Equilibrium yield (EY) : 



the yield in weight taken from a fish stock 

 when it is in equilibrium with fishing of a 

 given intensity, and (apart from effects of 

 environmental variation) its biomass is not 

 changing from one year to the next. (Ricker, 

 1975, p. 3) 



the annual or seas.onal harvest which allows 

 the stock to be maintained at approximately 

 the same level of abundance (apart from the 

 effects of environmental variation) in 

 succeeding seasons or years . (North Pacific 

 Council, 1978 DEIS/FMP Groundfish Fishery in 

 the Bering Sea/Aleutian Island Area, p, 5) 



Maximum net productivity (MNP) : 



the greatest net annual increment in population 

 numbers or biomass resulting from additions 

 to the population due to reproduction and/or 

 growth less losses due to natural mortality. 

 (NMFS operational definition, 50 CFR 216.3) 



Maximum sustainable yield (MSY) : 



the largest average catch or yield that can 

 continuously be taken from a stock under 

 existing environmental conditions. (Ricker, 

 1975, p. 4) 



the greatest harvest that can be taken from a 

 self-regenerating stock of animals year after 

 year while still maintaining a constant 

 average size of the stock. (Holt and Talbot, 

 1978, p. 22) 



Natural mortality: 



deaths from all causes except man's fishing, 

 including predation, senility, epidemics, - 

 pollution, etc. (Ricker, 1975, p. 5) 



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