LO: EGG PRODUCTION OF NORTHERN ANCHOVY 



CalVET net, and the larval data were collected 

 with both bongo oblique tows and the CalVET 

 nets. The egg and larval catches by age group were 

 standardized, that is, corrected for possible biases 

 caused by extrusion through the mesh, day-night 

 difference in avoiding the net, variation in the 

 amount of water filtered, and the variation of 

 larval growth rates which is both temperature and 

 food dependent (Methot 1981; Lo 1983). The stan- 

 dardized daily egg and larval production esti- 

 mates per 0.05 m^ sea surface area in CalCOFI 

 regions 4, 7, 8, and 11 for January-April 1979-81 

 are given (Table 1, Fig. 3). 



The IMR for the egg stage was believed to be 

 constant, zi(t) = a, (Stauffer and Picquelle foot- 

 note 6), whereas the IMR for larval stage was 

 found to be age dependent Z2it) = pit (a Pareto 

 hazard function, Johnson and Kotz 1970). I first 

 calculated sample IMR z{ti ) = iPn-i - Pt, )l{ti - 

 ti-i)IPti which is an approximation of dS{t)ldtl 

 Sit) at various ^ for < ^ < 20 d using 1980 

 standardized egg and larval data listed in Table 1. 

 The 1980 egg and larval production and age data 

 were further combined so that 2 (^) > for all t. 

 The relationship between zit) and t determined 

 the function form of 2(0 (Table 2). The zitYs were 



19791 



T9801 



^ 12.0 



H 90 h 

 O 



Q 6.0 |- 



O 



CC 



^ 3.0 h 



< 



c 

 o 



u 



3 

 ■D 



O 



w 



Q. 

 >• 



"(5 



"O 



0.0 



^ 



12.0 

 9.0 

 6.0 

 3.0 



Q I Q Q— I 0.0 



J] 



19811 



o , o 



12.0 

 9.0 

 6.0 



3.0 



g IQ Q I 0.0 



DD 



. ° °.° ° 



3.0 

 2.0 

 1.0 

 0.0 

 -1.0 



0.0 5.0 10.0 15.0 20.0 0.0 5.0 10.0 15.0 20.0 0.0 5.0 10.0 15.0 20.0 



AGE (in days) AGE (in days) AGE (in days) 



■J 



- a 



£ -2.0 



3.0 

 2.0 

 1.0 

 0.0 h 

 -1.0 



a 



-2.0 



3.0 

 2.0 

 1.0 

 0.0 

 -1.0 

 ' o ' -2.0 



■o 



o o 



0.0 5.0 10.0 15.0 20.0 0.0 5.0 10.0 15.0 20.0 0.0 5.0 10.0 15.0 20.0 



3.0 

 2.0 

 1.0 

 0.0 

 -1.0 I- 



J -2.0 

 -2.0 -1.0 0.0 1.0 2.0 3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 



In (age) In (age) In (age) 



Figure 3. — Daily egg and larval production of northern anchovy per 0.05 m* (Pt) by age in days (t) and their log transformations 

 (ln(Pt ) ), 1979-81. A linear relationship between ln(Pt ) and t indicates a constant instantaneous mortality rate (IMR) and a curvilinear 

 relationship between ln(Pt ) and t indicates an age dependent IMR. Squares are egg data and open circles are larval data. 



143 



