Table 4. — Lobster larvae densities (number per 1,000 m') in vertically stratified 

 Tucker net samples. 





Time 



Surface 





Depth (m) 







Date 



3 



6 



9 



12 



Mean 



7 June 



1437-1700 







1.6 















0.32 



8 June 



0055-0240 



0.73 



4.0 



0.43 











1.03 





0310-0500 



9.99 



27.13 



12.30 



2.36 



3.01 



10.96 



10 June 



1605-1750 



0.34 



















0.07 





1810-2000 



0.40 



0.62 



1.74 



1.55 



0.50 



0.96 



11 June 



0425-0615 



0.56 



2.69 



0.33 



1.24 







0.96 





0715-0850 



0.84 



18.50 















3.87 



19 June 



2345-0100 



49.49 



62.29 



10.88 







0.93 



24.72 





0135-0355 



1.17 



2.16 



0.81 



0.59 



1.09 



1.16 





1105-1240 







0.87 



0.41 



3.30 



0.33 



0.98 





1330-1515 







2.72 



5.09 



1.90 



0.93 



2.13 



23 June 



0215-0410 







0.55 



0.47 



0.91 



0.48 



0.48 





0458-0645 



2.27 



7.95 



2.71 



3.35 



2.21 



3.70 





1430-1635 



0.42 







0.41 











0.42 





1700-1835 



























30 June 



0720-1020 



0.76 



0.79 







1.03 







0.52 





1050-1230 



0.35 



5.49 



1.54 



2.72 



1.01 



2.22 





1940-2135 





























2155-2345 



3.11 



5.26 



2.76 



1.90 







2.61 



7 July 



1355-1538 







0.32 



0.34 











0.13 





1605-1740 















0.73 







0.15 



8 July 



0115-0255 





























0320-0505 



























Mean 





3.06 



6.21 



1.75 



0.94 



0.46 





SD 





10.34 



13.87 



3.35 



1.12 



0.79 





the area under the curve by trapezoidal integration, it was 

 estimated that approximately 7.3 million larvae entered the 

 Bay from the Canal during this 24-d period alone. 



Although the fate of these larvae upon entering the Bay is 

 unknown, information on the hydrography of Cape Cod Bay 

 combined with the available field data for 1974-76 suggest 

 the possibility that many of these larvae entering from the 

 Canal may eventually settle in the area of Provincetown or 

 perhaps pass out of the Bay completely before terminating 

 their pelagic period. Drift bottle studies described by Bigelow 

 (1924) indicate a counterclockwise direction to the Bay surface 

 currents, which, according to Ayers (1956), have an average 

 speed of 1.9 n.mi./d. At this rate, it might require a period 

 of 10 d for stage I larvae originating at the Canal mouth to 

 arrive in the area of Provincetown. Although the duration 

 of the larval period varies strongly and inversely with tempera- 

 ture (Templeman 1936; Hughes and Matthiessen 1962), the 

 fact that 22 d may be required for a newly hatched larva to 

 attain stage IV at 15 °C (Sherman and Lewis 1967) indicates 

 that most of these larvae would not have settled out prior to 

 reaching Provincetown. 



Assuming a counterclockwise drift of the larvae, their pro- 

 jected path from the Canal mouth should pass near Stations 

 VI and then IV prior to passage from the Bay or settlement in 

 the vicinity of Provincetown. This route is suggested by the 

 data in Figure 2 for 1975 and 1976, during which the percent- 

 age of stage I larvae in the samples steadily dropped in a north- 



easterly direction, i.e., between Stations X and VI and between 

 Stations VI and IV. This might explain why stage III larvae 

 were most abundant at Station IV in 1974. 



There is some evidence from the 1976 data that a counter- 

 clockwise current as described by Bigelow (1924) may also 

 serve to transport larvae from the northwest section of the Bay 

 (Station I) into the southwest sector, notably during the month 

 of July. Large concentrations of early stage larvae found at 

 Station 1 in 1976 were followed by high concentrations of lar- 

 vae of later stages at Station VII later during the month (Fig. 

 2). 



The observed vertical distribution of larvae near the mouth 

 of Cape Cod Canal is interesting since most previous efforts 

 to sample larvae have generally relied upon neuston nets in the 

 belief that larvae tend to concentrate at the surface (Lund 

 and Stewart 1970; Scarratt 1973). We suspect, however, that 

 the strong turbulence apparently characteristic of Cape Cod 

 Canal may influence the vertical distribution of the larvae in 

 this area. 



ACKNOWLEDGMENT 



We are grateful to K. Sherman and the journal reviewers 

 for contributing to the manuscript. This work was conducted 

 for and supported by Boston Edison Company as part of a 

 monitoring program for the Pilgrim Nuclear Power Station. 



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1969. A new midwater trawl for sampling discrete depth horizons. J. 

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SCARRATT, D. J. 



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1936. The influence of temperature, salinity, light and food conditions on 

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45 



