CalCOFI Reports, Vol. 27, 1986 - California Cooperative Oceanic ...

BINDMAN: 1985 NORTHERN ANCHOVY SPAWNING BIOMASSCalCOFI Rep., Vol. XXVII, 1986500 r400L$ 300w3[ 200100025 cOVARY-FREE WEIGHT (9)sired mi was 25 females. The variance equation (7) wasmodified because of the extra source of variation fromthe fecundity/ovary-free weight regression (Draperand Smith 1966):var(r) = C (mj/fi)2[(Fj-F)2/(n-l) + S1,'/85i + (w;*-ivh*)2var(b)]/n (10)where sh2 = 3,748,191 is the variance about the re-- gression,W,* = average ovary-free weight for the ith- traw 1,wh* = 15.43 g, average ovary-free weight ofthe 85 hydrated females used in the regression,vir (b) = 2,453, variance of the slope of the regression,andn = 63, the number of positive trawls.The average batch fecundity and its variance appear inTable 2.OVARY-FREE WEIGHT (g) (Regression)Figure 8. Frequency distributions of ovary-free weight for the entire survey(top) and for the females with hydrated ovaries used to estimate the batchfecundityiovary-free weight regression.Spawning FractionThe spawning fraction is the proportion of maturefemales that spawned on the night prior to capture(day-1 spawners). The spawning fraction, S, and itsvariance were estimated using equations 6 and 7 whereyi = Si was the spawning fraction found from the ithtrawl. The desired mj-the sample size pertrawl- was 25. Strong evidence indicates that femalesspawning on the night of capture (day-0 spawners) areoversampled by the trawl (Picquelle and Hewitt 1983).To account for this, I adjusted mi by assuming thatthere was an equal incidence of day-0 and day-I30 spawning fish and hence substituting the day- 1spawners for the day-0 spawners. The frequency distri-25bution of the spawning fraction appears in Figure 9.The estimate of S and its variance are found in Table 2.20> Female Fraction0zThe female fraction of the population by weight isWa 15the parameter R. Equations 6 and 7 were used where yjs a= Ri, the total weight of females in a subsample of ap-U.proximately 50 fish divided by the total fish weight.10For each trawl, average weights of male (n = 5) and female(n = 25) fish were measured, and the weights of5hydrated females were adjusted using the regressiongiven in equation 8. These average weights were usedto estimate the total female weight and the total fish0o 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 weight. The frequency distribution of R is givenPROPORTION OF DAY-1 SPAWNERSin Figure 10; the estimate and variance are shown inFigure 9. Frequency distribution of spawning fraction.Table 2.21