appeared approximately 4 wk after the first stage I larvae was 

 found, while at station 3 the corresponding development period 

 lasted more than 5 wk possibly due to lower mean surface 

 water temperature at this site. Average surface temperatures 

 were 15.0°C and 16.2°C at stations 3 and 2, respectively, dur- 

 ing the period of larval occurrence. At both stations the ap- 

 pearance of stage IV larvae accompanied by the absence of 

 stage I larvae in late July, signaled the end of the spawning 

 period. The single stage IV larva collected on 31 August was 

 attributed to a random late hatch. 



Salinities of 19.4%o or less are unfavorable to larval growth 

 (Templeman 1936). Scarratt and Raine (1967) have shown lar- 

 val avoidance of salinities as low as 21 .4%o. Station 1 was sub- 

 jected to frequent periods of low salinity caused by freshwater 

 runoff from the Penobscot River, possibly explaining the 

 absence of larvae at this site. Larvae may have avoided lower 

 salinity surface water at station 1 and were therefore not vul- 

 nerable to neuston gear. 



It is well documented that early stage I lobster larvae exhibit 

 positive phototaxis (Hadley 1908; Herrick 1911; Ennis 1973), 

 concentrating in the near-surface waters during daylight. 

 However, young larvae are subject to mortality from ultra- 

 violet radiation (Huntsman 1924; Templeman 1936) and tend 

 to move from surface waters during periods of bright sunlight 

 (Templeman and Tibbo 1945). Based on cloud cover observa- 

 tion recorded during the present study it appeared that the 

 larvae adjusted their depth in response to ambient light inten- 

 sity. Larvae apparently moved to surface waters during 

 partially to totally overcast days when sunlight intensity was 

 reduced. During periods of high light intensity, lobster larvae 

 may have descended to avoid possible harmful levels of ultra- 

 violet radiation. During periods of intense sunlight, the larvae 

 may have been below the net sampling depth, accounting for 

 the capture of 92% of stage I larvae when cloud cover equaled 

 or exceeded 50%. Stage IV larvae, which are not as susceptible 

 to ultraviolet radiation, were found at the surface on days of 

 <50% cloud cover although the number of stage IV larvae 

 collected was low. 



SUMMARY AND CONCLUSIONS 



Data analysis from this program, designed to study Ameri- 

 can lobster larvae abundance and distribution at three loca- 

 tions in Penobscot Bay, Maine, from May through September 

 1976, revealed the following: 



1) Abundance of American lobster larvae for the three areas 

 of Penobscot Bay studied appeared to be relatively low com- 

 pared with Canadian waters such as the Northumberland 

 Strait and various New England areas. 



2) The hatching period for the American lobster in Penob- 

 scot Bay extended over a 6-wk period from mid-June through 

 late July in 1976 when coastal water temperatures rose more 

 rapidly than in previous years, resulting in a correspondingly 

 early hatching period. 



3) Low average salinities as found in surface waters near 

 station 1 in early summer may have been detrimental to larval 

 development resulting in either the avoidance of the area by 

 larvae or mortality of larvae. 



4) Early planktonic stages which are more vulnerable to 

 ultraviolet radiation than stage IV larvae were most abundant 

 in the near-surface waters on cloudy days. 



ACKNOWLEDGMENTS 



We thank Environmental Studies Department personnel from 

 the Searsport, Maine, field station who assisted in various ways. 



LITERATURE CITED 



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