Wexler et al.: Temporal variation in larval growth of Thunnus olbocares in the Panama Bight 



30' 



yN - 



1993) deployed near the surface. All larvae 

 were fixed in 95% ethyl alcohol shortly after 

 capture, except for some that were caught 

 alive and used in laboratory experiments. 

 Fish used in laboratory experiments were 

 not used for the age and growth analyses. 

 SSTs were recorded with a bucket ther- 

 mometer, and the salinity of a sample of 

 water taken just below the surface was 

 measured with a handheld salinometer. 

 Visual observations of environmental con- 

 ditions (e.g., wind, currents, and weather) 

 were recorded at the time of sampling. 



Laboratory procedures and analyses 



Larvae of the genus Thunnus were sorted 

 from other scombrid larvae by the morpho- 

 logical features and meristics described in 

 Nishikawa and Rimmer (1987) and Ambrose 

 (1996). The standard length (SL) of each 

 larva was measured in distilled water before 

 the sagittal otoliths were removed for aging 

 and before the remaining tissue of each 

 individual was placed in 95% ethyl alco- 

 hol for species identification. The sagittae 

 were removed, cleaned of tissue with chlo- 

 rine bleach, rinsed in distilled water, dried, 

 and embedded distal side up with Eukitt 

 (O. Kindler, Freiberg, Germany) mount- 

 ing medium on a glass slide. The diameter 

 along the longest axis of each sagitta was 

 measured with an ocular micrometer and 

 light microscope. The sagittae were pol- 

 ished at the surface until the increments 

 were clearly visible with transmitted light 

 at a magnification of 480 or 720x. Daily 

 increments (previously validated in Wexler 

 et al., 2001) of the left and right sagittae 

 were counted "blindly" (i.e., repeated counts 

 were made without prior knowledge of the 

 previous counts) by the first author until the 

 same number of increments were counted 

 at least three times in one of the sagittae. 

 The number of increments in the sagitta 

 that was more clearly read (which usually 

 resulted in a higher count) was used as a 

 direct estimate of age for that fish. 



The temporal variation in growth was examined by 

 comparing the size-at-age data of the larvae and their 

 otoliths among collection periods through analysis of 

 covariance (ANCOVA) and a multiple range comparison 

 test (Tukey HSD) (XLSTAT vers. 7.5.2, Addinsoft USA, 

 New York, NY) (a=0.05). 



DNA analysis and species identification 



The flanking region between ATPase 6 and cytochrome 

 oxidase subunit I (COI) genes of mtDNA was ampli- 

 fied by using the polymerase chain reaction (PCR), 



20' 



80° W 



I'N 



20' 80°W 



Figure 1 



Locations where yellowfin tuna iThunnus albacares) larvae were col- 

 lected with an underwater light at night (cross hatched; from 1990-92 

 and 1997) and where ichthyoplankton sampling occurred (during 

 1990-92) near the Achotines Laboratory, on the Azuero Peninsula of 

 the northwestern Panama Bight. Ichthyoplankton sampling stations 

 along the Punta Mala and Morro Puercos transects are the following: 

 Mala abyss (MAB), Mala slope (MSL), Mala shelf break (MSB), Mala 

 shelf iMSH), Puercos abyss (PAB), Puercos slope (PSL), Puercos shelf 

 break (PSB), Puercos shelf (PSHJ. 



and restriction fragment length polymorphism (RFLP) 

 patterns were used to identify the species of Thunnus 

 larvae according to protocols of Takeyama et al. (2001) 

 and Chow et al. (2003). Albacore (T. alalunga), yellowfin, 

 and bigeye tunas in the Pacific Ocean can be identified 

 by the diagnostic restriction profile of Mse I digestion 

 (Chow and Inoue, 1993), and this enzyme assay was used 

 to identify the species of larvae collected in 1990-92. 

 Chow et al. (2000) found, however, that many specimens 

 of bigeye tuna in the Atlantic Ocean shared the same 

 restriction profile with yellowfin tuna; this also occurred 

 in the Pacific Ocean, but at a much lower frequency 

 (1 out of 144 individuals examined). Takeyama et al. 



