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



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Figure 1 



Collection locations for female Loligo opalescens during two joint research cruises during 

 1998 by California Department of Fish & Game (CDF&G) and National Marine Fisheries 

 Service (NMFS) and for three immature females (triangles) collected during February 

 2000 (CDF&G). 



to monitor the fecundity of the catch that avoids the costly 

 process of counting all oocytes and ova. 



In this study we consider four aspects of the fecundity 

 of L. opalescens: potential fecundity, minimum residual 

 fecundity, maximum fecundity, and the fecundity depos- 

 ited by the average female in the population. Potential 

 fecundity, or potential lifetime fecundity, is the standing 

 stock of all oocytes in the ovary just before the onset of the 

 first ovulation. Because L. opalescens are semelparous, the 

 standing stock of all oocytes in the ovary just before first 

 ovulation equals their potential lifetime fecundity. Clearly, 

 once ovulation and spawning (deposition of ova in egg cap- 

 sules on the sea floor) begin, the standing stock of oocytes 

 can no longer be considered a measure of the potential 

 fecundity of the female. Minimum residual fecundity is 

 the minimum number of oocytes that might be expected 

 to remain in the ovary at death. Because ovaries of dying 

 L. opalescens contain oocytes (Knipe and Beeman, 1978), 

 only a portion of the potential fecundity will be spawned 

 in their lifetime. We use ancillary information on L. opal- 

 escens (an index of mantle condition and extent of ovarian 

 development) to project what the minimum residual may 

 be. Maximum fecundity (potential fecundity less the mini- 

 mum residual fecundity) is the maximum number of eggs 

 a female might be expected to deposit in a lifetime. We also 

 estimate the fraction of the potential fecundity deposited 

 by the average female, a key vital rate we approximate 

 by modeling the daily rates of total mortality and egg 

 deposition. Lastly, the term "standing stock of oocytes" is 

 used throughout this article to indicate the total number 

 of oocytes at all stages in an ovary. Whether the standing 

 stock of a particular female is to be considered a potential 



fecundity, a residual fecundity, or something in between, 

 depends upon ancillary information (i.e., presence of post- 

 ovulatory follicles in the ovary, ova in the oviduct, mantle 

 condition, or the level of ovarian maturity). 



Materials and methods 



We collected Loligo opalescens during two southern Cali- 

 fornia research cruises in 1998 (7-15 January and 3-10 

 December) (Fig. 1). Most specimens were taken at night 

 by using trawls, jigging, or by removing them from com- 

 mercial purse-seine catches at sea; some specimens were 

 collected during the day by using bottom trawls. We mea- 

 sured dorsal mantle length (mm), weighed the whole body 

 (g), and classified the ovary and preserved it with viscera 

 and oviduct attached in 10% neutral buffered formalin. 

 To determine reproductive state we decided not to use the 

 familiar ovary classification systems but rather tabulated 

 gross anatomical characters and, later on, selected the 

 most useful characteristics. See Table 1 for characters 

 selected for scoring. 



Preserved ovaries and oviducts were reclassified in the 

 laboratory and weighed (to nearest 0.001 g). A piece of the 

 preserved ovary from each of the 135 female L. opalescens 

 from January and the 117 females from December was 

 sectioned and stained (hematoxylin and eosin). Analyses 

 of the histological sections included identification of the 

 oocytes in the various development stages (I-VI) as de- 

 scribed by Knipe and Beeman (1978), and identification of 

 atresia and postovulatory follicles (Fig. 2 ). We use the term 

 "ova" to indicate an ovulated mature oocyte (stage VI). 



