86 
Fishery Bulletin 95(1 ), 1997 
Locations of standard MARMAP stations (•) in the U.S. northeast shelf ecosystem and 
subarea boundaries (MAB=Middle Atlantic Bight; SNE=Southern New England; 
GBK=Georges Bank; and GOM=Gulf of Maine). 
Cape Hatteras (Sherman, 
1994). Plankton samples were 
collected within the ecosystem 
at monthly or bimonthly inter- 
vals from 1977 to 1987. Plank- 
ton surveys occupied approxi- 
mately 184 standard station lo- 
cations that were relatively un- 
changed during the 11-yr period 
(Fig. 1). Samples were also col- 
lected on trawl and dredge 
cruises at randomly selected lo- 
cations that varied yearly. Ar- 
eal coverage and station spac- 
ing on these surveys were simi- 
lar to broadscale plankton 
cruises. 
Zooplankton were collected at 
each station from one side of a 
61 -cm bongo frame fitted with 
a 0.333-mm mesh net. The gear 
was lowered at 50 m/min to 
within 5 m of the bottom, or to 
a depth of 200 m maximum, and 
retrieved at 20 m/min. Ship 
speed was adjusted to maintain 
a 45° angle to the towing wire. 
A digital flowmeter was posi- 
tioned in the center of the bongo 
frame to measure the volume of 
water filtered. All collections 
were preserved in 5% formalin. 
Samples were reduced to ap- 
proximately 500 organisms in 
the laboratory by subsampling 
with a modified box splitter. Zooplankton were sorted, 
identified, and counted at the Plankton Sorting Cen- 
ter, Szczecin, Poland. The total number of samples 
analyzed for this report was 10,715. The abundance 
of Centropages hamatus is expressed here as num- 
bers/100 m 3 of water filtered and includes only ad- 
vanced copepodite stages CV and CVI. Earlier 
copepodite stages were excluded because other cope- 
pods of similar size are undersampled by 0.333-mm 
mesh nets (Anderson and Warren, 1991). 
The seasonal abundance cycles of known preda- 
tors of copepods captured with the nets used during 
the surveys were examined to determine which might 
affect Centropages hamatus population levels. The 
three copepod predators examined in this study are: 
1) ctenophores, 2) the copepod Centropages typicus, 
and 3) chaetognaths. 
Sea-surface temperature was measured at each 
station to the nearest 0.1°C with a stem thermom- 
eter. During plankton surveys from 1977 to 1986, 
water bottles with reversing thermometers were used 
to collect water samples at standard depths in order 
to measure salinity and temperature. Measurements 
of bottom temperature were determined by means 
of the deepest bottle or by means of a special bottom- 
tripped water-bottle sampler in water less than 75 
m. Temperature and salinity data in 1987 were col- 
lected with a CTD (conductivity-temperature-depth) 
probe. Phytoplankton biomass was determined by 
measuring the concentration of chlorophyll a in the 
netplankton (>20 pmm) and the nanoplankton (<20 
pmm) size fractions from water samples down to 100 
m on plankton surveys from 1977 to 1984. These size 
fractions were summed to generate an estimate of 
total chlorophyll. The average water-column value 
of a variable for each station was calculated by ar- 
ithmetically integrating measurements over depth. 
More detailed accounts of sampling procedures and 
individual cruise tracks are given by Sibunka and 
Silverman (1984, 1989). 
