TEMPERATURE 



Marked differences in water temperature at first occurrence 

 of larvae were noted between the Gulf of Maine and southern 

 New England. Bottom water temperatures at hatching were as 

 low as 8°-9°C in samples collected in northern New England 

 but ranged from 11° to 13.6°C in Buzzards Bay and Block 

 Island Sound (Table 2). Bottom water temperatures at peak 

 larval densities were 8.5°-16.0°C in northern and 12.8°-17.0°C 

 in southern areas (Table 2). Surface water temperatures during 

 the period of highest density were approximately 15°-20°C 

 depending on year and area sampled (Table 2). Hatching is 

 presumably keyed to an increase in water temperature during 

 late spring. Annual variation in water temperature during 

 May-October may affect the onset and duration of hatching, 

 intermolt duration, and survival of larvae. 



VERTICAL DISTRIBUTION 



Lobster larvae were consistently found in higher concentra- 

 tions in surface collections in Block Island Sound and Cape 

 Cod Bay (Bibb et al. 1983a; Collings et al. 1983; Lawton et al. 

 1983). Bibb et al. (1983a) reported significantly higher surface 

 densities of larvae during daylight, however, occasional high 

 larval densities were noted in near bottom samples. Lawton et 

 al. (1983) obtained two larvae in 48 subsurface tows at depths 

 ranging from 3.0 to 7.6 m in Cape Cod Bay in 1977. Signifi- 

 cant depth related differences in larval density were observed 

 in Cape Cod Bay with higher abundance at the surface (Col- 

 lings et al. 1983). These results are consistent with the observa- 

 tions of Templeman (1937), Templeman and Tibbo (1945), 

 and Scarratt (1973). 



Discrete depth samples taken within the Cape Cod Canal 

 showed no significant differences with depth (Collings et al. 

 1983); Matthiessen and Scherer (1983) reported significantly 

 higher larval density at 3 m depth at the eastern end of the 

 Canal. The turbulence and mixing effect of water flow 

 through the Canal were cited as possible factors influencing' 

 vertical distribution within the Canal. 



DIURNAL DISTRIBUTION 



Bibb et al. (1983a) noted significantly higher density of lar- 

 vae in daylight surface samples in Block Island Sound; 

 however, substantial numbers of larvae were collected both at 

 the surface and in near-bottom waters at night. Lux et al. 

 (1983) reported decreased surface abundance during darkness. 

 A shift in relative stage composition was also noted. First stage 

 larvae were most abundant during daylight while stage III lar- 

 vae were dominant in night collections. These observations are 

 in accord with known differences in phototactic responses 

 among larval stages (Hadley 1908; Templeman 1936b). 



Reduced abundance of larvae in daylight surface samples 

 was observed under completely overcast conditions (Lawton et 

 al. 1983; Collings et al. 1983). Templeman and Tibbo (1945) 

 speculated that some minimum light intensity was necessary to 

 attract larvae to the surface. Greenstein et al. (1983) reported, 

 however, that 84% of larvae collected in Penobscot Bay in 

 1976 were obtained with cloud cover greater than or equal to 

 50%; 62% of the larval catch was taken on completely over- 

 cast days. Harding et al. (1982) reported that most larvae 

 (95%) were collected in the upper 30 cm of the water column 



during overcast conditions; during bright sunlight, 73.3% of 

 the larvae obtained were within the 0-30 cm depth interval. 

 Differences in turbidity may alter the effect of light intensity 

 on vertical distribution of larvae among geographical locations 

 (Templeman and Tibbo 1945), possibly explaining some of the 

 discrepancies noted above. 



SUMMARY 



Larval stages of the American lobster were collected 

 during May-October in New England investigations during 

 1974-79. Lobster larvae occurred earlier in the southern New- 

 England region than in the Gulf of Maine. Lobster larvae 

 were more abundant in southern New England than in the 

 Gulf of Maine (including Cape Cod Bay). Favorable condi- 

 tions for production of larvae in southern New England (lower 

 mean size at maturity), coupled with the effects of prevailing 

 southwesterly winds which concentrate larvae along windward 

 shores, undoubtedly contributed to higher density estimates 

 in Buzzards Bay and Block Island Sound. 



Unusually high proportions of stage IV larvae, accompanied 

 by reduced densities, were observed in several studies during 

 1978. Increased density dependent survival through the pelagic 

 phase may account, in part, for this result. Alternatively, 

 transport of larvae from offshore locations may have resulted 

 in increased stage IV representation in 1978. 



Larvae were most abundant at the surface during daylight 

 hours and some evidence for dispersal of larvae from surface 

 waters during night was obtained. The diurnal and vertical 

 distributions of lobster larvae are, of course, not independent; 

 however, the apparent concentration of larvae in surface 

 waters during daylight offers clear advantages for the develop- 

 ment of an appropriate sampling design. Lobster larvae are 

 seldom collected in dense concentrations and factors resulting 

 in further dispersal of larvae should be considered in the 

 development of sampling strategies. 



LITERATURE CITED 



AIKEN, D. E., AND S. L. WADDY. 



1980. Maiurily and reproduction in the American lobster. Can. Tech. 

 Rep. Fish. Aquai. Sci. 932:59-71. 

 BIBB, B. G., R. L. HERSEY, and R. A. MARCELLO, Jr. 



1983a. Distribution and abundance of lobster larvae (Homarus ameri- 



canus) in Block Island Sound. U.S. Dep. Commer., NOAA Tech. Rep. 



NMFSSSRF-775:15-22. 



1983b. A comparison of lobster larvae sampling using neuston and Tucker 



nets. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-775:63-64. 



COBB, J. S., and D. WANG. 



In press. Fisheries biology of lobsters and crayfish. In A. J. Provenzano 

 (editor), The biology of Crustacea, Vol. 5: Economic aspects and patho- 

 biology. 

 COLLINGS, W. S., C. COOPER-SHEEHAN, S. HUGHES, and J. L. 

 BUCKLEY. 

 1983. The spatio-temporal distribution of American lobster larvae 

 {Homarus americamts) in the Cape Cod Canal and approaches. U.S. 

 Dep. Commer., NOAA Tech. Rep. NMFS SSRF-775:35-40. 

 FOGARTY, M. J. 



1983. Distribution and relative abundance of American lobster (Homarus 

 americamts) larvae: A review. U.S. Dep. Commer., NOAA Tech. Rep. 

 NMFS SSRF-775:3-8. 

 FOGARTY, M. J., M. A. HYMAN, G. F. JOHNSON, and C. A. GRISCOM. 

 1982. Distribution, relative abundance, and seasonal production of Ameri- 

 can lobster {Homarus americamts) larvae in Block Island Sound 1978. 

 U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-775:23-28. 



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