Seasonal and Areal Distribution of Zooplankton 



in Coastal Waters of the Gulf of Maine, 



1965 and 1966 



By 



KENNETH SHERMAN, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 West Boothbay Harbor, Maine 04575 



ABSTRACT 



A description is given of the abundance, composition, and seasonal variations 

 in distribution of zooplankton. Eleven nnajor taxa were represented in the samples. 

 Six were holoplanktonic, and five were meroplanktonic. Copepods were the dominant 

 zooplankters during all seasons in both years. Zooplankton volumes in both years 

 followed similar areal trends. Mean annual volumes were highest in the western area 

 (Cape Ann to Cape Elizabeth), moderate in the central area (Cape Elizabeth to Mt. 

 Desert Island), and low in the eastern sector (Mt. Desert Island to Machias Bay). 

 Zooplankton volumes were generally lower in 1966 than in 1965. Areal and annual 

 variations in the abundance of zooplankters are discussed in relation to hydrography. 



INTRODUCTION 



The Bureau of Commercial Fisheries in 

 1963 began an investigation of the effects of 

 the environment on the availability and abun- 

 dance of herring, Clupea harengus harengus L,., 

 in coastal waters of the Gulf of Maine. Studies 

 of zooplankton were undertaken as part of this 

 investigation. Sampling was designed tonneas- 

 ure variations in composition, distribution, 

 and abundance of the larger zooplankters, 

 particularly calanoid copepods, an innportant 

 food of herring. This is the third in a series 

 of reports (see Sherman, 1965 and 1966) 

 on the coastal zooplankton assemblage in 

 the Gulf of Maine. 



METHODS 



Sannpling in 1965 and 1966 was similar to 

 that in the earlier surveys of 1963 and 1964. 

 Four stations in each of three Gulf of Maine 

 coastal areas--western (Cape Ann to Cape 

 Elizabeth), central (Cape Elizabeth to Mt. 

 Desert), and eastern (Mt. Desert to Machias 

 Bay)--were sannpled seasonally on cruises of 

 the research vessel Rorqual (fig. 1). Samples 

 were collected with a Gulf III sampler fitted 

 with a 20.4-cm. nose cone and metal netting 

 (aperture width, 0.37 mm.). Step-oblique tows 

 of 30 minutes-- 10 minutes each at 20 m., 

 10 m., and the surface- -were made during 

 daylight. The amount of water strained was 



determined from a calibrated flow meter 

 mounted on the tail section of the sampler. 

 Each tow covered about 5.6 km. (3 nautical 

 miles) and filtered about 200 m.3 of water. 

 The towing speed was 308 cm. /sec. (6 

 knots). 



Volumes of the samples of zooplankton were 

 nneasured in the laboratory by the nnercury- 

 immersion method (Yentsch and Hebard, 1957). 

 Ctenophores, large coelenterate remains 

 (>2 cnn. long), and all fish larvae were ex- 

 cluded. Zooplankton samples were divided 

 into aliquots ranging from a half to a sixty- 

 fourth, depending on the mass of the sannple, 

 and sorted into major taxonomic groups. 

 Copepods were identified to species, and 

 numbers of copepods and other zooplankters 

 per 100 m,^ of water were calculated. 



ABUNDANCE, COMPOSITION, AND 

 DISTRIBUTION OF ZOOPLANKTON 



Zooplankton Volumes 



Seasonal trends in zooplankton volumes in 

 1965 and 1966 were similar in the western 

 area of the Gulf (Fig. 2). Volumes increased 

 fronn a winter low to a summer high and 

 decreased in the fall. In the eastern area 

 volumes were low (<2.5 cc./lOO m.^ ) in all 

 seasons during both years. Seasonal varia- 

 tions were greatest in the central area. In 

 1965 volumes were high in the winter, but 



