Lo et al. Biomass and reproductive status of Sardmops sagax off the Pacific coast. 
181 
Table 2 
Gross anatomical classification of female and male Pacific sardine ( Sardinops sagax) gonads. 
Gonad code 
Female: Ovary description 
1 
Clearly immature : Oocytes are not visible. Ovary is very small, translucent or clear, and thin, but with 
rounded edges (torpedo shaped). 
2 
Intermediate'. Individual oocytes are not visible to the unaided eye (no visible yolk or hydrate oocytes in 
the ovaries), but ovary is not clearly immature. Includes possible maturing and regressed ovaries. 
3 
Active : Yolked oocytes in ovaries visible to the unaided eye in any size or amount, including the smaller 
opaque oocytes (around 0.4-0. 5 mm) to the large yellowish oocytes (about 0.6-0. 8mm). 
4 
Hydrated : Hydrated oocytes are present, yolked oocytes may also be seen. Hydrated oocytes (large and 
transparent), from few to many, or even if loose or “oozing” or “running” from ovary, qualify for this 
class 
Male: 
Testis description 
1 
Clearly immature'. Testis is very small, knife shaped, translucent or clear, and thin with a flat ventral 
edge. 
2 
Intermediate'. No milt is evident and testis is not clearly immature (includes maturing or regressed 
testes). 
3 
Active: Milt is present either oozing from the gonopore, in the duct, or in the testis (observed when the 
testis was cut). 
the threshold was one egg/min. We obtained the SST 
for CUFES samples with >0.5 eggs/min as a proxy for 
the oceanographic conditions. No biological variables 
such as zooplankton volume (Lynn, 2003) were collected 
during these surveys. 
Daily egg production 
The daily egg production (P 0 ) is defined as the newly 
spawned eggs produced per 0.05 m 2 per day, where 0.05 
m 2 was the surface area covered by the CalVET net tow 
The daily rate of egg production and the daily specific 
fecundity rate from adult parameters (Lasker, 1985) 
are needed to compute spawning biomass. In California 
waters, sardine egg data from CalVET tows and yolksac 
larval data from both CalVET tows and bongo nets, and 
sardine ages were used to model the embryonic mortal- 
ity curve, a negative exponential curve (Lo et al., 1996, 
2005): 
P l = P 0 e^ zt \ (3) 
where P t = the daily production rate at age t (days); 
2 = the daily instantaneous embryonic mortality 
rate; and 
P 0 = the intercept, is the daily egg production at 
age zero. 
Because few eggs were caught during CalVET net tows 
in July surveys and no eggs were caught in March 
surveys (Fig. 2-5, Table 3), no attempt was made to 
estimate egg production for the March surveys. For July 
surveys, it was impossible to model the egg mortality 
curve because the mortality curve requires sufficient 
data on egg abundance for each egg stage and age. 
Instead, we used an alternative algorithm to estimate 
P 0 , an integral method (P 0 1) based on the standing stock 
of eggs from CalVET tows. 
The estimate of P 0 (P 0 7 ) was based on the relation- 
ship between the mean catch of eggs from CalVET 
tows (Y) and egg production (P 0 ) through the inte- 
gral of P t over the period from spawning to hatching 
(t h ). The mean catch of eggs from CalVET tows was 
a weighted average with the area in each stratum as 
weight. This method requires prior knowledge of the 
egg mortality rate and the temperature-dependent 
hatching time: 
*h th 
Y=^P t dt = ^ P 0 e~ zt dt. (4) 
o o 
Integrating the above equation yields the estimate of 
P 0 as a function of the mean egg density, Y, incubation 
time, t h , and the daily instantaneous mortality rate, 2 : 
with variance calculated by using the delta method: 
<3Pa J 9 d Pv 1 9 
var( P 0 7 ) = ( J r var( 2 ) + ( - )" var( Y), 
az oY 
Y[1 - exp(- 2 ^ )(1 + zt h )] 2 , , 
= ( - 0 ) var( 2 ) 
[1-exp {-zt h )Y 
+( ) 2 var(Y). 
1 - exp( -zt h ) 
