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Fishery Bulletin 11 6(1) 
30°N 
25 
20 
15 
Figure 6 
Maps of the spatial distribution of total estimated inciden¬ 
tal catch per unit of effort in the eastern Pacific Ocean off 
Mexico, the number of fish per set indicated by the size 
of the white circles, and mean values of (A) sea-surface 
temperature (measured in degrees Celsius), (B) chloro- 
phyll-a concentration (measured in milligrams per cubic 
meter) and (C) sea-surface height (measured in meters) 
for the 10-year period 2004-2013. The scale at the top of 
each panel indicates levels for 1 of the 3 environmental 
parameters. 
~2-4 months after the conclusion of the upwelling sea¬ 
son along the west coast of BCP, when the food web is 
fully “mature” for large pelagic pray, and SST is opti¬ 
mal for dolphinfish. 
In the ocean zone where a high ICPUE is reported, 
there is also a current pattern that seasonally opti¬ 
mizes the SST for dolphinfish. The California Current 
System is the eastern part of the North Pacific Sub¬ 
tropical Gyre, which reaches the BCP (Badan, 1997). 
Part of the California Current turns westward, at 
around 15°N, 112°W, as evident by the curvature of 
the isotherms, and becomes the North Equatorial Cur¬ 
rent (Karl, 1999; Fiedler and Talley, 2006). In this area 
thermal fronts occur when the cold California Current 
meets the Eastern Pacific Warm Pool, an area in the 
central Pacific Ocean off the coast of Mexico, character¬ 
ized by temperatures > 27.5°C all year long (Fiedler 
and Talley, 2006; Kessler, 2006), as a result of large 
net heat flux and poor wind mixing (Wang and Enfield, 
2001, cited by Fiedler and Talley, 2006). Additionally, 
the North Pacific Subtropical Gyre is anticyclonic and 
characterized by low productivity and a high pressure 
center (Lalli and Parsons, 1997), both of which suggest 
that low production areas occur on both sides of the 
branch of the California Current that joins the Equa¬ 
torial Current System; a branch that spatially agrees 
with the oceanic area of high ICPUE. 
The direction and intensity of the California Cur¬ 
rent has a pattern similar to that of oceanic wind 
(Pantoja et al., 2012), and both are strongest during 
winter (Martinez-Rincon et al., 2009; Marin-Enriquez, 
2012). Assuming that the 3-month lag hypothesis of 
Ortega-Garcla and Lluch-Cota (1996) also applies to 
this oceanic area, because dolphinfish arrive during 
May-June, ~3-4 months after the winter season, the 
California Current enters a dormant state, and tropi¬ 
cal water masses, with high temperature and low sa¬ 
linity (Torres-Orozco, 1993) move northwards, bringing 
the preferred SST values to the high ICPUE zone for 
dolphinfish. 
Survey quadrants with high ICPUE were scattered 
throughout the southernmost part of the study area, 
especially from February through April (Suppl. Fig. 1) 
(online only). This zone (0°-10°N) is under the influence 
of the Equatorial Current System and is a highly pro¬ 
ductive zone because of the upwelling caused by the 
trade winds (Martmez-Rincon et al., 2009). In the zone 
of the equatorial cold-upwelled water tongue, trade 
winds, and upwelling are more intense during winter 
months (Kessler, 2006, fig. 9). Mann and Lazier (1996) 
suggested that high trophic level predators, such as 
sharks, tunas, and other fish use this area as feeding 
grounds because of the high prey abundance resulting 
from the nutrient-rich upwelling process. Bocanegra 
Castillo (2007) suggested that billfish, sharks, and dol¬ 
phinfish feed on a wide variety of prey in this area, 
such as crustaceans, small fish, and squid. The rela¬ 
tively high ICPUE in this zone could then be explained 
by the time lag that it takes the trophic web to “climb” 
up to the trophic levels of the prey that dolphinfish 
