Table 1. — Schedule, stations, gear type, and procedures for lobsler larvae sampling in western Cape 



Cod Bay, 1974-77. 



Year 



Sampling 

 dates 



Station 

 locations 

 (Fig. 1) 



Gear type 



x Tow 



duration 



(min) 



x Volume of 

 water sam- 

 pled (m>) 



x Tow 



speed 

 (km/h) 



1974 



5/24-8/20 



7-10 



1 x 2 m 

 neuston net 



11.5 



- 



3.7 



1975 



5/23-8/5 



3, 5, 11, 12, 13 



1 X 2 m 

 neuston net 



30 



3,774 



4.6 





6/20-8/14 



A-D 



two 1 x 1 m 

 neuston nets 



10 



1,400 



3.5 



1976 



6/4 -8/11 



1-6 



1 x 2 m 

 neuston net 



30 



3,271 



4.6 



1977 



5/5 -8/10 



1-6 



1 x 2 m 

 neuston net 



30 



3,001 



4.6 





6/9 -8/1 



5-6 



1 x 1.5 m 

 Tucker trawl 



20 



1,301 



5.6 



examined for larvae, and discarded. If large amounts of algae, 

 and/or eelgrass, Zostera marina, were present, a third rinse 

 was performed to assure complete removal of larvae. Contents 

 washed into the 1 .05 mm sieve were transferred into labeled 1 

 litre jars containing a preservative of 5% buffered Formalin- 

 seawater solution. Samples were sorted in the laboratory, and 

 lobster larvae were identified and enumerated by molt stage 

 according to Herrick (1911). 



Sampling Stations, Schedule, and Data Analysis 



Location of sampling stations is presented in Figure 1 . We 

 conducted neuston sampling on a biweekly basis in 1974 and 

 1975 (Table 1). Weekly collections were made in 1976. Bi- 

 weekly sampling in May and June 1977 was intensified to 

 several days each week in July and August during peak hatch- 

 ing. In June 1977, we initiated biweekly subsurface towing 

 at stations 5 and 6 at depths of 3.0 m, 5.5 m, and 7.6 m. In 

 July and August, we increased the frequency of sampling to 

 weekly intervals. We collected data until ctenophore abun- 

 dance precluded successful net operations in early August. 



The effect of local wind conditions on the concentration 

 of lobster larvae was examined in 1975 and 1976. Mean weekly 

 wind speed, direction, and duration at Pilgrim Station were 

 determined from data provided by Boston Edison Company. 

 Data were grouped into 16 wind directions and by 8.0 km/h 

 wind speed increments. 



Density estimates for each larval stage were corrected for 

 stage duration according to Templeman (1936) for each 

 sampling date. Differences in stage I and stage IV density 



(no./ 1,000 m 3 ) by station were examined by Kruskal-Wallis 

 tests (Sokal and Rohlf 1969). 



RESULTS 



1974 Sampling 



We collected only 25 lobster larvae in 1974 (Table 2) in the 

 vicinity of the power plant (Fig. 1). Only nine tows contained 

 larvae. The first larva was obtained on 2 July and was in the 

 fourth stage. Only one first stage larva was found, with other 

 collections consisting exclusively of stage IV individuals. The 

 maximum number (7) captured in one tow was collected at 

 station 7 on 7 August. 



1975 Sampling 



Expanded spatial coverage in 1975 yielded a total of 177 

 lobster larvae (excluding shoal water stations A-D). Larvae 

 were first collected on 10 June at stations 12 and 13 (Fig. 1). 

 All were first stage, indicating that hatching had just com- 

 menced. On this date, water temperatures in western Cape 

 Cod Bay averaged 14.8 °C at the surface and 12.7 °C on the 

 bottom (Fig. 2). As determined by the presence of stage I 

 larvae in our catch, the hatching period extended from 10 June 

 into the first week of August, or approximately 56 d. Densi- 

 ties of all stages peaked in early July when a total of 137 larvae 

 (65% stages I and II) was captured on one sampling date. The 

 largest number of larvae was collected at station 3 on 8 July. 



Table 2. — Larval catch, mean densities, and percent composition for stages I-IV collected in neuston tows in 

 western Cape Cod Bay, 1974-77. 











Percent catch 













Bottom 





composition 





Avg. 







No. 

 tows 



temperature 

 range (°C) 





by molt 



stage 





density 

 (No. /1,000 m') 



Total larval 



Year 



I 



11 



III 



IV 



catch 



1974 



20 







4.0 







96.0 







25 



1975 



27 



7.7-14.8 



59.9 



23.7 



8.1 



8.3 



2.05 



177 



1976 



60 



5.5-16.5 



25.5 



19.7 



29.6 



25.2 



4.44 



871 



1977 



78 



5.5-15.0 



55.2 



16.9 



5.3 



22.6 



1.26 



206 



49 



