Distribution and Abundance of Larval 



American Lobsters, Homarus americanus Milne-Edwards, 



in the Western Inshore Region of 



Cape Cod Bay, Massachusetts 



ROBERT LAWTON,' ELIZABETH KOULOHERAS, 2 PHILLIPS BRADY,' 

 WENDELL SIDES, 3 and MANDO BORGATTI 1 



ABSTRACT 



Larval lobster {Homarus americanus) abundance and distribution in the western inshore region of Cape Cod 

 Bay, Mass., from 1974 to 1977 are reported. Lobster hatching generally began in mid-June, and the period of 

 larval occurrence ranged from 46 to 62 d over the time and area studied. Maximum densities of larvae were 

 collected in surface waters in July. Considerably more stage IV than stage I larvae were collected. Densities of 

 lobster larvae were similar to levels obtained in several other New England investigations with the notable ex- 

 ception of Buzzards Bay where hatching was substantially greater. 



INTRODUCTION 



The American lobster, Homarus americanus Milne- 

 Edwards, is the most valuable commercial resource harvested 

 in Massachusett's territorial waters. An intensive lobster fish- 

 ery occurs off Plymouth (Fig. 1) from March to November. 

 The lobster catch reported for Plymouth County amounted to 

 348 t and was valued at $1.1 million in 1974 (Beals and 

 Phelan J ). By 1980, landings increased to 918 t, valued at $4.0 

 million (Anderson et al. s ). 



Inshore lobstering in Plymouth is concentrated within a 5.6 

 km radius of Pilgrim Nuclear Power Station, located on the 

 western shore of Cape Cod Bay (Fig. 1). Because of the 

 economic value and proximity of this fishery to the power 

 plant and lack of information on site-specific larval ecology, 

 the Massachusetts Division of Marine Fisheries examined the 

 temporal and spatial distribution of lobster larvae from 

 1974 to 1977. This undertaking was part of an overall ecolog- 

 ical investigation to determine plant-related impact on marine 

 resources in Cape Cod Bay. 



Our objectives were to determine location of hatching areas, 

 density, and distribution of lobster larvae in the vicinity of 

 the power plant. Work conducted in 1974 was preliminary. We 

 expanded our inquiry in 1975 to investigate effects of wind on 

 larval distribution and to examine the occurrence and density 



of larvae in shallow water. In 1976, we increased sampling 

 frequency and concentrated efforts from Rocky Point north- 

 ward to Brant Rock (Fig. 1). Our intent in 1977 was to obtain 

 information on distribution of larvae at depth and further 

 definition of hatching and nursery areas. 



METHODS 



Study Area 



Cape Cod Bay, located at the southern extremity of the Gulf 

 of Maine, is a broad open water body bounded by the land- 

 form of the eastward and northward extension of Cape Cod. 

 The substrate in the overall study area, which included sta- 

 tions from Brant Rock to Scorton Ledge (Fig. 1), is primarily 

 smooth sand interrupted by submerged ledges. This habitat 

 may support high lobster densities (Cobb 1971). 



Hatching, distribution, and density of larvae are influenced 

 by an interaction of water temperature, salinity, and current 

 patterns. Annual surface and bottom water temperatures 

 generally range from - 1 °C in February to 23 °C in August and 

 from - 1 °C in February to 21 °C in September, respectively 

 (Lawton et al. 6 ). The water column is stratified from June to 

 November with a thermocline evident between 5 and 10 m 

 (Doret et al. 7 )- Surface salinities, ranging primarily from 

 28 to 35°/oo, are influenced by both the ocean and, to a lesser 

 degree, drainage from watersheds. The overall water move- 



1 Massachusetts Department of Fisheries, Wildlife, and Recreational Vehicles. 

 Division of Marine Fisheries, 100 Cambridge St., Boston, MA 02202. 



'Massachusetts Department of Fisheries, Wildlife, and Recreational Vehicles, 

 Division of Marine Fisheries, 100 Cambridge St., Boston, Mass.; present address: 

 Department of Quality Engineering, Lakeville Hospital, Lakeville, MA 02346. 



'Massachusetts Department of Fisheries, Wildlife, and Recreational Vehicles, 

 Division of Marine Fisheries, 100 Cambridge St., Boston, Mass.; present 

 address: 1 14 Gilson St., Scituate, MA 02066. 



'Beals, R. W., and J. J. Phelan. 1976. Massachusetts coastal lobster fishery 

 statistics. Mass. Div. Mar. Fish. Tech. Rep. 10, 19 p. 



'Anderson, C. 0., Jr., C. B. Kellogg, and G. Nash. 1980. 1980 Massachusetts 

 lobster fishery statistics. Mass. Div. Mar. Fish. Tech. Ser. 15, 20 p. 



•Lawton, R. P., W. T. Sides, E. A. Kouloheras, R. B. Fairbanks, M. 

 Borgatti, and W. S. Collings. 1978. Final report on the assessment of possible 

 effects of Pilgrim Nuclear Power Station on the marine environment. Project 

 Report No. 24 (1970-1977). Massachusetts Division of Marine Fisheries. In: 

 Marine ecology studies related to operation of Pilgrim Station. Final Report, 

 July 1969-December 1977. Vol. 1, sect. III. 9, 19 p. Nuclear Engineering 

 Department, Boston Edison Company, 800 Boylston St., Boston, MA 02199. 



'Doret, S. C, D. R. F. Harleman, A. T. Ippen, and B. R. Pearce. 1973. 

 Characteristics of condenser water discharge on the sea surface. R. M. Parsons 

 Laboratory for Water Resources and Hydrodynamics. Department of Civil 

 Engineering, Massachusetts Institute of Technology, Boston, Mass., 156 p. 



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