80 
Fishery Bulletin 111(1) 
A 
B 
Figure 1 
Map of study area in our examination of the distribution of ommastrephid 
paralarvae in the eastern tropical Pacific with (A) oceanography (after 
Fiedler and Talley, 2006) and (B) sampling stations from cetacean and eco- 
system assessment surveys conducted by the Southwest Fisheries Sci- 
ence Center (NOAA) from 1998 to 2006. Two plankton tows, one each with 
a manta and a bongo net, were conducted each evening approximately 2 h 
after sunset. STSW=Subtropical Surface Water. TSW=Tropical Surface Water. 
ESW=Equatorial Surface Water. 
the Equatorial Countercurrent, nominally along 10°N 
latitude (although the exact location varies season- 
ally) and 2) the Costa Rica Dome, an area of thermo- 
cline doming, nominally at 9°N latitude, 90°W longi- 
tude, although this feature too varies in location and 
degree of development through time, seasonally and 
interannually. 
The study area for this research 
forms a polygon that circumscribes the 
oceanic waters from the U.S. -Mexico 
border west to Hawaii, and south to 
central Peru. Cetacean and ecosystem 
assessment cruises were conducted in 
this region by the Southwest Fisheries 
Science Center (NOAA Fisheries) from 
late July to early December of 1998, 
1999, 2000, 2003, and 2006 (Fig. IB), 
with the University-National Oceano- 
graphic Laboratory System (UNOLS) 
research vessel Endeavor (1998), and 
the NOAA Ships David Starr Jordan 
(all years), McArthur (1998, 1999, 
2000), and McArthur II (2003, 2006). 
Plankton were sampled with 2 types 
of net tows, conducted ~2 h after sun- 
set each day, for a total of 979 manta 
(surface) tows and 762 bongo (oblique) 
tows over the 8-year period. On the 
McArthur II in 2006, during one leg of 
the cruise, medium-size jigs and rods 
were used to fish for adult squid from 
1 to 2 h after sunset. 
Manta nets (Brown and Cheng, 
1981) with 0.505-mm mesh were towed 
for 15 min at a ship speed of 1. 0-2.0 
kn, with all deck lights off. Bongo nets 
(McGowan and Brown 2 ; Smith and 
Richardson, 1977), consisting of a pair 
of circular net frames with 0.505-mm 
or 0.333-mm mesh, were towed for a 
15-min double oblique haul to a depth 
of -200 m at a ship speed of 1. 5-2.0 
kn. The net was lowered continuously 
at about 35 m/min, held at -200 m for 
30 s, and then was retrieved at about 
14 m/min, with the angle of stray al- 
ways maintained at -45°. 
Volume of water filtered during 
manta and bongo tows was estimated 
with a flowmeter suspended across the 
center of the net. Contents of the co- 
dends were preserved in 5% formalin 
buffered with sodium borate. In 2003 
and 2006, the contents of one codend 
of each bongo tow were frozen in sea- 
water at -20° C, and the contents of 
the other were preserved in 5% forma- 
lin. Also in 2006, the contents of one 
codend of every fourth bongo tow (38 
samples total) were preserved in 70% 
ethanol instead of formalin. 
2 McGowan, J. A., and D. M. Brown. 1966. A new opening- 
closed paired zooplankton net. Univ. Calif. Scripps Inst. 
Oceanogr. Ref. 66-23, 56 p. Scripps. Inst. Oceanogr., Univ. 
Calif, San Diego, CA. 
