Table 4. — Mean density and standard deviation per 1,000 m i of lobster 

 larvae by stage collected along four transects in Block Island Sound 

 during May and June 1979. 









Stage 







I 





11 



III 



IV 



Transect 



Mean 



SD 



Mean SD 



Mean SD 



Mean SD 



Weekapaug 



2.9 



3.3 



1.5 2.2 



0.1 0.3 







East Beach 



4.9 



7.2 



1.6 2.3 



0.4 0.8 







Nebraska 













Shoals 



7.7 



8.3 



1.3 1.8 



0.2 0.4 







Point Judith 



16.4 



23.6 



2.0 4.1 



0.5 1.0 







Observations on surface current patterns indicate westward 

 surface currents from the Point Judith area (Fig. 7), suggest- 

 ing transport of larvae to the west. 



Production 



Relative production for the 1977 and 1978 seasons was de- 

 termined using the method of Scarratt (1964). Weekly produc- 

 tion was divided by the time between molts (Templeman 1936) 

 for each stage at the corresponding mean surface temperature 

 for that week. Weekly production estimates were then summed 

 to estimate relative seasonal production. The estimated 

 seasonal production of lobster larvae in 1977 was threefold 

 higher than the 1978 production estimate (Table 5). There was 

 an exponential decrease in production from stages I and IV in 



1977. Stage II abundance was40°7o of stage 1; stage 11 was 57°7o 

 of II; and stage IV as 33% of III. A similar pattern was ob- 

 served for stages I, II, and III in 1978. However, in 1978, stage 

 IV production exceeded that of stages II and III. 



DISCUSSION 



Lobster larvae in Block Island Sound were abundant in 

 the plankton for a relatively short period in June and July. 

 Observation of stage I lobster larvae in late May or early June 

 is an indication of recent hatching. Since the duration of stage 

 I is approximately 1 to 5 d (Herrick 1911), first hatching oc- 

 curred off East Beach in mid to late May during 1977-79. The 

 duration of hatching activity was about 8 to 9 wk based on 

 the occurrence of stage I larvae in the water column. Peak 

 hatching apparently occurred in mid to late June in 1977-79. 



Herrick (1911) observed that hatching was triggered by 

 rising temperatures. The bottom temperature when larvae 

 were first observed off East Beach was 13.3 °C in 1977, 13.6°C 

 in 1978, and 12.6°C in 1979. Peak abundance of stage I larvae 

 occurred in early June in 1977 and 1979 and in early July in 



1978. This reflects a later warming trend in 1978. In 1977 and 



1979. bottom temperatures at EB-B had reached 12 °C by 

 about 20 May; in 1978, water temperatures did not reach this 

 level until 30 May. Bottom temperatures during periods of ap- 

 parent maximum hatching were approximately 14°-18°C. 

 Peak occurrence of stage I larvae was observed at tempera- 

 tures of 13°-15°C in Maine by Sherman and Lewis (1967). In- 

 tensive hatching was observed in Martha's Vineyard at tem- 

 peratures of 15°-20°C by Hughes and Matthiessen (1962). 



Hatching was apparently complete by early August in both 



1977 and 1978. Stage IV larvae were observed from mid-June 

 until the last week of August in 1978, but only from late June 

 until the first week of August 1977. 



Templeman (1939), Scarratt (1973), and Sherman and Lewis 

 (1967) observed highest surface concentrations of lobster 

 larvae during daylight. Our results generally confirm these 

 observations. On occasion, considerable numbers of stage I 

 larvae were caught in near-bottom waters during both day and 

 night. 



The distribution of lobster larvae observed in 1977 and 



1978 suggests a hatching area near stations EB-C and EB-D. 

 Larvae which hatch in this area may be transported westward 

 and collected at stations EB-C and EB-D. 



Currents in Block Island Sound are primarily tidal, with 

 eccentric elliptic patterns generally parallel to the shore (east- 

 west). Velocities are moderate to strong (0.15 to 0.30 m/s). 

 Residual drift is strongly influenced by local winds with strong 

 seasonal variability (Snooks and Jacobson footnote 5). Sur- 

 face drifters released at stations off East Beach and other 

 Block Island stations in July 1977 were all recovered along 

 the mainland shore to the west of the release point except for 

 those released just off Block Island; some of these were re- 

 covered off Block Island and Long Island (Fig. 7). 



The 1979 study was designed to identify hatching sites in 

 Block Island Sound and their potential contribution to lobster 

 populations off East Beach. However, the 1979 results are of 

 limited use in identifying hatching areas because the sampling 

 period was abbreviated. Nevertheless, several factors point 

 to a major hatching area near Point Judith. Surface drifters 

 indicate transport to the west during summer. Stage I larvae 

 were more abundant in this area (PJ and NS transects). The 

 proportion of stage I larvae was highest along these transects, 

 with higher proportions of stage II and III larvae observed at 

 more westerly transects. 



A summary of observations on lobster larvae for 1976 

 through 1979 off East Beach in Block Island Sound is pre- 

 sented in Table 6. The time of peak abundance was later in 

 1978, reflecting a slower rise in bottom temperature. Average 

 surface abundance of larvae at its maximum showed consider- 

 able variability, even allowing a factor of two to four for total 

 difference in abundance estimates between neuston and 

 Tucker net samples (Bibb et al. 1983). Abundance of lobster 

 larvae for all stages was higher at offshore stations in 1977. 

 In 1978, stage I through III larvae maintained this pattern, 

 but stage IV larvae were more abundant inshore. In 1976, all 

 stages were more abundant at the inshore station. The high 

 abundance of stage IV larvae in 1978 is perhaps the most re- 

 markable difference among the years of observations, possibly 

 resulting from transport from adjacent areas or differences in 

 survival or sampling efficiency. 



ACKNOWLEDGMENTS 



The authors wish to thank Michael Fogarty for loaning 

 the neuston nets; John H. Snooks, Yankee Atomic Electric 

 Company, for providing the temperature and drifter data; and 

 Mark Ciano, Robert E. Walsh, Warren Johns, Abigail Raine, 

 and the crew of the MV Strider for their contributions to the 

 study. Funding was provided by New England Power Com- 

 pany, Contract No. 24146 to Raytheon Ocean Systems Com- 

 pany, Portsmouth, R.I. 



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