Figure 1. — Lobster larvae stations in Cape Cod Bay sampled in 

 1974-75 (Stations I-VIII) and 1976 (Stations l-X, vertical distribution 

 Station A). 



(1976) to 2 September (1976), stage II larvae from 3 June 

 (1976) to 2 September (1976), stage III larvae from 3 June 

 (1976) to 17 September (1975), and stage IV larvae from 

 18 June (1976) to 28 September (1975). Larvae were most 

 abundant during the months of June, July, and August (Table 

 1). Surface water temperatures recorded when larvae were col- 

 lected ranged between 10.5°C (May 1976) and 21.4°C (July 

 1974). 



Early in the season, highest concentrations of lobster larvae 

 were found in the southern section of Cape Cod Bay (Table 2). 

 A highly significant difference (P<0.01) was found between 

 mean densities at stations I-IV and stations V-VIII (X) over all 

 June sampling dates based on a Mann-Whitney U test (Zar 

 1974). No significant difference (P>0.05) was detected for the 



Table 1. — Cape Cod Bay larval lobster collections by month. 1974-76. 











Mean number 







Year(s) 



Number 



Total 



of larvae 





Month 



sampled 



of tows 



larvae 



per 1,000 m» 



SD 



May 



1976 



62 



61 



0.30 



0.83 



June 



1974-76 



142 



2,005 



3.68 



5.67 



July 



1974-76 



147 



2,340 



3.82 



4.86 



Aug. 



1974-76 



141 



735 



1.65 



2.84 



Sept. 



1975, 1976 



52 



28 



0.17 



0.26 



Table 2. — Mean larval lobster densities, per 1,000 m' of water, over Stations I-IV 

 (northern section) and V- V 111 (or X in 1976) (southern section) by month and year. 





Stations 





'1974 





1975 







1976 





n' 



~x s 



n 



X 



5 



n 



x s 



June 



I-IV 



4 



0.82 0.69 



16 



2.82 



2.73 



20 



1.78 2.08 





V-VIII(X) 



2 



1.53 0.38 



16 



6.14 



9.80 



30 



4.80 6.33 



July 



I-IV 



8 



2.60 2.09 



20 



1.09 



2.30 



16 



7.10 5.95 





V-VIII(X) 



8 



2.39 1.93 



20 



2.66 



5.16 



30 



3.85 4.30 



Aug. 



I-IV 



8 



0.87 0.90 



16 



1.17 



1.82 



16 



1.55 1.79 





V-VIII(X) 



8 



1.01 0.81 



16 



2.31 



3.29 



24 



2.03 3.54 



'Although included, little data were available for June 1974 since sampling 

 did not begin until 20 June and Stations VII and VIII were not sampled until 

 July. 



*n = number of samples not including replicate tows which were averaged 

 w ithin dates for each station. 



months of July and August. Although collections were made 

 in May of 1976, few larvae were taken during that period 

 (Table 1). Those that were collected were found in both north- 

 ern and southern areas of the Bay. Small numbers of larvae 

 were also taken in September 1975 (Table 1); most were found 

 in the northern section of the Bay. 



Annual Variations in Abundance 



Average larval densities were compared by month for each 

 year, 1974-76, to determine if any clear differences in abun- 

 dance occurred between years. To make this comparison more 

 valid, stations IX end X, sampled only in 1976, were excluded. 

 Comparisons were based on unadjusted mean densities and on 

 mean densities calculated after dividing each density estimate 

 by the temperature-related stage duration for each larval stage 

 obtained from Templeman (1936). Both the unadjusted and 

 adjusted mean densities suggested that larvae were less abun- 

 dant in 1974 than in 1975 and 1976 (Table 3). The differences 



Table 3.— Mean monthly densities of lobster larvae, per 1,000 m' of water, over 

 Stations I-VIII, for June, July, and August, 1974-76. Mean densities are also 

 shown based on data adjusted for variations in stage duration (see text). Between- 

 station standard deviation in parentheses. 



Month 



Year 



1974 



1975 



1976 





June 



July 



August 



June-August 



No. sampling 



1 



2 



2 



5 



periods 











Mean/ 1, 000 



1.1(0.7) 



2.4(1.4) 



0.9(0.6) 



1.5(1.2) 



Adjusted 



0.2(0.1) 



0.6(0.3) 



0.1(0.04) 



0.3(0.3) 



mean 











No. sampling 



4 



5 



4 



13 



periods 











Mean/ 1,000 



4.5(4.2) 



1.9(1.3) 



1.9(1.0) 



2.7(2.8) 



Adjusted 



0.8(0.6) 



0.4(0.3) 



0.3(0.2) 



0.4(0.4) 



mean 











No. sampling 



5 



5 



5 



15 



periods 











Mean/ 1,000 



3.3(2.5) 



5.8(3.6) 



1.3(0.9) 



3.5(3.1) 



Adjusted 



0.5(0.4) 



1.2(0.8) 



0.3(0.2) 



0.7(0.7) 



mean 











42 



