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(10%), and the remainder (10%) taken by troll gear and a variety of artisanal gears, mostly in
eastern Indonesia and the Philippines. The WCPCA tuna catch (2,426,195 t) for 2008 represented
81% of the total Pacific Ocean catch of 3,009,477 t, and 56% of the global tuna catch (the
provisional global estimate for 2008 is just over 4.3 million t).
57. The skipjack stock assessment undertaken in 2008 indicates that the skipjack stock is not in
an overfished state, nor is overfishing occurring. The yellowfin tuna stock assessment undertaken
in 2009 indicates that overall, the stock is not in an overfished state, nor is overfishing occurring;
however, there is heavy exploitation in the western equatorial Pacific where 95% of the fishery
occurs, and the current status is due to the buffering that occurs as a result of low levels of
exploitation in adjacent subtropical areas. The streamlined bigeye stock assessment undertaken in
2009 indicates that the stock is nearing an overfished state and that overfishing is occurring. The
South Pacific albacore assessment undertaken in 2009 indicates that the stock is not in an
overfished state, nor is overfishing occurring, however there is a moderate level of depletion of
the portion of the stock targeted by the longline fisheries active within the exclusive economic
zones (EEZs) of several countries.
58. In response to questions, Dr Hampton provided the following additional information:
a. Although fishing mortality for bigeye is much greater than the fishing mortality at
maximum sustainable yield (MSY), stock biomass has not declined as might have
been expected because recruitment during the last decade has been higher than
average. If recruitment were to fall, the stock biomass would decline to levels below
current levels (estimated to be 20% of unfished biomass). Biomass trajectories of
tuna populations at such low stock sizes are not well known but such a situation
could lead to rapid and cascading further declines.
b. No specific assumptions are made in the models for unreported catches, although the
models do take into account illegal or unregulated catches.
c. Sets on unassociated yellowfin tuna usually catch larger-sized individuals.Thus, if a
fish aggregation device (FAD) closure leads to more sets on un-associated schools,
yellowfin catches would be expected to increase.
d. In the forthcoming (2010) stock assessment for skipjack, SPC will work with
Japanese scientists to expand the model area and incorporate information on regional
migration patterns.
e. It is not clear whether inward migration from other areas of the western and central
Pacific Ocean (WCPO) compensate for the estimated stock declines in the western
portion of the WCPO (Region 3), but new tagging information should indicate
whether such a buffering effect may occur.
f. The significantly increasing number of yellowfin catches in recent years is due to a
large reported increase in medium to large un-associated purse-seine sets. The
increased number of skipjack catches are part of a pattern of increasing catches in
the early 1980s and since 2000; these will be further investigated.
g. The WCPFC and IATTC stock assessments assume that there are separate stocks of
bigeye in the WCPO and eastern Pacific Ocean (EPO). This assumption has been
tested in several ways over the years and the results support the conclusion that stock
assessment results based on this assumption are not dissimilar to those based on a
single-stock hypothesis.
h. The stock assessments make good use of a long and detailed historical dataset on
yellowfin length and weight extending back to 1950.
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