222 



Fishery Bulletin 103(11 



Dependence of recapture rate on squid size 



Squid tagged off Guaymas ranged from 32.7 to 83 cm ML 

 (mean [±SD] of 56.6 [±7.5] cm ML [Fig. 4]). Recapture 

 rate is clearly size dependent. No squid smaller than 

 46 cm ML were recaptured, and recapture rates were 

 low (1.3-3.4%) for squid of 46-50 cm ML. However, 

 recapture increased in roughly direct proportion to ML, 

 reaching 15-20% for squid >70 cm ML. 



come from the four squid that grew from 47-53 to 71-74 

 cm ML in 207-224 days, and these measurements yield 

 a mean DGR of 1.05 [±0.05] mm/day (Fig. 5 and V in 

 Fig. 6). Solid and dashed curves in Figure 6 represent 

 DGR independently determined for both sexes through 

 analysis of statolith increments (Markaida et al., 2004) 

 for squid of a comparable size range. These growth 

 rates are about twice those determined in the present 

 study by direct ML measurements. 



Determination of daily growth rate (DGR) 



Dorsal ML was measured from forty-four squid tagged 

 off Guaymas after recapture at 4 to 224 days. ML values 

 ranged between 46 and 80.7 cm. Variability in DGR 

 determination, as indicated by the standard devia- 

 tion (SD) of binned data from 20-day intervals, clearly 

 decreased as the time to recapture increased. Thus, a 

 significant negative correlation exists between the SD of 

 DGR and recovery time (r 2 =0.88, P<0.01, n = 6) (Fig. 5). 

 Six measurements of squid caught before 40 days yielded 

 negative growth rates. This finding indicates that large 

 discrepancies in DGR calculations exist in measure- 

 ments on squid with short recapture times, because any 

 errors in ML measurement are generally much larger. 

 Growth rate estimates from squid captured after 40 days 

 yielded values of 1.0-1.5 mm/day (SD of 0.05-0.6). We 

 regard these as the only reliable data. 



Further analysis of DGR was limited to squid cap- 

 tured after 40 days. Figure 6 illustrates DGR versus 

 "mean" ML (average of ML at times of tagging and re- 

 capture) for selected squid of different sexes and stages 

 of maturity. Probably the most reliable DGR estimates 



Tagged off Guaymas n = 995 



Recaptured off Guaymas n = 58 

 Recaptured off Sta Rosalia n=18 

 Recapture rate 



0.20 



- 0.15 



0.10 



0.05 



000 



Discussion 



Tag return rates 



High recovery rates obtained in our study clearly demon- 

 strate that D. gigas in the Gulf of California is suitable 

 for tagging studies. This large species is relatively easily 

 tagged with conventional plastic tags, and the tagging 

 operation produced no obviously deleterious effects on 

 the squid. These features make jumbo squid an attrac- 

 tive species for application of archival electronic tags or 

 telemetry devices. 



Despite extensive tagging efforts and intense com- 

 mercial fisheries, recapture rates for other species of 

 ommastrephid squid have generally been much lower. 

 In the extreme case, no recaptures whatsoever were ob- 

 tained for the northern shortfin squid (lllex illecebrosus) 

 tagged in offshore waters of Newfoundland (Hurley and 

 Dawe, 1981). In other studies recaptures ranged from 

 0.03-0.1% for the Argentine shortfin squid (/. argenti- 

 nus) in the Southwest Atlantic (Brunetti et al., 2000), to 

 1.0-6.2% for the European flying squid (Todarodes sag- 

 ittatus) off Norway (Wiborg et al. 2 ). The neon 

 flying squid iOmmastrephes bartramii) from the 

 North Pacific also yielded low rates (0.1-0.5%; 

 Murata and Nakamura, 1998; see also Nagasa- 

 wa et al., 1993). In 62 years of tagging studies 

 of Japanese flying squid (Todarodes pacificus), 

 only a few experiments carried out in the Sea 

 of Japan and Tsugaru Strait yielded return 

 rates that match those of the present study 

 (up to 16.4%; see Nagasawa et al., 1993). The 

 highest tag recovery rate (19-32%) was found 

 for the northern shortfin squid in Newfound- 

 land inshore areas (Hurley and Dawe, 1981). 

 Recapture rates of up to 12.7% have also been 

 reported for large, neritic loliginid squid (Naga- 

 sawa et al., 1993; Sauer et al., 2000). 



In the present study, recapture rate was 

 found to be directly proportional to mantle 

 length, ranging from <3.5% for squid <50 cm 



ML (cm) at tagging 



Figure 4 



Mantle length (ML) distribution for all squid tagged off Guay- 

 mas (white bars) and for those recaptured off Guaymas (gray 

 bars) and Santa Rosalia (black bars). Black circles represent 

 recapture rate. 



2 Wiborg, K. F., J. Gjosaeter, I. M. Beck, and P. 

 Fossum. 1982. The squid Todarodes sagittatus 

 (Lamarck). Distribution and biology in Northern 

 waters, August 1981-April 1982. Council Meet. Int. 

 Coun. Explor. Sea (K:30):l-17. ICES, Palaegade 

 2-4, DK-1261, Copenhagen K, Denmark. 

 info@ices.dk. 



