216 
Fishery Bulletin 96(2), 1998 
sets by the U.S. fleet from 595 to 2,190 short tons 
per year. Redistributing all dolphin sets to log sets 
had by far the greatest effect, increasing predicted 
annual discard of tuna from log sets by the U.S. fleet 
from 5,400 to 19,900 short tons. 
Predicted total annual discards of tuna from the 
U.S. fleet for all set types combined were 7,500, 
14,000, and 20,500 short tons for redistribution of 
dolphin sets to all school sets, combined school and 
log sets, and all log sets, respectively (Fig. 5), repre- 
senting increases of 1.25 (7,580/6,080), 2.31 (14,000/ 
6,080), and 3.34 (20,500/6,080) times, respectively. 
Discussion 
Comparison with other discard data 
Although the data used in this report consist of esti- 
mates made “by eye” (i.e. estimated by visually not- 
ing the volume of discarded tuna 
and mentally comparing that vol- 
ume to the volume of tuna in some 
container of known size, e.g. the 
vessel’s brailer) and could not be 
analyzed in hindsight for inter-ob- 
server reliability, our results are 
reasonably similar in magnitude, 
especially in relative magnitude (ex- 
pressed as tonnages) between set 
types, to data collected during 1993 
and 1994 by the IATTC as part of a 
greatly expanded bycatch sampling 
program in the ETP. Average short 
tons of tuna discarded per set dur- 
ing these 2 years for dolphin, school, 
and log sets was 0.17 (no difference 
between years), 0.58 (0.5 in 1993, 0.9 
in 1994), and 8.3 (5 in 1993, 11 in 
1994), respectively (Hall 8 ). These 
values are reasonably comparable to 
our estimates of 0.06, 1.2, and 10.5 
short tons of tuna discard per set for 
dolphin, school, and log sets, respec- 
tively. The apparently large differ- 
ences between the IATTC and 
NMFS estimates for dolphin sets, 
and to some extent for school sets, 
are relatively unimportant because 
the overall discards for these set 
types are so low. In addition, annual 
differences can be substantial al- 
though still low in relation to log 
sets. 
Implications for the ETP 
yeHowfin fishery 
o 
CD 
O 
CNJ 
O 
CO 
o 
C\J 
o 
o 
o 
in 
Dolphin sets 
ll. 
10 
20 
30 
40 
50 
School sets 
20 
30 
40 
Log sets 
50 
liiliiiiLi.j 
l__B 
10 
20 
30 
40 
50 
Observed bycatch (short tons) 
Figure 3 
Frequency distributions of observed discard per set for dolphin, school, and log 
sets by the U.S. tuna purse-seine fleet fishing in the eastern tropical Pacific 
Ocean, 1989-92. The scale for school sets does not show 3 school sets exceeding 
50 short tons per set, totaling 310 short tons, and representing 30% of total 
catch on school sets, with maximum catch per school set = 150 short tons. The 
scale for log sets does not show 25 sets exceeding 50 tons per set, totaling 3,221 
short tons, and representing 33% of the total catch on log sets, with maximum 
catch per log set = 325 short tons. 
Our results imply that historically, 
tuna discard from the U.S. tuna 
Hall.M. 1995. Inter- American Tropical 
Tuna Commission, c/o Scripps Institute of 
Oceanography, La Jolla, CA 92038. Per- 
sonal commun. 
