6.0 km/h (3.25 kn) as determined by electronic log during 

 1977-79. 



Except where there was significant net clogging, the tows 

 were 0.5 h in duration. At 6 km/h the estimated surface area 

 sampled in a 0.5-h tow was 6,000 nr, and the estimated 

 volume of water filtered was 3,000 m\ assuming that the net 

 sampled a surface layer of water 0.5 m deep. At the lower 

 towing speeds used in 1976 the estimated volume filtered in a 

 0.5 h tow ranged from 2,200 to 2,750 m ! . The volume actually 

 filtered may vary considerably depending on depth of the 

 net in the water, extent of clogging, and the amount of wind 

 and wave action (Scarratt 1973). The water volumes filtered 

 that we have used therefore must be considered approximate. 



Where net clogging occurred due to algal blooms or concen- 

 trations of ctenophores the volume filtered was reduced. Tows 

 in which clogging was apparent were abbreviated. Clogging 

 often occurred from mid-July to early August, affecting 

 approximately 10% of the tows in a season. 



At the completion of each tow the catch was removed from 

 the cod end and floating algae and eelgrass were rinsed free 

 of organisms and discarded. The catch then was strained with 

 a sieve, placed in jars, and preserved in 2% formaldehyde; 

 lobster larvae were sorted in the laboratory. 



Weather permitting, all stations were sampled once each 

 week during May-August. In 1977-79 we sampled six stations 

 in two transects, each of which was 9 km in length (Fig. 1). In 

 1976 we sampled only the easternmost transect, which we 

 divided into four stations (Fig. 1). Sampling began at approxi- 

 mately 0800 h (EST) and was completed by about 1400 h. On 

 one occasion, in 1976, we sampled during early evening hours 

 and after dark. 



Surface water temperature was recorded to the nearest 

 0.1 °C at the beginning of each tow, using a mercury thermom- 

 eter. Surface to bottom temperatures were obtained with an 

 electronic probe in 1977 and part of 1978. Wind and cloud 

 cover observations were noted on each tow log. 



RESULTS 



Over the 4 yr sampled, 16,679 larval lobsters were caught, 

 averaging 23.3/1,000 m 3 of water filtered (Table 1). Numbers 

 of larvae varied considerably from year to year with totals 



ranging from 1,284 in 1976, when there were fewer stations, 

 to 10,303 in 1979. 



There was a marked variation also in the composition of the 

 catch by stage of development, both within and between years 

 (Table 1). Stage II predominated in 1976 and 1977; stage IV, 

 in 1978; and stage III, in 1979. The large numbers of stage 

 IV larvae in most years seemed unusual, even though the 

 longer duration of this stage increases the chance of capture. 

 In 1978, when this was most pronounced, there were more 

 than twice as many stage IV larvae as the other stages 

 combined (Table 1). 



Estimates of the abundance of larvae by sampling date for 

 all stations combined in each year (Fig. 2) indicate that the 

 larvae began to appear in the catch in the latter half of May, 

 reached peak numbers in mid to late June, and had completed 

 pelagic stages by early August. The surface water temperature 

 when larvae first were caught was about 13°-15°C; the tem- 

 perature at the bottom usually was 1 ° or 2° lower than at the 

 surface (Fig. 2). The temperature at the peak of larval produc- 

 tion was about 19°C at the surface and 17°C at the bottom. 

 These temperatures for initiation of hatching and peak of 

 larval production agree rather closely with the findings of 

 Hughes and Matthiessen (1962). Water temperatures as high 

 as about 24 °C at the surface were recorded in July and early 

 August (Fig. 2). 



There was no consistent pattern in total abundance by sta- 

 tion, although the largest catches generally were made at 

 station 3 (Fig. 1). The water temperature was higher by about 

 1 -2°C at stations 4-6 (A-D), where the depth was 10-12 m, 

 than at stations 1-3, where the depth was about 15 m, but it 

 was not clear if these temperature or depth differences 

 affected larval abundance. 



The high numbers of larvae caught in 1979 were due largely 

 to catches on one sampling date (18 June) when 6,746 larvae 

 were caught in the five tows (Table 1). The mean total catch 

 per 1,000 m 3 of water filtered for 18 June was 450 larvae (Fig. 

 2). The year 1979 was, however, one of generally high larval 

 abundance in Buzzards Bay (Fig. 2). 



The abundance of lobster larvae by developmental stage for 

 each year and sampling date show the general progression of 

 stages through the hatching season (Fig. 3). The abundance 

 of stage 1 larvae usually peaked around mid-June and stage 

 IV peaked in late June. Larvae were caught from late May to 



Table 1. — Total numbers of tows, numbers of tows containing larval lobsters, total numbers of 

 lobster larvae of each stage, mean total numbers per 1.000 m\ and percentage frequencv by stage 

 (in parentheses) for Buzzards Ba\ neuston sampling in 1976-79 and all vears combined. 





Number 



of tows 



Numbers of larv 



ae of each 



stage 



Total 









With 



per 



Year 



Total 



larvae 



I 



II 



III 



IV 



number 



1,000 m' 



1976 



50 



32 



433 



484 



290 



77 



1.284 



10.1 









(33.7) 



(37.7) 



(22.6) 



(6.0) 



(100.0) 





1977 



80 



56 



706 



1,064 



759 



932 



3.461 



18.8 









(20.4) 



(30.8) 



(21.9) 



(26.9) 



(100.0) 





1978 



62 



41 



90 



103 



243 



1,195 



1.631 



9.6 









(5.5) 



(6.3) 



(14.9) 



(73.3) 



(100.0) 





1979 



88 



56 



2,413 



2,640 



3,962 



1,288 



10,303 



43.7 









(23.4) 



(25.6) 



(38.5) 



(12.5) 



(100.0) 





All vears 



280 



185 



3.642 



4.291 



5,254 



3,492 



16,679 



23.3 









(21.8) 



(25. "I 



(31.5) 



(21.0) 



(100.0) 





30 





