Distribution and Relative Abundance of American 

 Lobster, Homarus americanus, Larvae: A Review 



MICHAEL J. FOGARTY 1 



INTRODUCTION 



The American lobster, Homarus americanus, is among the 

 most valuable fishery resources of the east coast of the United 

 States. Preliminary U.S. landings of American lobster in 1980 

 were 16,800 metric tons (t) with an estimated ex- vessel value of 

 $75 million (National Marine Fisheries Service 1980). Intensive 

 exploitation of this valuable resource has resulted in concern 

 over possible impacts of increasing fishing mortality rates on 

 yield and reproductive potential of inshore populations 

 (Anthony and Caddy 1980). Despite large-scale research ef- 

 forts to define the population dynamics of the American lob- 

 ster, relatively little is known about the determinants of larval 

 production, survival, and subsequent recruitment to the fish- 

 eries. Observations on the occurrence of larval American 

 lobsters have been documented since the latter part of the 19th 

 century (Smith 1873; Herrick 1896); however, quantitative 

 sampling programs have been undertaken only within the last 

 30 yr. 



Larval development of the American lobster is characterized 

 by four pelagic instars. A brief prezoeal stage precedes the first 

 larval stage (Davis 1964). Hatching primarily occurs during 

 late May-early June in New England (Hughes and Matthiessen 

 1962) after a 10-1 1 mo incubation period. Larvae typically oc- 

 cur in the plankton from late May to early September depend- 

 ing on location. The larval phase is normally completed in 

 25-35 d although stage duration is temperature dependeni 

 (Templeman 1936). Settlement occurs during the fourth larval 

 stage (Scarratt 1973) and the postlarvae are benthic. 



In this review, the distribution and relative abundance of 

 larval lobsters in relation to depth, hydrographic factors, and 

 environmental variables are summariezed and additional in- 

 formation on survival rates and stock-recruitmeni relation- 

 ships examined. Phillips and Sastry (1980) reviewed aspects of 

 larval lobster behavior, physiology, nutritional requirements, 

 and ecology. Stasko (1980) and Fair (1980) provided sum- 

 maries of Canadian and U.S. investigations on the distribution 

 of larval American lobsters in the northwest Atlantic. 



VERTICAL DISTRIBUTION 



Several studies have indicated that lobster larvae are concen- 

 trated at the surface during daylight. Templeman (1937) re- 

 ported that daytime catch rates at the surface were six-fold 

 greater than at 0.2-4.5 m depth and no lobster larvae were 



Rhode Island Department of Environmental Management, 150 Fowler 

 Street, Wickford, R.I.; present address: Northeast Fisheries Center Woods Hole 

 Laboratory, National Marine Fisheries Service, NOAA, Woods Hole, MA 

 02543. 



obtained at 5.5-11 m. Smith (1937 cited by Stasko 1980) 

 reported catch rates of 10.0 larvae/tow in surface samples 

 and 0.9 larvae/tow at subsurface depths; larvae in subsur- 

 face hauls were primarily collected at night or at dawn. Tem- 

 pleman and Tibbo (1945) concluded that larvae were primarily 

 neustonic in the Gulf of St. Lawrence, however, ambient 

 light levels were found to affect depth distribution and this 

 effect varied with larval stage. In the Gulf of Maine, Sherman 

 and Lewis (1967) reported that catches in surface tows ex- 

 ceeded those in oblique hauls (0-20 m) by a factor of 2.4. 

 Scarratt (1973) noted sharp differences in daytime catch rates 

 between neuston and subsurface nets suspended at 0.6-1.2 m 

 depth; in two series of hauls (34 tows), 876 larvae were 

 obtained in the upper net and 95 in the lower. Further samples 

 taken at 4-18 m depth (13 tows) yielded 14 larvae and no larvae 

 were obtained in tows with the net held 10 cm from the bot- 

 tom. Stasko ; reported that few lobster larvae were taken in 

 subsurface collections on the Scotian shelf. Harding et al. 

 (1982) sampled the upper 1 10 cm of the water column with a 

 three compartment net; 81.4, 14.1, and 4.5% of the larvae 

 obtained were within the 0-30, 30-70, and 70-110 cm depth 

 sirata, respectively. 



LIGHT INTENSITY 



Ambienl light intensity has been demonstrated to influence 

 ihe venical distribution of lobster larvae. Templeman (1937) 

 concluded on the basis of field observations that first and 

 second stage larvae react positively to low intensity light but 

 respond negatively to increased light intensity. Templeman 

 and Tibbo (1945) noted that third and fourth stage larvae are 

 less sensitive to light levels than earlier stages. Diurnal vertical 

 disiribution was apparently related to light intensity and larvae 

 tended to disperse from surface waters during night except 

 under bright moonlight (Templeman 1939). Scarratt (1973) 

 demonstrated significantly higher catch rates at the surface for 

 stage I larvae during daylight, however, no significant dif- 

 ferences between day and night samples were observed for 

 second stage larvae. Positive phototaxis was noted for first and 

 second stage larvae under experimental conditions, however, 

 sustained phototactic behavior was not observed and later 

 stage larvae were less responsive to changes in light intensity 

 (Ennis 1975). Harding et al. (1982) noted a dispersal from sur- 

 face (0-30 cm) waters during bright sunlight, confirming the 

 observations of Templeman and Tibbo (1945). 



Early observations under laboratory conditions indicated 

 that phototactic responses differed among larval stages and. 



-Stasko, A. B. 1977. Lobster larvae on [he Scoiian Shelf. Can. Atl. Fish. 

 Sci. Adv. Comm. Res. Doc. 77/31. 10 p. 



