Abstract — Tuna larvae (at flexion, 

 postflexion, and transformation 

 stages) were collected by dip net and 

 light traps at night in the northwest- 

 ern Panama Bight during the season of 

 reduced upwelling (June-September) 

 of 1990, 1991, 1992, and 1997. The 

 larvae were identified as yellowfin 

 tuna {Thunnus alhacares) by mtDNA 

 analysis. Ichthyoplankton data from 

 bongo and Tucker trawl tows were 

 used to examine the potential prey 

 abundance in relation to the mean 

 size-at-age and growth rates of the 

 yellowfin tuna larvae and their oto- 

 liths. The most rapid growth rates 

 occurred during June 1990 when 

 plankton volumes were at their 

 highest levels. The lowest plankton 

 volumes coincided with the lowest 

 growth rates and mean sizes-at-age 

 during the August-September 1991 

 period. High densities of larval fish 

 were prevalent in the ichthyoplankton 

 tows during the 1991 period; therefore 

 intra- and interspecific competition 

 for limited food resources may have 

 been the cause of slower growth (den- 

 sity-dependent growth) in yellowfin 

 tuna larvae The highest mean sea- 

 surface temperature and the lowest 

 mean wind stress occurred during an 

 El Nino-Southern Oscillation (ENSO) 

 event during the 1997 period. There 

 appeared to be no clear association 

 between these environmental fac- 

 tors and larval growth rates, but 

 the higher temperatures may have 

 caused an increase in the short-term 

 growth of otoliths in relation to larval 

 fish size. 



Temporal variation in growth of yellowfin tuna 

 iThunnus aibacares) larvae in the Panama Bight, 

 1990-97 



Jeanne B. Wexler (contact author)' 



Seinen Chow^ 



Toshie WakabayashP 



Kenji Nohara^ 



Daniel Margulies' 



Email address for J. B, Wexler: iwexler@iattc.org 



' Inter-Amencan Tropical Tuna Commission 



8604 La Jolla Stiores Drive 



La Jolla, California 92037-1508 

 2 National Research! Institute of Fisheries Science Nagai 



6-31-1 Yokosuka 



Kanagawa 283-0316 Japan 

 ^ National Research Institute of Far Seas Fisheries 



5-7-1 Shimizu-Orido 



Shizuoka 424-8633 Japan 



Manuscript submitted 22 October 2004 

 to the Scientific Editor's Office. 



Manuscript accepted 14 March 2006 

 by the Scientific Editor. 



Fish. Bull. 105:1-18 (2007). 



Yellowfin tuna iThunnus aibacares) 

 larvae inhabit the mixed layer of all 

 tropical and subtropical oceans of the 

 world (Ueyanagi, 1969; Nishikawa et 

 al., 1985). When recruited to the com- 

 mercial fishery, yellowfin tuna are one 

 of the most important tuna species 

 worldwide (Collette and Nauen, 1983; 

 FAO, 2004). Near-daily spawning of 

 yellowfin tuna, and the subsequent 

 dispersal of fertilized eggs, appears 

 to be largely dependent on the occur- 

 rence of surface water temperatures 

 equal to or greater than 24°C (Schae- 

 fer, 1998). In the eastern Pacific 

 Ocean (EPO), yellowfin tuna spawn 

 continuously between 0° and 20°N 

 (Schaefer, 20011. Despite widespread 

 spawning of yellowfin tuna through- 

 out the EPO, the larvae are patchy 

 in distribution (Ahlstrom, 1971), and 

 relatively large numbers have been 

 collected only near islands (Graves et 

 al., 1988; this study) and near shore 

 (Gonzalez Armas, 2002). 



The larvae of Thunnus are difficult 

 to identify by meristic, morphological, 

 or pigmentation characteristics (Mat- 

 sumoto et al., 1972; Potthoff, 1974; 

 Richards et al., 1990; Lang et al., 

 1994). In the EPO, the late-larval and 

 early-juvenile stages of yellowfin and 

 bigeye (T. obesus) tuna co-exist and 

 cannot be differentiated by these con- 



ventional methods. However, allozyme 

 (Graves, et al., 1988) and recent mo- 

 lecular (Takeyama et al., 2001; Chow 

 et al., 2003) analyses have made it 

 feasible to identify larvae of these two 

 species that inhabit the EPO. 



The growth dynamics of yellowfin 

 tuna during early life stages may 

 have a profound effect on cohort 

 strength (Houde, 1987), but growth 

 rates have not been described for the 

 larvae in the Pacific Ocean. Larval 

 and juvenile stage durations and 

 corresponding growth rates (Houde, 

 1989), starvation rates (Margulies, 

 1993), and larval transport and pre- 

 dation (Grimes, 2001) may be strongly 

 influenced by biological and physical 

 processes that would affect prerecruit 

 survival in yellowfin tuna. Standing 

 stocks of phytoplankton and zoo- 

 plankton in the EPO, where yellow- 

 fin tuna larvae are found are season- 

 ally variable (Blackburn et al., 1970; 

 Owen and Zeitschel, 1970; Lauth and 

 Olson, 1996; Gonzalez Armas, 2002) 

 and influenced by interannual events 

 such as El Nino-Southern Oscilla- 

 tion (ENSO) conditions (Dessier and 

 Donguy, 1987; Fiedler, 1992; Chavez 

 et al., 1999; Strutton and Chavez, 

 2000). In the northwestern Panama 

 Bight of the EPO, nearshore ichthyo- 

 plankton surveys (from 1989 to 1993) 



