Macewicz et al.: Fecundity, egg deposition, and mortality of Loligo opalscens 



313 



females). The maximum number of mature oocytes (246) 

 was never close to the maximum number of ova ( 1726 ) in the 

 oviduct. In addition, spawning females with 900 or more ova 

 in their oviduct had in every case three or more distinctly 

 different stages of postovulatory follicles in their ovaries 

 (Table 2). Thus the oviduct is probably filled by a series of 

 ovulation bouts separated by enough time to produce dis- 

 tinct age classes of degenerating follicles in the ovary. 



Potential fecundity (E P ) 



Potential fecundity (E P ) is the standing stock of oocytes 

 of all stages in the ovary of a mature female just prior 

 to the first ovulation. Finding females at this point in 

 their reproductive cycle was difficult because nearly all 

 specimens had already ovulated. The ovaries of 94% of 

 the 247 mature females, from our research cruises, con- 

 tained postovulatory follicles, indicating that they had 

 recently ovulated and would not be suitable for estimating 

 E P . As can be seen in Figure 7A, spawning females had 

 fewer oocytes in their ovaries than did mature preovula- 

 tory females. The relation between fecundity and squid 

 size is best expressed in terms of dorsal mantle length 

 (L) because L. opalescens lose weight during spawning 

 (Figs. 4, 7C). The data from thirteen mature preovulatory 

 females were used to establish the relationship between 

 potential fecundity and L: 



E P = 85.62L - 6715, [r* = 34.3%] 



where L = dorsal mantle length in mm. 



(14) 



Because the constant was not significant (P=0.146) and 

 the coefficient was (P= 0.036), we forced the regression 

 through zero which resulted in the equation 



E P = 29.8L. 



(15) 



Thus, the average female (129 mm) according to Equation 

 15 had a potential fecundity of 3844 oocytes (SE = 317). 



Clearly it would be preferable if the sample size for the 

 estimate of potential fecundity were larger because thirteen 

 females may not accurately represent theL. opalescens stock. 

 Although the landed catch provides an unlimited supply of 

 specimens, histological detection of postovulatory follicles 

 is not possible because of deterioration of the ovaries. An 

 alternative approach is to use mantle condition of mature 

 females from the catch as a proxy for the preovulatory state. 

 As can be seen in Figure 7C, the mantle condition index (C) 

 of mature females declines as oocyte maturation continues 

 and females deposit eggs. The mature preovulatory females 

 (n=ll, two discs were lost) had a mean C of 0.73 mg/mm 2 

 (SE = 0.02). We believe that the twenty-two mature females 

 from the landed catch with C&0.7 mg/mm 2 had not begun 

 to deposit eggs (Table 3). Because many of them had ovu- 

 lated, we combined our estimates of the standing stock of 

 oocytes (E Y ) with those of ova (E D ) to calculate total fecun- 

 dity (E Y + E D = E YD ), and then regressed total fecundity 

 on length. Although the regression was not significant, the 

 average total fecundity of 3890 oocytes (Table 3) was within 



5% of the potential fecundity of 4083 oocytes computed by 

 substituting the mean length of the twenty-two females 

 (137 mm) in Equation 15. The close agreement between 

 these two values increases our confidence that the potential 

 fecundity equation is accurate despite the low /;. On the 

 other hand, this rough comparison is not a substitute 

 for increasing the sample size of specimens analyzed 

 histologically, because females from the catch may have 

 spawned some of their ova before they were captured. 



Maximum fecundity (E P — E R ) 



Few if any L. opalescens live to realize their full potential 

 fecundity (E P ). The literature on L. opalescens indicates 

 that females that were described as "spawned out," dying, 

 or dead had oocytes in all stages of development except the 

 earliest previtellogenic stage (Knipe and Beeman 1978). 

 In addition, all the spawning females that we collected 

 had some oocytes in their ovaries. Thus, the maximum 

 fecundity that L. opalescens might be expected to realize 

 is the potential fecundity less an estimate of the number 

 of oocytes that might be left in the ovary at death (residual 

 fecundity [E R ]). To estimate residual fecundity we exam- 

 ined the relationship of the standing stock of oocytes in the 

 spawning period with mantle condition index (C), size of 

 the smallest oocyte (D), and dorsal mantle length (L). 



The standing stock of oocytes in ovaries of mature fe- 

 males declines rapidly with decreasing mantle condition, 

 between a C of 0.8 and 0.6 mg/mm 2 , and more gradually 

 over lower mantle conditions (Fig. 7C). A curvilinear rela- 

 tionship also exists between oocyte standing stock and the 

 size of the smallest oocyte (Fig. 7B). Thus the number of 

 past spawnings (decline in oocyte standing stock) appears 

 to be inversely correlated with C and directly correlated 

 with the extent of ovarian maturation as measured by D. 

 To quantify how the standing stock of oocytes changes 

 during the spawning period we fitted a nonlinear model to 

 the fecundity data of 75 mature spawning females (Fig. 7) 

 from our research cruises: 



