390 



Fishery Bulletin 102(2) 



No Maling Squids 



Mating Squids Present 



29Apr00-, 

 30Apr00 



n i May Uli 

 04May00 

 OSMayOO 

 OtSMayOO 

 07May00 



•Wk 



^mmm-M 



Sunset 



b mw?. 



wmmmmr* 



lOSepOO 

 12Sep00 

 USepOO 

 16SepOO 



0000 0200 0400 0600 0800 1000 1200 1400 



Time of day (h) 



1600 1800 2000 2200 2400 



Figure 1 



A summary of 154 spawning groups of Lot igo opalescens showing the daily presence or 

 absence of mating squids on egg beds in Monterey Bay, California. The horizontal bars repre- 

 sent the time periods when a ROV was on the bottom searching for mating squids during three 

 different expeditions. Note three occasions in which operations were conducted continuously 

 through the day and night, and also that spawning ceased at dusk. 



laying frequency (Hanlon et al., in press). Only very rarely 

 did we observe females laying eggs while unattended by a 

 male; in these cases the female was moribund and laying 

 her last few egg strands. 



Results and discussion 



We examined 28 hours of videotape recorded during 50 

 ROV dives over 18 days (divided into three expeditions). 

 Figure 1 illustrates the relative presence or absence of 

 mating Lo//go opalescens throughout 24-hour periods. The 

 large gaps in the daytime observation record were due to 

 ROV problems. Although observation times varied daily, 

 it is clear that normal mating and egg-laying behaviors 

 were exclusively observed during daylight hours (ca. 

 0800-1800 hours but with some seasonal variation) and 

 concluded near dusk. In all instances in Figure 1 where 

 egg-laying extended into the early evening, these mating 

 assemblages had formed during daylight hours and per- 

 sisted slightly past sunset and the number of participating 

 squids constantly decreased as sunset approached and 

 passed. Observations were made throughout the night 

 on three nights. Not only were no mating squids ever 

 encountered around the egg beds at night, but generally 

 no squids were encountered at all near the seabed, despite 

 large aggregations that were present higher in the water 

 column. Thus the 200-400 watt lights on the ROVs never 



induced any artificial spawning behavior because there 

 were no squids present. 



Figure 2 provides some quantification of Figure 1. This 

 graph is based on 154 spawning groups that were vid- 

 eotaped and includes all three trips as well as the three 

 "all night observations" illustrated in Figure 1. We were 

 studying discrete groups of squids to examine mating dy- 

 namics and thus were sometimes biased to smaller groups 

 of squids that could be kept in view. Overall, we observed 

 that squids were present in greatest numbers in mid to 

 late afternoon and absent during the night. 



Our findings strongly indicate that the extensive egg 

 beds produced at depths of 20-60 m in southern Monterey 

 Bay (just beyond the kelp beds) are the result of daytime 

 aggregations of mating Loligo opalescens. These benthic 

 aggregations begin forming in the early morning hours 

 and tend to be larger in the afternoon. Reproductive ac- 

 tivity begins to wane toward sunset and comes to a near 

 halt at sunset. We could find no evidence that egg laying 

 occurs naturally during the night. All observations that 

 we are aware of (mainly television documentaries) have 

 occurred in the presence of artificial light sources near the 

 surface provided either by fishermen or cinematographers. 

 In the absence of artificial lighting, L. opalescens in South 

 Monterey Bay does not aggregate into mating and spawn- 

 ing groups at night. Thus, we conclude that all significant 

 egg deposition in the Monterey Bay fishery is the result of 

 daytime aggregations of squids. 



