A Snapshot of the Tropical Tuna Purse Seine Large-Scale Fishing ...

Figure 4. Relationship between between FHV (m 3 ) and LOA (m).
3.2.4 FHV vs GRT
The relationship between FHV (m 3 ) and GRT (tonnes) followed a linear relationship
(Figure 5):
FHV = 524.44+0.6733*GRT (n=324, R 2 =0.60)
For the smaller vessels, some of the data seem to follow a relationship through the
origin (which is logical) while others do not. There is not enough data available to
identify erroneous records.
Figure 5. Relationship between between FHV (m 3 ) and GRT (t).
3.3 Filling in missing values
Taking into consideration the goodness of fit of the various relationships in Section 3.2,
the following approach was taken to fill missing values in the database, aiming to
estimate FHV for all vessels that did not have this information:
1. Fill in LOA: If GRT is available, then use the GRT-LOA relationship in Section 3.2.1
(this was done for 281 vessels). Otherwise, set LOA to average LOA for other
vessels of the same Flag (this was done for 6 vessels).
2. Fill in FHV: If FCC available, use the FHV-FCC relationship from Section 3.2.2 (this
was done for 276 vessels). Otherwise, use FHV-LOA relationship from Section
3.2.3 (this was done for 839 vessels).
3.4 The global tuna purse seine fleet
We estimated that 1,664 purse seine vessels were authorized to fish for tunas at the end
of 2011. Using largely extrapolated data, we estimate that these vessels have a combined
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