85 
Abstract .—The annual cycle of 
abundance and the monthly distribu- 
tions of the copepod Centropages 
hamatus are described for U.S. north- 
east continental shelf waters from 
plankton samples collected approxi- 
mately bimonthly from 1977 to 1987. 
The copepod was found distributed 
throughout the study area with a 
strong onshore-offshore abundance 
gradient. After its annual low, C. 
hamatus was found to increase in abun- 
dance slowly along the coast and to ex- 
pand offshore following the northward 
progression of spring conditions. The 
highest monthly mean abundance es- 
timates of C. hamatus were found on 
Georges Bank during the month of July. 
Distribution begins to constrict inshore 
following peak abundance periods. 
Examination of environmental vari- 
ables revealed that in general Centro- 
pages hamatus was prevalent when 
surface temperatures ranged from 12 
to 17°C, when water-column chloro- 
phyll levels were high, and where sa- 
linity was low on the shelf. The popu- 
lation in the Middle Atlantic Bight sub- 
area declines sharply as water tem- 
peratures rise in summer and does not 
begin to recover until temperatures 
decline in the fall. In contrast, popula- 
tions in the more northern regions de- 
crease slowly from peak abundance and 
do not increase from their annual low 
until water temperatures rise in early 
spring. The pelagic population that sur- 
vives through low abundance periods 
is concentrated in shoal or inshore (or 
both) waters where temperature is low 
and phytoplankton biomass high. There 
was no evidence from survey data that 
predation by ctenophores, chaetognaths, 
or the copepod Centropages typicus has 
a major effect on C. hamatus abundance. 
Manuscript accepted 10 July 1996. 
Fishery Bulletin 95:85-98 ( 1997). 
Persistent spatial and temporal 
abundance patterns for late-stage 
copepodites of Centropages hamatus 
(Copepoda: Calanoida) in the U.S. 
northeast continental shelf ecosystem 
Joseph Kane 
National Marine Fisheries Service, NOAA 
28 Tarzwell Drive, Narragansett, Rhode Island 02882-1 199 
E-mail address: jkane@whsun 1 .wh.whoi.edu 
The calanoid copepod Centropages 
hamatus (Lilljeborg, 1853) is one of 
the dominant members of the zoop- 
lankton assemblage found within 
North Atlantic shelf waters (Davis, 
1987; Sherman et al., 1987 ). The 
species has a wide latitudinal range 
that is reported to be as far north 
as Labrador (Pinhey, 1926) and 
southward to coastal waters off 
Florida in the Gulf of Mexico (Marcus, 
1989). It occurs primarily in shel- 
tered, coastal, and shoal regions of 
the continental shelf. This omni- 
vorous copepod produces subitan- 
eous eggs during the breeding sea- 
son and also can produce diapausal 
ones in response to an environmen- 
tal trigger (Pertzova, 1974; Marcus, 
1989). McLaren (1978) estimated 
that generation period is compara- 
tively short, 21-25 days at 12-13°C, 
and describes C. hamatus as a 
highly productive and ecologically 
efficient component of the zooplank- 
ton community. Sherman et al. 
(1987) reported that it is a major 
prey item of larval, juvenile, and 
adult fish stocks within continental 
shelf waters. 
The National Marine Fisheries 
Service has monitored the zooplank- 
ton populations of the U.S. north- 
east shelf ecosystem with broad- 
scale surveys since 1977 as part of 
the MARMAP (Marine Resources 
Monitoring, Assessment, and Pre- 
diction) program (Sherman, 1980). 
The resulting historical data set 
provides the information needed to 
form a baseline for detection of fu- 
ture changes to the ecosystem. Pre- 
vious reports on the annual abun- 
dance cycle of Centropages hamatus 
within the ecosystem have been lim- 
ited to specific areas or to compara- 
tively short periods (or both) (Bige- 
low, 1926; Deevey, 1956, 1960; 
Judkins et al., 1980; Davis, 1987; 
Sherman et al., 1987; Grant, 1988; 
Kane, 1993). No description of the 
monthly distribution of the copepod 
in this region has been published 
from collected data. This report uses 
information collected during 
MARMAP surveys from 1977 to 
1987 to describe the persistent dis- 
tribution and abundance patterns 
of C. hamatus throughout the eco- 
system. Measurements of salinity, 
temperature, bottom depth, chloro- 
phyll, and potential predator abun- 
dance were considered to gain in- 
sight into factors affecting the dis- 
tribution and annual abundance 
cycle of C. hamatus. 
Methods 
Sample collection and analysis 
The U.S. northeast shelf ecosystem 
extends from the Gulf of Maine to 
