The Spatio-Temporal Distribution of 



American Lobster, Homarus americanus, 



Larvae in the Cape Cod Canal and Approaches 



W. STEPHEN COLLINGS, 1 CHRISTINE COOPER-SHEEHAN, 2 

 SALLY C. HUGHES, : and JAMES L. BUCKLEY 1 



ABSTRACT 



The spatial and temporal distribution of larval lobsters in northern Buzzards Bay, the Cape Cod Canal, and 

 southwestern Cape Cod Bay was examined during 1976-78. Hatching generally began in late May when bottom 

 water temperatures approximated 10°C. Most larvae had settled out of the water column by mid-August, but 

 larvae were occasionally collected as late as October. Larvae were concentrated at nearshore stations by on- 

 shore winds in Buzzards Ba\ and Cape Cod Bay. A higher percentage (71%) of the total larvae were collected 

 when cloud cover was 25° 7 o or less. Larvae were collected in water ranging in temperature from 10.3° to 25.5 °C. 

 Salinities ranged from 23.3 to 35.5°/oo. Percent stage composition was comparable with that found in southern 

 Buzzards Bay. The density of lobster larvae in the Cape Cod Canal was similar at all depths, but larvae were 

 associated with the surface water la>er in Buzzards Ba> and Cape Cod Bay. In 1976, 1977, and 1978, an estimated 

 13.5, 26.0, and 9.2 million lanae, respectively, were deposited from the Cape Cod Canal into Cape Cod Bay. 



INTRODUCTION 



Preliminary larval lobster distribution studies carried out in 

 Cape Cod Bay by the Massachusetts Division of Marine Fish- 

 eries prior to 1974, and intensive efforts by both the Division 

 and a private contractor (Marine Research, Inc.) from 1974 to 

 1977, revealed few larvae in Cape Cod Bay. A large commer- 

 cial fishery exists in Cape Cod Bay and concentrations of egg- 

 bearing female lobsters are occasionally observed in the Cape 

 Cod Canal and Buzzards Bay; accordingly the possible impor- 

 tance of larval transport to Cape Cod Bay and the effects of an 

 additional fossil-fueled electrical generating station on the 

 Cape Cod Canal were investigated. A 3-yr study of the spatial 

 and temporal distribution of larval lobsters in northern Buz- 

 zards Bay, the Cape Cod Canal, and southwestern Cape Cod 

 Bay was initiated in the spring of 1976. 



STUDY AREA 



Buzzards Bay is a marine embayment approximately 46 km 

 long by 19 km wide (Fig. 1) with a maximum depth of 41 m 

 and an average depth of 1 1 m (Anraku 1964; Gilbert et al. 3 ). 

 In upper Buzzards Bay, the salinity varies from 26.0 to 

 35. 5°/ oo with surface water temperatures ranging from - 1 ° 

 to 28.0°C and bottom temperatures from -1° to 25 °C 

 (Collingsetal. 4 ). 



Commonwealth Energy, Canal Electric Company, Cranberry Highway, 

 Wareham, MA 02571. 



^Massachusetts Division of Marine Fisheries, 100 Cambridge Street, Boston, 

 MA 02202. 



'Gilbert, T., A. Clay, and A. Barker. 1973. Site selection and study of ecologi- 

 cal effects of disposal of dredged materials in Buzzards Bay, Massachusetts. 

 Prepared for Department of the Army, New England Division, Corps of En- 

 gineers by New England Aquarium under Purchase Order No. DACW 33, 

 73-C-0024, 70 p. 



'Collings, W. S., C. C. Sheehan, S. C. Hughes, and J. L. Buckley. 1981. The 



Cape Cod Bay is a nearly circular embayment of the Atlan- 

 tic Ocean with water depths reaching 91.5 m but with an aver- 

 age depth of 25 m (Parsons 1918; Anraku 1964). Surface sa- 

 linities range between 29.0 and 36.0°/oo, and while surface 

 water temperatures can exceed 20°C in the summer, bottom 

 temperatures rarely exceed 15°C. Currents in both bays are 

 weak, seldom exceeding 1.1 km/h (Collings et al. footnote 4). 



The Cape Cod Canal is a sea level passage connecting Cape 

 Cod Bay with Buzzards Bay. With a mean tidal range in Cape 

 Cod Bay of 2.8 m and of 1 .2 m in Buzzards Bay, the difference 

 in phase and amplitude of the tides produce changes in the 

 slope of the water in the Canal. Consequently, there is a 

 regular reversal in current at approximately 6 h intervals. Cur- 

 rents have an average speed of 6.5 km/h in midchannel, but 

 during spring tides increase to about 7.4 km/h (Anraku 1964). 

 Surface salinity varies from 28.0 to 34.0%o (Collings et al. 

 footnote 4), and water temperatures range from -l°to25°C. 

 The lack of thermal stratification in the Canal is due to the 

 strong currents and turbulence (Fairbanks et al. 5 )- 



METHODS AND MATERIALS 



Neuston samples were collected at 7 stations during 1976, 16 

 in 1977, and 10 in 1978 (Fig. 2). Stations were sampled on a 

 weekly basis from the first week in May until lobster larvae 

 were no longer obtained in neuston samples. Factors that pre- 

 vented sampling were rough seas and high concentrations of 

 ctenophores (Mnemiopsis leidyi) or crab larvae. 



effects of power generation on some of the living marine resources of the Cape 

 Cod Canal and approaches. Massachusetts Department of Fisheries, Wildlife, 

 and Recreational Vehicles, Div. Mar. Fish., 100 Cambridge Street, Boston, 

 Mass., 212 p. + appendices. 



'Fairbanks, R. B., W. S. Collings, and W. T. Sides. 1971. An assessment of the 

 effects of electrical power generation on marine resources in the Cape Cod Canal. 

 Mass. Dep. Nat. Resour., Div. Mar. Fish., 48 p. + appendix. 



35 



