408 
Fishery Bulletin 106(4) 
Table 1 
Species composition of tuna larvae (family Scombridae) caught during four cruises in the Coral Sea, near the Great Barrier 
Reef, between November 1984 and February 1985. Values are numbers of larvae caught. Taxa are ordered to allow comparison 
of larval numbers among groups comprising the same genera. 
Taxon 
Early 
November 
cruise 
Late 
November 
cruise 
Early 
February 
cruise 
Late 
February 
cruise 
Species 
total 
Proportion 
of total catch 
(%) 
Katsuwonus pelamis 
55 
89 
109 
94 
347 
34 
Thunnus spp. 
3 
24 
116 
29 
172 
17 
Thunnus albacares 
11 
19 
49 
16 
95 
9 
Thunnus alalunga 
69 
62 
26 
14 
171 
17 
Auxis-Euthynnus 
13 
2 
72 
9 
96 
10 
Euthynnus affinis 
49 
4 
54 
1 
108 
11 
Auxis spp. 
5 
0 
10 
7 
22 
2 
Total 
205 
200 
436 
170 
1011 
priately scaled values. Abundance values incorporate 
a depth component, and are therefore appropriate for 
comparing oblique samples taken down to different 
depths. Statistical analyses of on-offshore patterns of 
distribution of tuna larvae were performed on natu- 
ral log-transformed abundances, following inspection 
of the data for normality and heterogeneity of vari- 
ance. A count of 1 was added to all data-points before 
transformation, to allow transformation of zero values. 
Preflexion and postflexion larvae were combined for 
on-offshore analyses. For each taxon, analysis was 
done only for cruises with an average larval abundance 
>1 larvae/100 m 2 to avoid problems associated with 
numerous zeros. Lagoon samples were not included in 
calculation of the cruise average because few larvae 
of any tuna taxon were caught in the lagoon. Only K. 
pelamis larvae were sufficiently abundant for analysis 
on all four cruises, and their abundance among on- 
offshore blocks (including the lagoon) and cruises was 
compared by using a two-factor analysis of variance 
(ANOVA). For other taxa, abundance among blocks 
was analyzed with a one-factor ANOVA for each cruise 
with larval abundance >1 larvae/100m 2 . When ANOVA 
tests yielded significant (P<0.05) results, pairwise dif- 
ferences between blocks were analyzed using Tukey’s 
test. Auxis spp. larvae were not sufficiently abundant 
on any cruise to allow for statistical analysis. 
Size-frequency data from blocks A and B (inshore 
zone, 0-1.85 km from the reef) were pooled and com- 
pared with size-frequency data pooled from blocks C 
and E (offshore zone, >1.85 km from the reef) using 
the Kolmogorov-Smirnov (K-S) test. Data were pooled 
to increase n , because few taxa had sufficient numbers 
of larvae in each block to provide adequate statistical 
power. K-S tests were done on data from individual 
cruises. Larvae from the lagoon were excluded from 
size-frequency analysis because of low abundance. The 
significance level used for all statistical tests was 0.05. 
Not enough E. affinis larvae were caught in both zones 
on any cruise to allow a statistical comparison of size 
distributions. 
Results 
Species composition and abundance 
Over 1000 tuna larvae were caught, comprising at least 
five species and four genera (Table 1). Larvae of K. 
pelamis were the most abundant, making up over one 
third of all tuna larvae caught. Numerous small (<3.2 
mm SL) Thunnus spp. larvae were caught on the early 
February cruise, coinciding with a peak in abundance 
of less common T. albacares larvae. In contrast, T. 
alalunga larvae were most abundant on the November 
cruises, and only 26 individuals were caught on the 
early February cruise. It is, therefore, likely that most 
of the Thunnus spp. larvae were T. albacares. Larvae of 
other Thunnus species (e.g., T. obesus [bigeye tuna] or 
T. tonggol llongtail tuna]) were not caught and would 
have been distinguishable from T. albacares and T. 
alalunga, even at small (<3.2 mm SL) sizes (Fritzsche, 
1978). Euthynnus affinis larvae were most common on 
the early November and early February cruises, and 
Auxis-Euthynnus larvae were most abundant on the 
early February cruise. Only 22 Auxis spp. larvae were 
caught during the study, therefore Auxis-Euthynnus 
larvae were most likely primarily E. affinis larvae. 
On-offshore distribution 
Tuna larvae generally had near-reef distributions, as 
greatest abundances usually occurred within 5.6 km of 
the outer reefs of the Great Barrier Reef in the Coral 
Sea. Patterns of on-offshore distribution differed among 
taxa, however. 
Species of Thunnus had the most consistent near- 
reef distribution among the taxa of tuna larvae, with 
