at Boothbay Harbor during the period of peak larval density in 

 the Gulf of Maine. Larvae were collected at water tempera- 

 tures ranging from 12.5° to 28.5 °C in Long Island Sound with 

 peak hatching occurring at approximately 20°C (Lund and 

 Stewart 1970). 



Hughes and Matthiessen (1962) reported intensive hatching 

 activity at approximately 15 °C at a culture facility supplied 

 with ambient running seawater. Hatching occurred at temper- 

 atures as low as 9.4 °C and peak hatching was noted at 20 °C. 

 The time required to reach the fourth larval stage varied in- 

 versely with water temperature, ranging from 9 to 33 d ai 

 mean water temperatures of 22.3°-16.1 °C. 



Templeman (1936) reported the cumulative time required to 

 reach successive larval stages (I-V) at temperatures ranging 

 from 7° to 24°C. At 15°C approximately 25 d were needed (o 

 reach the fourth larval stage while an increase to 20 °C reduced 

 the time required to reach stage IV to 13 d. These data are 

 extremely useful in correcting density estimates for intermolt 

 duration (Scarratt 1964, 1973). The graphical presentation 

 of Templeman (1936) was therefore converted to a series of 

 of power curves relating intermolt period to water tempera- 

 ture for each larval stage (Table 2). 



Table 2. — Parameter estimates and degree of fit index for the relationship I) - 

 aT where D and T represent stage duration (da>s) and temperature (°C), re- 

 spectively. Equations derived from the graphical presentation of Templeman 

 ( 1936) b> calculating the difference between the cumulative limes required to reach 

 successive larval stages and regressing on temperature. 







Larval 



stage 





Parameter 



I 



II 



III 



IV 



a 

 b 

 R- 



1.123.542 

 -1.91255 

 .968 



2,510.476 

 -2.16334 

 .967 



2,745.043 

 - 2.07060 

 .970 



7,492.117 

 -2.11708 

 .958 



larval lobster distribution and inferred that passive transport 

 may affect catch rates of later stage larvae. However, in an 

 analysis of the same data, Caddy (1979) computed centers of 

 density for each stage within the survey area and concluded 

 that larvae may move against the prevailing surface drift, 

 presumably by vertical migration and transport by subsurface 

 countercurrents. Scarratt (1968, 1969) reported predominately 

 onshore southwesterly winds off Nova Scotia during the 

 period of larval occurrence and suggested that larvae may be 

 concentrated along windward coastal locations by onshore 

 winds. Rogers et al. (1968) noted higher levels of stage I 

 larvae in offshore stations in southern New England while 

 stage IV lobsters dominated inshore stations, implying an 

 onshore drift with time. Coastward surface drift rates of up 

 to 6.4 km/d during the larval period were cited. Evidence 

 for retention of larvae within circulation gyres in western Long 

 Island Sound was presented by Lund and Stewart (1970). 

 Squires (1970) acknowledged the possibility of larval trans- 

 port in surface waters but postulated that larvae may main- 

 tain position during strong winds by descending in the water 

 column. Ennis (1975) indicated that lobster larvae were more 

 sensitive to hydrostatic pressure than light intensity and were 

 capable of depth regulation within broadly defined limits. 

 There was considerable diminution of sensitivity to pressure 

 changes in stage 111 and IV larvae. Harding et al. (1979) re- 

 ported thai higher densities of larvae in central and eastern 

 St. Georges Bay, Nova Scotia, were due to prevailing south- 

 westerly winds in summer. Stasko (footnote 2) postulated that 

 surface circulation patterns would result in advection of larvae 

 from Georges Bank and Browns Bank toward southwest Nova 

 Scotia. Harding et al. (1982) further proposed that creation 

 of convergent zones through Langmuir circulation may result 

 in concentrations of larvae, explaining the generally observed 

 contagious distribution patterns. 



SALINITY 



Scarratt (1968, 1969) noted a distinct onshore-offshore 

 salinity gradient during July-August off Nova Scotia; larval 

 lobster densities tended io be greater at higher salinity sam- 

 pling locations. Scarratt and Raine (1967) reported that firsi 

 stage larvae avoided salinities of < 21.4 ppt in laboratory ex- 

 periments. Templeman (1936) had earlier noted that survival 

 rates were adversely affected at salinities below 20 ppt. Above 

 this level, neither survival nor time required to reach fourth 

 stage was significantlv affected. 



SURFACE CIRCULATION 



Vertical distribution studies indicating low concentrations 

 of lobster larvae in subsurface waters have led to speculation 

 that wind-induced surface circulation patterns may influence 

 larval distribution. Templeman (1937) concluded that offshore 

 winds result in dispersal of larvae in surface waters. Temple- 

 man and Tibbo (1945) integrated the results of drift bottle 

 investigations, wind pattern observations, and larval lobster 

 distribution studies and suggested that surface hydrography 

 determined the spatial distribution of larvae. Scarratt (1964) 

 considered surface circulation to be a primary determinant of 



SURVIVAL 



Estimates of survival between stages I and IV were derived 

 by Scarratt (1964, 1973) after standardizing larval density 

 estimates for stage duration at prevailing water temperatures. 

 Estimated survival rates ranged from 0.79% to 2.39% during 

 1949-61 and averaged 1.12%. Harding et al. (1982) estimated 

 a survival rate of 1.0% through the pelagic phase after ad- 

 justment for stage duration in St. Georges Bay, Nova Scotia, 

 during 1978. Considerably higher estimates of survival 

 (>50%) were calculated by Lund and Stewart (1970) in Long 

 Island Sound; however, no attempt was made to adjust for 

 increased stage duration and availability with successive larval 

 stages. Ennis (1975) cautioned that differential response of the 

 larval stages to varying light levels may bias estimates of 

 survival based on surface plankton hauls. Correction for stage- 

 specific larval response to ambient light levels should allow 

 increased precision in estimates of larval lobster density and 

 survival rates, however, the confounding influence of within- 

 stage variability in phototactic responses (Hadley 1908) greatly 

 complicates development of an appropriate adjustment factor. 

 Estimates of survival based on surface samples should be 

 considered preliminary until further information on the effects 

 of light intensity, wind direction and velocity, and other 

 environmental variables on larval lobster distribution (vertical 

 and horizontal) are quantified. 



