NOTE Markaida et al .: Tagging studies on Dosidicus gigas 



223 



ML to 20% for squid close to 80 cm ML (Fig. 

 4). Reasons for this strong size-dependence 

 are not clear. Smaller squid may either suffer 

 a higher natural mortality rate or migrate 

 southward out of the Guaymas basin more 

 readily than the larger squid. We do not be- 

 lieve that the tagging process itself leads to 

 such a difference in mortality rate, but this 

 possibility cannot be ruled out. 



Several factors are relevant to evaluating 

 differences in recapture rates for jumbo squid 

 and other ommastrephids. First, squid of the 

 other species are not as large as jumbo squid. 

 We are not aware of any other published data 

 on size-dependence of recapture rates, but 

 this phenomenon may be relevant. Second, 

 the localized nature of the fisheries surround- 

 ing the Guaymas basin equates with high 

 concentrations of squid in relatively small ar- 

 eas that are intensively fished. Most recent 

 tagging studies of other ommastrephids have 

 taken place in oceanic waters in the Sea of 

 Japan and North Pacific, where the fishing 

 zone is extremely large and far from any lo- 

 calized coastal fishing areas (Nagasawa et 

 al, 1993). The extreme disparity in return 

 rates for nearshore versus offshore studies 

 in Newfoundland supports this idea. Third, 

 an ambitious advertising campaign (posters) 

 and the substantial reward offered for tag 

 returns undoubtedly stimulated a high degree 

 of cooperation in the largely artisanal Mexi- 

 can fishery that is highly concentrated in Sta. 

 Rosalia and Guaymas. A strong dependence 

 of tag-return rate on rewards and advertis- 

 ing has been previously noted (see Nagasawa 

 et al., 1993). 



Seasonal migration 



Results from this study directly demonstrate 

 that jumbo squid in the Guaymas basin 

 migrate across the Gulf on a seasonal basis. 

 Squid appear to migrate from Sta. Rosalia to 

 Guaymas during the second half of November 

 and early December and to make the reverse 

 trip in late May and early June. Thus, large 

 squid (40-80 cm ML) remain available to fish- 

 eries surrounding the Guaymas basin through- 

 out the year. These data support the idea 

 that these fishing areas are feeding grounds 

 (Markaida and Sosa-Nishizaki, 2001). What 

 fraction of squid, if any, migrate southward out 

 of the Guaymas basin and potentially into the 

 Pacific cannot be ascertained from our data. 



Transit time across the Gulf for the migrat- 

 ing squid appears to be fairly brief — proba- 

 bly less than 16 days based on the overlap of 

 recaptures in both fishing areas. Assuming 

 a straight-line distance of 130 km between 



CO 1 



XI ' 



E 



E 



DC 

 O 



a 



• . • *T 



• 6 * 



□ • • 



-- 



-2 



-3 -I 



10 20 30 40 50 60 70 80 90 100 210 220 

 Days elapsed between tagging and recapturing 



Figure 5 



Daily growth rate (DGR) in mantle length (ML) determined for 

 squid recaptured at different times after tagging. Black circles 

 represent measurements from individual animals. Gray squares 

 represent means ±1 SD for squid grouped in 20-day bins. Note 

 that a gap exists between 100 and 200 days. 



v Recaptured after 200 days 

 o Immature Female 

 • Mature Female 



Maturing Male 



Mature Male 



Mean ±SD for each 5-cm ML bin 



Females (Markaida et al.. 2003) 



Males 



ra 2.0 



E 

 E 



rr 

 a 



60 65 70 



Mean ML (cm) 



80 



Figure 6 



Relationship of daily growth rate (DGR) and mean mantle length (ML) 

 (average of measured ML at time of tagging and time of recapture). 

 Small symbols represent measurements from selected individual 

 animals as follows: squid recaptured after >200 days (V), immature 

 female (Ol, mature female (•), maturing male (A), mature male (A). 

 Larger squares (■) indicate means ±1 SD for all data pooled into 

 5-cm bins. Analysis was limited to squid recaptured after 40 days 

 and of identified sex. Curves represent DGR vs. ML relationship 

 as determined by counting statolith increments for females (solid) 

 and males (dashed) and are adapted from Markaida et al. (2004). 



