is often referred to as their opti- 

 mum sustainable population (OSP) level. 



The Marine Mammal Protection Act (MMPA) 

 defines OSP to mean "with respect to any popu- 

 lation stock, the number ot animals which will 

 result in the maximum productivity of the popu- 

 lation or the species, keeping in mind the carry- 

 ing capacity of the habitat and the health of the 

 ecosystem of which they form a constituent ele- 

 ment." For operational purposes, NMFS and the 

 U.S. Fish and Wildlife Service (USFWS) have in- 

 terpreted this definition to mean "a population 

 size falling within a range from the population level 

 of a given species or stock which is the largest sup- 

 portable within the ecosystem to the population 

 le\el that results in maximum net productivity 

 (MNP)." Maximum net productivity is defined as 

 "the greatest net annual increment in population 

 numbers or biomass resulting from additions to 

 the population due to reproduction or growth less 



loses due to natural mortality." 



Potential biological removal (PBR) is the maxi- 

 mum number of animals, not including natural 

 mortalities, that may be removed from a stock 

 while allowing that stock to reach or stay at its 

 optimum sustainable population level (50-100% 

 of its carrying capacity. N^.^ is a conservative esti- 

 mate of abundance used to estimate PBR and pro- 

 vides reasonable assurance that the stock size is 

 equal to or greater than the estimate. 



Protected species of marine mammals and sea 

 turtles may also be classified as threatened or en- 

 dangered under the Endangered Species Act. A 

 species is considered threatened if it is likely to 

 become an endangered species in the foreseeable 

 future throughout a significant portion of its range. 

 A species is considered endangered if it is in dan- 

 ger of extinction throughout a significant portion 

 of its range. In addition to some marine mam- 

 mals and all sea turtles, several Pacific Coast salmon 

 stocks are now listed as threatened or endangered. 



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