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Fishery Bulletin 111(2) 
were made in the area of lower catch probabilities; 
however, some were from the boundary regions of high 
probability in the offshore waters of Java. Predictions 
of higher catch probabilities of Bigeye Tuna catches 
appeared to be associated with frontal areas in 10- 
12°S, a region that seemed to reveal the importance 
of the confluence on the eastward IOKW and SJC that 
met with the outflow of the ITF and SEC in the off- 
shore area of the EIO off southern Java. 
There were many potential fishing locations that 
were not used optimally, and this inefficient use re- 
duced the total catch to much less than the level that 
was expected during the El Nino 1997-98 year. None- 
theless, the catch remained significantly higher during 
this El Nino event than during the 1999-2000 La Nina 
event. The mismatch between optimal fishing locations 
and actual fishing locations can be attributed to one or 
more of the reasons outlined below: 
The fishermen did not have the capability to deter- 
mine potential Bigeye Tuna habitats on the basis of 
large-scale regional shifts in oceanographic and climate 
regimes. They still used traditional methods, such as 
targeting locations similar to the ones where they had 
previously found Bigeye Tuna. 
The cost of fuel limited how far the fishermen could 
travel in search of Bigeye Tuna. Their fishing ground 
covered the area around 10-16°S and 108-120°E, the 
same region used in our data analysis. 
The fishermen did not target other species when 
fewer Bigeye Tuna were caught. They caught other 
species, such as small pelagic fishes ( Sardinella sp. or 
Euthynnus sp.), only for their own consumption during 
fishing trips (not as main targets). Therefore, we as- 
sumed that other catches did not influence the fishing 
effort. 
Political or management boundaries were not ma- 
jor problems facing this traditional fishing ground. 
Instead, the main constraints were the financial lim- 
its on long or distant fishing operations and the rapid 
fluctuations in fuel costs from week to week. The price 
of Bigeye Tuna depends on these factors: the location 
in which it is caught (fish caught farther from market 
are more expensive), the season (during the northwest 
monsoon, when fish abundance decreases, the price in- 
creases), and climate variability that affects environ- 
mental conditions (during El Nino event, fish generally 
are abundant and the price drops, and vice versa dur- 
ing La Nina event). 
Conclusions 
This study has shown the effects of ENSO-induced 
oceanographic conditions on catch rates of Bigeye Tuna 
in the EIO off Java. Spatiotemporal patterns in oceano- 
graphic conditions shown by the EOF, combined with 
the results of the GAMs, indicate that the 1997-98 El 
Nino event had a positive effect on catch rates of Big- 
eye Tuna in the EIO off Java. 
The EOF modes further highlight that interannual 
and seasonal time scales are the main factors that af- 
fect ocean current variability in the study area. The 
EOF analysis also provides evidence for the effects of 
the 1997-98 El Nino event in the EIO off the southern 
coast of Java — the dominant features being negative 
SSHA, cold SST, and high chlorophyll-a concentrations. 
In terms of these environmental variables, the binomi- 
al GAM confirmed that SST was the major factor that 
influenced Bigeye Tuna catches. These results indicate 
that the use of a GAM with 3 predictor variables may 
facilitate the identification of areas with potentially 
high Bigeye Tuna catch in the EIO off Java. 
Our results show significant effects of ENSO on Big- 
eye Tuna catches. For example, favorable oceanograph- 
ic conditions corresponded with the El Nino event, as 
indicated by the EOF and GAM analyses. We did not 
consider depth range data for Bigeye Tuna catches. 
Further investigations into prediction of fishing ground 
locations through the use of long-term, historical time 
series of environmental conditions and fishing ef- 
forts — fishery data sets of greater spatial and temporal 
resolutions than the data sets used in ours study — are 
needed to better understand the effects of climate vari- 
ability and fishing effort on changes in Bigeye Tuna 
catches in the EIO off Java. 
Acknowledgments 
The authors would like to thank the Directorate Gen- 
eral of Higher Education of the Republic of Indonesia 
and the Japan Science Society, under the Sasagawa 
Scientific Research Grant, for their support in funding 
this research. We thank the 3 anonymous reviewers for 
their valuable comments. We appreciate J. R. Bower for 
reading and improving this article. We thank the God- 
dard Space Flight Center/NASA and Physical Ocean- 
ography Distributed Active Archive Center for the 
production of chlorophyll-a and SST data, AVISO for 
the distribution of SSHA data, and the NOAA Climate 
Prediction Center for the use of its Nino 3.4 index. We 
also thank the incorporated company of Perikanan Nu- 
santara, Indonesia, which provided the fishery data. 
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