324 



Fishery Bulletin 102(2) 



is the daily natural mortality of the spawners?" Loligo 

 opalescens have only one spawning period in their life 

 time (McGowan, 1954; Fields, 1965; Butler et al., 1999) 

 but how long that period lasts remains unknown. Melo 

 and Sauer (1999) concluded that the spawning period of 

 L. v. reynaudii consisted of more than one spawning bout 

 but neither the number of bouts nor the duration of each 

 spawning period is known. In a laboratory study of L. 

 pealeii (Maxwell and Hanlon, 2000), the number of bouts 

 varied from one to ten, the interval between bouts was 

 highly variable, and the life span after the first spawn- 

 ing bout was from 3 to 50 days. Our best guess for L. 

 opalescens under fishing conditions was an average life on 

 the spawning grounds of only 1.67 days and a maximum 

 longevity of about 6 days. These estimates were based on a 

 simple exponential model, constrained by various proxies 

 for egg deposition rate, longevity, and the fraction of the 

 potential fecundity in the catch (the only directly mea- 

 sured value). We believe that two of our estimates, 36% of 

 the potential fecundity is deposited in the first 24 hours of 

 spawning and minimum residual fecundity is about 22% 

 of the potential fecundity, are on relatively firm ground 

 but our estimate of the maximum longevity on the spawn- 

 ing grounds as 6 days is speculative. New information on 

 mortality is needed because, over a wide range of daily 

 mortality rates, our model yields values that are consis- 

 tent with observed average fraction of potential fecundity 

 in the catch. Because direct measurement of mortality on 

 the spawning grounds may be difficult, it may be useful 

 to develop some indirect approaches. For example, a lab- 

 oratory study could be designed to generate an energy- 

 based model that converts squid mantle tissue loss to 

 deposited eggs. This mantle-to-egg conversion rate could 

 be used to assign an age (time elapsed after first egg depo- 

 sition) to modes of mantle condition from fishery samples. 

 Mortality could then be computed by following modes of 

 mantle condition through time. 



Acknowledgments 



This study was a cooperative project between the Cali- 

 fornia Department of Fish & Game (CDF&G) and the 

 National Marine Fisheries Service (NMFS) from start 

 to finish. We worked closely with CDF&G personnel 

 throughout the study with port-sampling data, cruise time, 

 and partial financial support was provided by CDF&G. 

 We worked particularly closely with M. Yaremko, A. 

 Henry, and D. Hanan of CDF&G. J. Welsh assisted in 

 the fecundity work. Others that contributed include J. 

 Butler, T. Kudroschoff, N. Smith, A. Preti, K. Lazar, 

 A. Cossio, and at sea K. Barsky, T. Bishop, S Charter, 

 R. Dotson, D. Fuller, C. Graff, D. Griffith, P. Hamdorf, 

 A. Hays, B. Horandy, M. Levy, I. Taniguchi, J. Ugoretz, and 

 L. Zeidberg. We wish to thank the crews of the research 

 vessels Jordan and Mako. We especially wish to thank diver 

 J. Hyde who observed, collected, and photographed squid in 

 La Jolla Canyon. M. Maxwell and two anonymous review- 

 ers read the manuscript and provided constructive com- 

 ments. R. Allen and H. Orr improved our illustrations. 



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