Distribution and Abundance of Lobster Larvae 

 (Homarus americanus) in Block Island Sound 



BRENDAGOLBERGBIBB, 1 RONALD L. HERSEY, 2 and ROCCO A. MARCELLO, JR. 3 



ABSTRACT 



The distribution and abundance of lobster larvae along a transect in Block Island Sound was studied in 

 1977 and 1978. We examined the seasonal, diel, and vertical distribution of lobster larvae. The study was ex- 

 panded to four transects in 1979 to examine broader spatial patterns. 



Lobster larvae were seasonally abundant, appearing in late May or early June and disappearing by late 

 August. Larvae were generall> more abundant at the surface than in near-bottom waters, but occasional high 

 concentrations of larvae were observed near the bottom. Surface abundance tended to be higher in daylight 

 than at night. Stage IV larvae were more abundant in 1978 than anticipated from abundance of stage I larvae, 

 possibly suggesting recruitment from adjacent areas. In the 1979 study, stage I larvae were most abundant in the 

 eastern section of the survey area. 



INTRODUCTION 



This paper describes an intensive study of the distribution 

 and relative abundance of lobster larvae (Homarus americanus 

 Milne-Edwards) in Block Island Sound during 1977-79. The 

 objectives of the study were to provide information on diel 

 variation, depth distribution, spatial differences, seasonal 

 variation, and yearly variation of lobster larvae in Block Island 

 Sound to examine potential impacts of a proposed nuclear 

 power facility at Charlestown, R.I. 



METHODS 



The 1977 and 1978 surveys consisted of weekly sampling 

 using a Tucker net at four stations along a transect off East 

 Beach, Charlestown, R.I. (Fig. 1). Surface samples were taken 

 day and night at four stations. Bottom samples were taken 

 at two stations only, EB-B and EB-C. In 1977, stations EB-B, 

 EB-C, EB-D, and EB-E were sampled. In 1978, stations EB-A, 

 EB-B, EB-C, and EB-D were sampled. In 1979, the sampling 

 area was expanded to 12 stations along four transects: off 

 Weekapaug (WK), East Beach (EB), Nebraska Shoals (NS), 

 and Point Judith (PJ). Surface samples were collected in day- 

 light every 3 to 4 d using a neuston net along these transects. 



In 1977 and 1978, preliminary sampling was carried out at 

 stations EB-B and EB-C to determine when larvae first 

 appeared. During the subsequent weeks, sampling was carried 

 out at all stations and depths described above until no more 

 larvae were observed. The period of sampling extended from 

 May through August 1977 and 1978, and May through mid- 

 June in 1979. Plankton sampling along the same transect was 

 carried out through fall, winter, and spring of 1977 and 1978 

 and early 1979. 



All 1977 and 1978 samples were collected using an opening 

 and closing Tucker net (Hopkins et al. 1973), equipped with a 

 2 m x 2 m, 0.950 mm mesh, 8 m long net. The mouth of the 

 net sampled at a 45 ° angle with a resultant 2 m x 2 m effective 

 sampling area. Surface tows were taken with the upper bar of 

 the Tucker net about 10 cm out of the water. Bottom tows 

 were made with the center of the Tucker net about 3 m off the 

 bottom. The net was towed between 0.77 and 1.29 m/s for 

 approximately 12 min. Estimated sample volumes were gener- 

 ally between 2,000 and 4,000 m'. Triplicaie lows were made 

 either in a westerly or easterly direction. 



Samples in 1979 were taken with a neuston net having 1 m x 

 2 m mouth, length of 4 m, and 1 mm mesh. Simultaneous 

 paired tows were made with approximately 10 cm of net out of 

 the water. Sample volumes were generally 1,500 to 2,000 m 3 . 

 A paired-comparison of sampling efficiency using the Tucker 

 and neuston nets was performed in 1979 (Bibb et al. 1983). 



Samples were reduced in volume to 2 1 and preserved in 10% 

 buffered formaldehyde for analysis. 



Temperature and salinity measurements were taken during 

 plankton surveys at the surface and bottom at each station in 

 1977 and 1978 and at the surface in 1979 using a calibrated 

 Beckman Model RS-5 salinometer*. The temperature output 

 was calibrated using a NBS-traceable thermometer and the 

 salinity output using standard seawater, and an appropriate 

 correction factor derived. Continuous temperature data was 

 recorded using Aanderaa thermistors deployed at stations 

 EB-A and EB-B (Snooks and Jacobson s ). 



Data were analyzed using analyses of variance (ANOVA) on 

 logio («+ 1) transformed data; the log transform was used to 

 normalize the data and reduce the dependence of the sample 

 mean and variance (Cassie 1968). Data from 1977 and 1978 

 from stations EB-B and EB-C were analysed by four-way 



1 Raytheon Company, P.O. Box 360, Portsmouth, RI 0287 ] . 



'Raytheon Company, P.O. Box 360, Portsmouth, Rhode Island; present 

 address: 124 North Road, Kingston, RI 02881. 



'Yankee Atomic Electric Company, 1671 Worcester Road, Framingham, MA 

 01701. 



4 Reference to trade names does not imply endorsement by Raytheon Co. 

 or by the National Marine Fisheries Service, NOAA. 



'Snooks, J. H., and J. P. Jacobson. 1979. Currents and residual drift in 

 Block Island Sound during the period February through December 1978. 

 Yankee Atomic Electric Company Report YAEC-1149 submitted to New Eng- 

 land Power Co., 20 Turnpike Rd., Westborough, MA 01581. 



15 



