SMITH ET AL.: MORTALITY RATES OF SARDINE AND ANCHOVY EGGS OFF PERU 



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7 4° 



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Figure 1. — Coastline of Peru and egg survey stations and statistical regions. 

 Egg sampling stations are 3 miles apart in the cross-shelf plane. Regions for 

 statistical summaries are coded. The first digit of each number refers to the 

 north "1", central "2", or south "3" sectors of the coast. The second number 

 refers to the inshore "1", offshore "2", or seaward "3" regions of each sector. 

 In text, codes referred to as IMARll, IMAR12, etc. to distinguish the codes 

 from numbers. Original station positions and equations for plotting are in 

 Smith et. al. (1983). 



Anchovy and sardine eggs were grouped in 12 h 

 intervals. Newly spawned eggs collected during 

 the spawning interval and older eggs collected 

 during hatching were eliminated from the calcu- 

 lations. The remaining egg counts were re- 

 gressed on age to fit a mortality function of the 

 egg data. The daily egg production was then 

 estimated by zero intercept of the exponential 

 mortality function. The following exponential 

 model can be fit to the egg data by the nonlinear, 

 least squares regi'ession (Stauffer and Picquelle 

 1980^): 



Po = P, e-'* 



where P^ = daily egg production; 



P,= number of eggs of age t, sampled 

 during the time interval i,, f,+i; 

 t- time elapsed between spawning 



and the /th time interval; and, 

 Z= instantaneous daily rate of egg 

 mortality. 



The Pq is the intercept of the exponential curve. 

 The model assumes that all eggs are spawned 

 and fertilized at an instant, that the eggs have a 

 constant rate of mortality, and that the sampling 

 was representative and includes all areas where 

 eggs may be found. 



'Stauffer, G. D., and S. J. Picquelle. 1980. Estimates of 

 the 1980 spawning biomass of the central subpopulation of 

 northern anchovv. U.S. Dep. Commer., NOAA, NMFS 

 SWFC Adm. Rep. LJ-80-09, 41 p. 



RESULTS 



Peruvian anchovy and Pacific sardine co-occur 

 along the north and central coast of Peru 



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