Abstract:
A generalized additive model (GAM) was constructed
to separate and quantify the effects of fishery-based
(operational) and oceanographic parameters on the
bigeye tuna (Thunnus obesus) catch rates at Palmyra
Atoll in the central Tropical Pacific. Bigeye catch, the
number of hooks per set, and set location from 4884
longline sets spanning January 1994 to December 2003
were used with a temporally corresponding El Nin˜o-
Southern Oscillation (ENSO) indicator built from sea
surface height (SSH) data. Observations of environmental
data combined with the results from the GAM
indicated that there is an increase in bigeye catch rates
corresponding to an increase in eastward advection
during the winter months of El Nin˜o events. A seasonal
pattern with higher bigeye catch rates from
December to April and a spatial pattern with higher
rates to the northeast and northwest of the atoll were
observed during this study period. It is hypothesized
that the combination of the eastward advection of the
warm pool coupled with vertical changes in temperature
during the winter months of El Nin˜o events increases
the availability of bigeye tuna in this region.
This increase in availability may be due to a change in
exploitable population size, location, or both.
