Fishery Bulletin 105(1) 



1995). Physical data were compared between collection 

 group periods using ANOVA and the SNK test. 



Results 



Collections and identification 



The occurrence of fairly large numbers (approximately 

 100 or more) of larval and early-stage juvenile Thun- 

 nus was sporadic, but not uncommon, in night-light 

 collections during certain months of each year of the 

 reduced upwelling season (Table 1). Based on back- 

 calculated spawning dates and the average surface 

 current speed, the collection site within an 8-degree 

 latitude by 8-degree longitude area (between 2-10°N and 

 77-85°W) was estimated as the average maximum area 

 potentially occupied by yellowfin tuna larvae of each 

 collection group during their early life history (Table 2, 

 Fig. 2). At the time of collection, sizes of larvae ranged 

 from 6.2 to 19.6 mm SL (Table 1), and all were either 

 in the flexion, postflexion, or transformation stages of 

 development (stages described in Ambrose, 1996). Other 



scombrid species (\.e.,Auxis sp., Euthynnus lineatus, and 

 Scomberomorous sierra) were also found when Thunnus 

 larvae were collected, but were not usually predominant 

 in the collections. 



Successful PCR amplification occurred in 80% of the 

 larvae analyzed, and subsequent RFLP analysis in- 

 dicated that the Thunnus larvae collected near the 

 Frailes Islands were T. albacares (Table 1). 



Size-at-age and growth 



The ages of yellowfin tuna larvae collected ranged from 

 8 to 20 days (Table 1, Fig. 3). The age range was mostly 

 limited between 11 and 14 days for the larvae collected 

 in July 1991 (collection group II) and in June- July 1992 

 (collection group IV); therefore growth models were not 

 fitted to the data (Figs. 3 and 4). However, a comparison 

 of the size-at-age between all five groups within this lim- 

 ited age range indicated that both SLs and otoliths were 

 significantly smaller for larvae collected in September 

 1991 (collection group III) (ANCOVA and Tukey multiple 

 comparison test, P<0.0001), and that SLs were similar 

 between the larvae of 1990 (collection group I) and July 



