Mean size at maturity of female lobsters is considerably 

 lower in the warmer waters of southern New England (Van 

 Engle 1980; Aiken and Waddy 1980), resulting in an increased 

 probability of spawning prior to capture. Templeman (1936a) 

 noted an inverse relationship between size at sexual maturity 

 and water temperature in the Canadian Maritime Provinces. 

 Higher brood stock levels may therefore contribute to higher 

 larval lobster density in southern New England waters. It 

 should be noted, however, that the primary source of lobster 

 landings off the northeastern United States is within the Gulf 

 of Main, implying adequate larval production or transport 

 from other areas. 



An association between larval lobster abundance and the 

 occurrence of cencentrations of detached macroalgae and 

 marine vascular plants (primarily spartina) was observed 

 off New Hampshire (Grabe et al. 1983). Larvae may avoid 

 predators by seeking refuge in windrows of drifting vegeta- 

 tion. Wind speed and direction may indirectly influence larval 

 lobster distribution by affecting the formation and distribu- 

 tion of windrows. Harding et al. (1982) reported a significant 

 relationship between the occurrence of lobster larvae and 

 floating vegetation in Si. Georges Bay, Nova Scoiia, Cobb and 

 Wang (in press) have suggested ihc use of artificial seaweed 

 collectors lo moniior abundance of American lobster larvae. 



ANNUAL VARIATION IN ABUNDANCE 



Despite apparent differences between areas in the availabil- 

 ity (catchability) of larvae, relative differences in mean annual 

 density were generally consistent in years for which compari- 

 sons were possible(Fig. 2). Increased density in 1977 relative to 

 1976 and 1978 was noted by Collings et al.(l983) in Cape Cod 

 Bay and Buzzards Bay and by Lux et al. (19S3) in Buzzards 

 Bay. Bibb et al. (1983a) reported decreased abundance in 1978 

 from 1977 density estimates. Matthicssen and Schercr (1983) 



and Lawton et al. (1983) reported increased relative abundance 

 in 1976 over 1975 levels. Lux et al. (1983) observed a sharp 

 increase in mean density in 1979, although this increase was 

 primarily due to several large catches of stage I larvae. In con- 

 trast, Grabe et al. (1983) reported slightly reduced larval den- 

 sity in 1979 relative to the 1978 level, however, the number of 

 larvae obtained was low, possibly obscuring trends in relative 

 abundance. 



A striking increase in the proportion of stage IV larvae was 

 observed in 1978 (Table 2). This shift in stage composition was 

 accompanied by generally reduced density levels (Table 2). In- 

 creased stage IV composition may reflect an increase in sur- 

 vival through the pelagic phase, accentuated by the longer in- 

 termolt duration of fourth stage larvae and hence greater 

 vulnerability to capture (Scarratt 1964, 1973). Positive 

 phototactic responses in early stage IV larvae (Hadley 1908; 

 Templeman 1936b) may render this stage more accessible to 

 capture by neuston gear. However, stage I larvae are also in- 

 itially positively phototactic (Hadley 1908; Templeman 1937; 

 Scarratt 1973). In addition, production estimates with explicit 

 correction for stage duration still exhibited unexpectedly high 

 stage IV densities (Bibb et al. 1983b: Fogarty et al. 1983). 

 Transport of later stage (III and IV) larvae toward inshore 

 locations in wind-induced surface currents and favorable 

 sampling conditions may also have contributed to increased 

 proportions of stage IV larvae in 1978. 



In general, the proportion of stage IV larvae in our studies 

 exceeded those reported by Scarratt (1964, 1973) for North- 

 umberland Strait where the average percentage of fourth stage 

 larvae (uncorrected for stage duration) during 1948-63 was 

 <5 lr o. It is possible that the higher towing speeds in many of 

 the investigations in New England during 1974-79 resulted in 

 the capture of proportionately more stage IV larvae. Increased 

 development of swimming and escape responses in fourth 

 stage larvae may allow avoidance of nets towed at low (<2 

 km/h) speed. 



Figure 2. — Mean annual density (daytime surface lowsl of American lobster lanae in New England studies during 1974-79. 

 Years of sampling indicated al base. Cape Cod Canal estimates not included since unusual hydrographic features of the 

 Canal may result in biased estimates of density. 



12 



