Schaefer: Assessment of spawning activity of Katsuwonus pelcimis in the eastern Pacific Ocean 
349 
portunistic nature of this species, assessments should nev- 
ertheless be conducted for the skipjack tuna stock within 
this geographical region. Ideally, stock assessment models 
for skipjack tuna should incorporate spatial and temporal 
variability in the size-specific parameters for age, growth, 
movement, mortality, and reproduction. A more compre- 
hensive investigation of the reproductive biology of skip- 
jack tuna in the EPO is in progress. 
Acknowledgments 
I gratefully acknowledge the previous Director of IATTC, 
Jim Joseph, the present Director, Robin Allen, and Chief 
Scientist of the Tuna-Billfish Program, Rick Deriso, for 
their encouragement and support of this investigation. I 
thank numerous members of the IATTC staff, particularly 
those stationed at field offices, whose assistance in sam- 
pling skipjack specimens for this project was invaluable. I 
also wish to thank Bill Bayliff and two anonymous review- 
ers for constructive comments on drafts of the manuscript. 
A 
93 
lllllh..^ 
. m 
Miiiiiii. _r 
jA 
95 
hill. 
: ..mu 
96 
IIMul 
i\ 
97 
lIllilEli. = 
jk 
98 
lllllllll... 
20 30 40 50 60 70 80 
Length in centimeters 
90 
Figure 7 
Estimated length compositions of the total skipjack tuna 
catch, by 2-cm intervals, in the eastern Pacific Ocean. These 
histograms are based on the catch statistics and length- 
frequency samples of skipjack tuna, for each year of the 
1993-98 period, compiled by the Inter-American Tropical 
Tuna Commission. 
Literature cited 
Ahlstrom, E. H. 
1971. Kinds and abundance of fish larvae in the eastern 
tropical Pacific, based on collections made on EASTROPAC 
I. Fish. Bull. 69( 1 ):3-77. 
1972. Kinds and abundance of fish larvae in the eastern 
tropical Pacific based on the second multivessel EASTRO- 
PAC survey, and observations on the annual cycle of larval 
abundance. Fish. Bull. 70(41:1153—1242. 
A1 verson, F G. 
1960. Distribution of fishing effort and resulting tuna 
catches from the eastern tropical Pacific Ocean by quar- 
ters of the year, 1951-1958. Inter-Am. Trop. Tuna Comm.. 
Bull. 4(61:319-446. 
1963. Distribution of fishing effort and resulting tuna 
catches from the eastern tropical Pacific Ocean, by quar- 
ters of the year, 1959-1962. Inter-Am. Trop. Tuna Comm., 
Bull. 8(61:317—379. 
