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



317 



0.2 



0.4 0.6 OS 



Mantle condition index (mg/mm 2 ) 



1.0 



Figure 9 



Standing stock of oocytes and ova as a function of mantle condition 

 index for 60 mature females taken in the fishery (triangles) and 87 

 mature females taken in research surveys (circles I. The line (not 

 drawn to the data points plotted) represents a possible relation if 

 losses in body weight were equivalent to the weight of the spawn 

 released, computed for an average female (130 mm) where the 

 starting point is her potential fecundity of 3874 oocytes and ends 

 with eggs and a mantle condition index of 0.281 mg/mm 2 . 



possible, but it seems unlikely for the nearly exhausted 

 L. opalescens that are near the end of their life. 



Longevity and egg deposition rates 



Inferences regarding the longevity of adult spawning L. 

 opalescens are the best proxy we have for the mortality 

 rates of spawning adults. Previous observers (McGowen, 

 1954; Fields, 1965) suggested that females deposited all 

 their eggs in one night and death soon followed. On the 

 other hand, it is unreasonable to expect that a reduction 

 of 609 in body weight and the maturation and deposition 

 of up to 78% of the potential fecundity could take place 

 in 24 hours. Our data on fecundity and mantle condition 

 show an initial rapid decline in the number of oocytes 

 followed by a more gradual decline (Fig. 7C), indicating 

 an initial period of intense egg laying may be followed 

 by a longer one where fewer eggs are deposited. It is also 

 important to recognize that ovaries of spawning animals 

 contain a wide range of oocyte sizes (Fig. 6), includ- 

 ing many small unyolked oocytes (0.3-1 mm) that may 

 mature and be deposited during the spawning period. 

 It is unlikely that all these processes (body resorption, 

 dynamic changes in rates of egg deposition, and matura- 

 tion of small unyolked oocytes) could occur in one 24- 

 hour period. Spawning periods longer than two weeks 

 also seem unlikely because mature L. opalescens females 

 may require extensive feeding periods and prolonged ab- 

 sences from the spawning grounds; these behaviors are 

 inconsistent with our energetic analysis in the preceding 

 section. Our analysis indicated that the observed reduc- 

 tion in eggs can be fairly well explained by the observed 

 reduction in squid dry weight. 



Egg deposition rates provide another way to infer the 

 longevity of spawning squid. The best evidence for the 

 rate of egg deposition is provided by females judged, on the 

 basis of their high mantle condition ( C^O.700 mg/mm 2 ), to 

 be new recruits to the spawning grounds. Considering only 

 those new recruits that have ovulated (postovulatory fol- 

 licles present or ova in the oviduct ), the difference between 

 their average oocyte standing stock (£ y =2571) and their 

 average potential fecundity (£ P =4020) was equivalent to 

 a reduction of 1449 oocytes or 36% of their potential fecun- 

 dity (Table 5). If the difference is spawned in 24 hours or 

 less, then 36% can be considered as an average for the first 

 day of egg deposition. Instead of using the reduction of oo- 

 cyte standing stock, one could consider the standing stock 

 of ova (E D ) to be equivalent to the first day ( 24-hour period ) 

 of spawning in these new recruits. Their average E D was 

 1073 or 27% of their potential fecundity. Thus depending 

 on the criteria, the first day of spawning might be 27% to 

 36% of the potential fecundity. We prefer 36% because it is 

 unaffected by any losses due to egg deposition. 



The standing stock of ova (E D ) of spawning females 

 with lower mantle condition (C<0.7 mg/mm 2 ) averaged 

 9% of their potential fecundity. If the average E D from 

 these females is a crude measure of daily egg deposition 

 rates after the first day, then we calculate it would take 

 seven additional days [U00%-36%)/9%] to use up the 

 remaining potential fecundity or a total spawning period 

 of eight days. Eight days is an extreme value because 

 an adult L. opalescens has never been taken with zero 

 oocytes. The minimum residual fecundity was 22% of the 

 potential which is roughly equivalent to about two days 

 of egg deposition. Thus, six days may be a better guess 

 of the maximum longevity of spawning L. opalescens. 



