FISHERY BULLETIN: VOL. 84, NO. 4 



al. 1983). The stimuli (or stressors) that cause this 

 are unknown. 



Van Heukelem (1979) reviewed environmental fac- 

 tors that influence maturation in cephalopods and 

 reported that light, temperature, and nutrition are 

 the key stimuli. In our experiments, light was con- 

 stant (24 h on), temperature was consistent (ca. 

 15°C) and food was relatively constant and highly 

 available compared with natural populations. How- 

 ever, all three conditions are different from nature. 

 The most interesting result concerns light, which 

 is thought to have a major effect on maturation 

 through the light-optic gland-gonad pathway (cf., 

 Mangold and Froesch 1977; Wells and Wells 1977). 

 Long daylength of high intensity is thought to delay 

 maturation; in our experiments daylength was 24 

 h but intensity (ca. 4-17 lux) was low compared with 

 full sunlight. However, we do not know what light 

 intensity subadult L. opalescens are subject to in 

 nature. Clearly, long daylength alone does not delay 

 maturation in L. opalescens. Future experimenta- 

 tion will be necessary to identify the combinations 

 of environmental factors that affect maturation in 

 the laboratory. 



Life Cycle Comparisons: 

 Laboratory vs. Fishery Data 



In general, five major rearing attempts have been 

 successful in varying degrees: 1) Hurley (1976), to 

 100 d; 2) Hanlon et al. (1979), to 79 d; 3) L.0. 1980, 

 to 233 d and subadult stage (Yang et al, 1980b, 

 1983a); 4) and 5) L.O. 1981 and 1982, to sexual 

 maturity and egg laying within 8 mo (this report). 

 From this it is clear that the life cycle can be <1 yr 

 under laboratory conditions. 



Fields (1965) stated, based upon fishery data, that 

 "Almost all females spawn at the age of 3 

 years...." However, more recent field (cf., 

 Recksiek and Frey 1978) and laboratory studies of 

 L. opalescens (above) indicate that life span 

 estimates beyond 2 years are excessive. Further- 

 more, recent books on cephalopod life cycles (Boyle 

 1983, in press) indicate that few squid live beyond 

 2 years. 



Growth information on laboratory populations is 

 now quite good. The present data allow an accurate 

 assessment by weight from hatching onwards (Fig. 

 9) and firmly verify that young squid are capable 

 of dramatically fast, exponential growth when food 

 is not limiting. This indicates that in nature squid 

 are capable of exploiting plankton blooms and other 

 instances of greater food availability; the highest 

 feeding rates we estimated (29%) also confirm field 



observations that squid will eat large quantities of 

 food when available and when necessary. Field 

 estimates of growth by Fields (1965) and Spratt 

 (1978) are compared with laboratory data in Figure 

 17. Field's data are very conservative (averaging 4 

 mm/month) and based only upon monthly modal 

 length-frequency diagrams from squid on or near 

 spawning grounds. Spratt (1978) estimated growth 

 from statolith rings and hypothesized that growth 

 is rapid during the first few months then decreases 

 with age. Laboratory growth was much faster, but 

 animals were not subject to environmental fluctua- 

 tions. We estimate that growth in nature approx- 

 imates something between the laboratory data and 

 Spratt' s data, and that date of hatching, seasonal 

 temperature fluctuations, and food availability result 

 in life cycle variations between 1 and 2 years. One 

 would expect to observe exponential growth of 

 young squid during spring and summer when tem- 

 peratures and food availability are high, slower 

 logarithmic growth in fall and winter, and spawn- 

 ing the following spring. 



Field evidence (McGowan 1954; Fields 1965) and 

 reproductive physiology studies (Grieb and Beeman 

 1978; Knipe and Beeman 1978) indicate that L. 

 opalescens is a terminal spawner (Hixon 1983), and 

 our laboratory observations verify this since all 

 animals died shortly after spawning (Fig. 13). 



Rings in statoliths may eventually be used as a 

 reliable age marker to determine growth rate and 

 life span. Our preliminary results in this paper from 

 43 statoliths of known age support Spratt's (1978) 

 conclusion that ring deposition occurs roughly on 

 a daily basis during the first 65 d. However, our 

 laboratory data indicate that the relationship does 

 not hold well beyond that age, although Spratt sug- 

 gested that daily ring deposition occurs up to 150 

 d. Thereafter, Spratt (1978) hypothesized lunar 

 (monthly) rings on statoliths but there are no lab- 

 oratory data for comparison. Daily, fortnightly, or 

 monthly growth rings have been hypothesized in the 

 squid Gonatus fabricii (Kristensen 1980), Todarodes 

 sagittatus (Rosenberg et al. 1981), Illex illecebrosus 

 (Hurley and Beck 1980), and Loligoforbesi (Martins 

 1982), but there are no hard data to confirm these 

 estimates. The mechanism of ring formation is 

 unclear but may be related to feeding, since in this 

 part of our laboratory study the squid received food 

 during 12 h and none for the next 12, while concur- 

 rently there was constant light and no temperature 

 fluctuation (Hixon and Villoch 1984). Hurley et al. 

 (1985) and Dawe et al. (1985) found evidence of daily 

 rings in statoliths by inoculating squid with tetra- 

 cycline or strontium. Further work is required to 



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