NOTE Tanabe and Niu. Sampling juvenile Katsuwonus pelamis and Thunnus spp. 
645 
Table 3 
References for sampling larvae and juvenile skipjack tuna and other tunas. 
Author(s) 
Sampling gear 
Size of sample 
Strasburg, 1960 
1-m ring net 
3-12 mm larvae 
Nishikawa et al., 1978 
2-m ring net and 1.4-m ring net 
<12 mm larvae 
Davis et al., 1990 
0.7-m bongo net and 0.7 ring net 
3-11 mm larvae 
Boehlert and Mundy, 1994 
1-m 2 MOCNESS 
2-8 mm larvae 2 
King and Iversen, 1962 
1-m ring net 
6-ft Isaccs-Kidd trawl 
6-ft Isaacs-Kidd trawl 
10-ft Isaacs-Kidd trawl 
18-60 mm juveniles 
Higgins, 1970 
anchovy no. 2 Cobb pelagic trawl 
7-47 mm larvae and juveniles 
Takuno and Ueyanagi, 1978 
midwater trawl 
6-31 mm larvae and juveniles 
Present study 
midwater trawl 
7.1-171.6 mm larvae, juveniles, 
and young fish 
Thorrold, 1993 
light trap 
10-30 mm juveniles 
‘ Boehlert, G. 1997. Natl. Mar. Fish. 
Serv., NOAA, 1352 Lighthouse Ave., Pacific Grove, CA 93950. Personal 
commun. 
Yoshida (1971) studied the early life history of skip- 
jack tuna using 1742 juveniles collected from the stom- 
achs of billfishes in Hawaiian waters and the central 
South Pacific. Mori (1972) reported on the geographi- 
cal distribution and the relative abundance of juve- 
nile and young skipjack tuna based on collections 
from stomachs of tunas and billfishes in the Pacific, 
Indian, and Atlantic Oceans. This method was con- 
venient and easy for sampling but produced results 
that should be carefully considered because they were 
not based on direct sampling from the habitat. Iizuka 
et al. ( 1989) using pelagic gill nets conducted research 
to collect young skipjack in southern Micronesian wa- 
ters over a period of three years, collecting 49 young 
skipjack, 120 to 280 mm. The research resulted in 
small numbers of specimens of young skipjack tuna, 
and it was not clear whether the number of samples 
indicated the abundance of young stages. 
The results of our study, in light of previous stud- 
ies sampling skipjack tuna and other tunas, show 
that a wider size range of juveniles can be collected 
by using a trawl net with a larger mouth opening 
and by using a high towing speed, as with the Tansyu. 
A small ring net is appropriate for research based on 
sampling larvae because of its simplicity in opera- 
tion. However, if it is necessary that diel patterns of 
vertical distribution of juvenile skipjack and other 
tunas be investigated, then the appropriate time and 
depth of towing should be selected, because ecologi- 
cal characteristics drastically affect the quantity of 
collections. Sampling of young skipjack tuna and 
other tunas, on the other hand, should be conducted 
at night with a trawl net with a large mouth open- 
ing or with a net that would minimize net avoidance 
by young-stage fish. 
Acknowledgments 
This research was funded by the Fisheries Agency of 
Japan with cooperation of the Palau Maritime and 
Micronesian Maritime Authorities. The authors 
thank the crew of RV Tanshu Maru and Omi Maru 
for their assistance in collecting samples. Y. Nishi- 
kawa, S. Cho, and S. Ueyanagi helped identify juve- 
niles of skipjack and tunas and A. Naganuma and Y. 
Watanabe provided many helpful suggestions during 
the period of this research. We thank M. Ogura, K. 
Teshima, and G. Boehlert for reviewing the manuscript. 
Literature cited 
Boehlert, G. W., and B. C. Mundy. 
1994. Vertical and onshore-offshore distributional patterns 
of tuna larvae in relation to physical habitat features. Mar. 
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Davis, T. L. O., G. P. Jenkins, and J. W. Young. 
1990. Diel patterns of vertical distribution in larvae of 
southern bluefin Thunnus maccoyii , and other tuna in the 
East Indian Ocean. Mar. Ecol. Prog. Ser. 59: 63-74. 
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1995. FAO yearbook, fishery statistics, catches and land- 
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United Nations, Rome, 677 p. 
Higgins, B. E. 
1970. Juvenile tunas collected by midwater trawling in 
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Iizuka, K., M. Asano, and A. Naganuma. 
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