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Fishery Bulletin 1 10(4) 
B 
Age 
Fishing mortality rate 
Figure 2 
(A) Reproductive value incorporating survival, maturity, batch fecun- 
dity, and 4 qualitative patterns of annual number of batches. Results 
are based upon these qualitative patterns are shown in relation to 
the value at age 1, computed as a function of age under natural 
mortality only. (B) Age of maximum reproductive value as a function 
of fishing-induced mortality rate. In both panels, annual number of 
batches spawned (shown in Fig. 1A) per mature female are constant 
(i = l, solid line), increasing (i = 2, dotted line), decreasing (f = 3, dash- 
dot line), and dome-shaped (i = 4, dashed line). 
Measures of mean spawning frequency and duration 
are commonly applied to derive estimates of spawning 
stock biomass through the daily egg production method 
(DEPM) in species with indeterminate fecundity (Stra- 
toudakis et ah, 2006). Although this method is difficult 
to apply with precision, the DEPM has been used most 
often in assessments of short-lived clupeoid species for 
which direct methods of estimating spawning biomass 
are preferred (Stratoudakis et al., 2006). Because this 
approach is not explicitly dependent on age structure, 
the implications of size and age variation should be 
minimal. However, Priede and Watson (1993) provide 
an example of the difficulties in applying the DEPM to 
a longer-lived species, including the case when older At- 
lantic mackerel ( Scomber scombrus ) begin spawning ear- 
lier than younger mature females. The knowledge that 
older adults may spawn earlier, over a longer season, 
or more often to produce more batches may help guide 
sampling designs. Sampling of adults should be repre- 
sentative of a population or enough information on stock 
structure should be gathered to properly weight the 
adult data used for DEPM (Stratoudakis et ah, 2006). 
In contrast to application of egg production methods 
to short-lived species, our results may be most informa- 
tive for estimates of reproductive potential used in age- 
structured assessments of relatively long-lived species 
