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Fishery Bulletin 103(1) 



these areas, the average maintained speed during the 

 migration would be about 8 km/day. A comparable fig- 

 ure can be derived from one of our first squid to be 

 recaptured. This animal was tagged at Pt. Prieta (see 

 Fig. 2) and recaptured 20 km away off Sta. Rosalia (Fig. 

 2) after three days. 



This estimated velocity for a trans-Gulf migration is 

 well within the range of rates observed in other studies 

 of ommastrephids (O'Dor, 1988). Jumbo squid tracked 

 with acoustic telemetry off Peru covered 3-5 miles in 

 8-14 hours, or about 14 km/day (Yatsu et al., 1999). 

 Neon flying squid tracked in the same way covered up 

 to 22 km per day (Nakamura, 1993). Migration rates 

 obtained from tagging studies yielded even higher es- 

 timates. Maximum speed for migrating short-finned 

 squid has been estimated at 20-30 km/day (Dawe et al., 

 1981; Hurley and Dawe, 1981), and high rates have also 

 been reported for the Japanese squid (see Nagasawa et 

 al., 1993). Large loliginid squid have been reported to 

 migrate at rates of 3 to 17 km/day (see Sauer et al., 

 2000). 



Daily growth rates 



Variance in DGR estimates from ML measurements 

 decreased dramatically after 30 days after tagging, and 

 became fairly consistent by 50 days. Clearly, estimates of 

 DGR in our study are only reliable for these later times, 

 and a DGR of 1-1.5 mm/day in ML is evident for squid 

 in the 50-70 cm range of ML (Fig. 6). These absolute 

 rates would correspond to relative rates of 0.15-0.22% 

 increase in ML per day. 



There are few comparable estimates of growth rates 

 for other ommastrephid squids based on tag-recapture 

 studies. However, the neon flying squid grows 0.5-2.7 

 mm/day in the 18-48 cm ML range (Araya, 1983), and 

 good agreement exists between growth rates obtained 

 from tag-recapture studies and those from statolith ag- 

 ing studies (Yatsu et al., 1997). When converted to rela- 

 tive growth rate, this species would thus appear to grow 

 substantially faster than the jumbo squid. The common 

 Japanese squid grows 0.45 mm/day (Nagasawa et al., 

 1993), but for this species, mantle lengths were not 

 given; therefore relative rates cannot be estimated. 



More importantly, absolute growth rates determined 

 by direct ML measurements in the present study dis- 

 agreed with those derived from statolith aging methods 

 (Markaida et al., 2004), and this discrepancy merits 

 re-evaluation of previous longevity estimates. Squid of 

 50 cm ML are thought to be about 260 days old based 

 on statolith ring counts, and our tag-recapture study 

 revealed that it can take another 200 days to grow to 70 

 cm ML. The estimated age at this size would therefore 

 be 460 days, about 100 days more than that estimated 

 by statolith aging for squid of 70 cm ML (Markaida et 

 al., 2004). Thus, the largest squid found in the Gulf of 

 California (about 90 cm ML) might be up to 2 years 

 old. 



Reasons for the apparent underestimates in longevity 

 with statolith aging are unclear. Difficulty in resolving 



discrete rings late in life of a specimen is one possibil- 

 ity. Another is that the assumed daily ring deposition 

 may not occur throughout the lifetime of a jumbo squid. 

 No successful validation studies have been reported for 

 this species, either in the laboratory or in the wild. 



Squid distributions in the Gulf in relation 

 to commercial landings 



Although large-scale migrations of jumbo squid within 

 the Guaymas basin are apparently responsible for the 

 seasonal pattern in the commercial landings (Fig. 1; see 

 also Markaida and Sosa-Nishizaki, 2001), the biological 

 and oceanographic reasons for these migrations are not 

 well established. The reciprocal pattern in squid distri- 

 bution between the eastern and western central Gulf is 

 correlated with the wind-driven upwelling seasonality 

 in this area (Roden and Groves, 1959) and is probably 

 highly influenced by this oceanographic feature. A simi- 

 lar situation exists in the life cycle of another important 

 pelagic resource, the Pacific sardine (Sardinops caeru- 

 leus) (Hammann et al., 1988). 



However, other biological factors are also probably 

 important. Summer upwelling in the western Gulf is 

 actually less intense than off the eastern coast in win- 

 ter (Hammann et al., 1988; Santamaria-del-Angel et 

 al., 1999), yet 80% of squid landings were made at Sta. 

 Rosalia between 1995 and 1997 (Markaida and Sosa- 

 Nishizaki, 2001). We propose that concentrations of 

 spawning myctophids (lanternfishes) off Baja California 

 in the summer (Moser et al., 1974) may be largely re- 

 sponsible for this disparity because these fish are a ma- 

 jor prey item for squid in the Guaymas basin (Markaida 

 and Sosa-Nishizaki, 2003). 



Data in the present study also indicate that jumbo 

 squid may be available to commercial fishing efforts off 

 each coast for a longer period than previously thought. 

 Our data indicate that squid were recovered in the 

 waters off Guaymas throughout the year; therefore it 

 is likely that some squid do not undergo the westward 

 spring migration (Fig. 3B). However, it is not certain 

 that the final returns from Guaymas after 7 months 

 were of this resident stock, because they would have 

 had time to migrate to Sta. Rosalia and back again. It 

 is also unclear whether a resident stock of squid exists 

 in the Sta. Rosalia area year-round. Strong northern 

 winds in this area lead to a cessation of commercial 

 fishing efforts during the winter months, and the lack 

 of tag returns during winter may simply reflect this 

 fact. 



Long-distance migrations into and out of 

 the Gulf of California 



Although data in this paper have demonstrated seasonal 

 migrations of jumbo squid within the Guaymas basin, 

 migration patterns into this region from the southern 

 Gulf and open Pacific (and back out) remain unknown. 

 The much lower level of commercial fishing effort in 

 these latter areas will greatly constrain efforts to elu- 



