Distribution, Relative Abundance, and Seasonal 



Production of American Lobster, Homarus americanus. 



Larvae in Block Island Sound in 1978 



MICHAEL J. FOGARTY, 1 MARTIN A. HYMAN, 2 GEORGE F. JOHNSON, 3 



and CLEMENT A. GRISCOM 4 



ABSTRACT 



Neuslon samples were collected at eight station sites in Block Island Sound at approximately weekly 

 intervals from 3 May through 1 September 1978, and sorted for lobster {Homarus americanus) larvae. Larvae 

 were collected between 1 June and 22 August. Fourth stage larvae were numerically dominant, comprising 63% 

 of the 1,030 larvae collected in this survey. Total production of stage 1 larvae in Rhode Island Statistical Area 4 

 estimated from survey data was 2.514 X 10" larvae. A minimum estimate of potential stage I production in Area 

 4 based on population size determined by cohort analysis and relative population fecundity indicated that at least 

 3.232 X 10 7 larvae could have been produced. Stepwise multiple regression analysis of hydrographic and 

 climatologieal variables on total larval density demonstrated that water temperature and wind velocity 

 explained 61.5% of the observed variance. 



INTRODUCTION 



The American lobster, Homarus americanus, is among the 

 most valuable commercially exploited species in Rhode Island. 

 Preliminary commercial landings in 1980 were 1,100 t with an 

 estimated value of $5.6 million. Due to the importance of this 

 species to the economy of Rhode Island, investigations into 

 several aspects of lobster population dynamics were initiated in 

 1974. These studies provided information on growth and 

 mortality (Russell et al. s ), local movements and migratory 

 behavior (Fogarty et al. 1980), gear selectivity (Fogarty and 

 Borden 1980), trawl induced injury and mortality (Ganz 6 ), and 

 commercial catch statistics (Simon'). 



Despite the recent attention devoted to the behavior, ecolo- 

 gy, and population biology of juvenile and adult American lob- 

 ster, relatively little is known of the pelagic larval stages. The 

 present study was designed to investigate the seasonal and 

 spatial distribution of lobster larvae in Block Island Sound. 

 We derived a preliminary estimate of larval production in the 



survey area using stage 1 density adjusted for development 

 time and mortality. For companion, potential egg production 

 was calculated using information on population structure, sex 

 ratios, size at maturity (Russell et at. footnote 5), and relative 

 population fecundity (Saila et al. 1969). 



MATERIALS AND METHODS 



Neuston samples were collected at approximately weekly in- 

 tervals from 3 May through 1 September 1978 at eight stations 

 in Block Island Sound (Fig. 1) and sorted for lobster larvae. 

 Replicate samples were collected with paired neuston nets (1 

 m x 2 m opening; 0.946 mm mesh) deployed from two side 

 booms aboard a 20 m research vessel. When sampling, the nets 

 were positioned forward of the stern wake and outside of the 

 bow wake to ensure an undisturbed sample. The position of 

 the nets was adjusted to sample the upper 0.5 m of the water 

 column. Standard tows were of 20 min duration at approxi- 

 mately 3.7 km/h. During periods of high ctenophore abun- 

 dance, when the filtration efficiency of the nets was reduced, 



'Rhode Island Department of Environmental Management, 150 Fowler Street, 

 Wickford, R.I.; present address: Northeast Fisheries Center Woods Hole Laboratory, 

 National Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 



^Graduate School of Oceanography, Division of Marine Resources, University of 

 Rhode Island, Narragansett, R.I.; present address: Graduate School of Oceano- 

 graphy, Cetacean Turtle Assessment Program, University of Rhode Island, 

 Narragansett, RI 02882. 



'Graduate School of Oceanography, University of Rhode Island, Narragansett, 

 R.I.; present address: Martin Marietta Corp., 1450 South Rolling Road, Baltimore, 

 MD 21227. 



'Graduate School of Oceanography, Division of Marine Resources, University of 

 Rhode Island, Narragansett, RI 02882. 



'Russell, H. J., D. V. D. Borden, and M. J. Fogarty. 1978. Management 

 studies of inshore lobster resources. Final report. State-Federal Lobster Manage- 

 ment Program Contract No. 03-4-043-360, 78 p. 



'Ganz, A. R. 1979. Evaluation of otter trawl induced lobster damage. Final 

 report. Commercial Fisheries Research and Development Act Contract No. 

 04-7-043-44041 , 23 p. 



'Simon, B. M. 1980. Lobster logbook and statistical analysis. Segment report. 

 Commercial Fisheries Research and Development Act Contract 04-78-D01-R1B-B. 



WEEKAR4UG 



PtHNj JUDITH . 



M. BLOCK : 

 Cl> ISLAND :' 



Figure 1. 



-Location of sample sites in Block Island Sound. 1978. Shaded area 

 indicates Rhode Island Statistical Area 4. 



23 



