Larvae live in the water column and juvenile and adult lobsters in the 

 subtidal zone on unconsolidated and rocky bottoms. Adults and juveniles are 

 most abundant on bottoms that provide shelter in the form of rock crevices 

 (rock bottom), plant life (aquatic beds), or the potential to dig a burrow 

 (unconsolidated bottoms). These shelters partially protect the lobster from 

 predation and from aggression from other lobsters. 



Factors of Abundance 



Natural factors that contribute to fluctuations in lobster populations include 

 predation, disease, and environmental factors. Highest natural mortality 

 rates occur among larvae and juveniles. Larvae are preyed upon by surface- 

 feeding fish such as lumpfish, while juveniles are preyed upon by small 

 bottom- feeding fish, such as the cunner. Larger bottom-feeding fish (such as 

 cod, skates, and sharks) prey on adult lobsters. 



Salinity limits the distribution of lobsters in the characterization area. 

 The lowest salinity tolerance in the laboratory was 13.8 ppt for larvae and 8 

 ppt for juveniles and adults (Cobb 1976). Under natural conditions, lobsters, 

 particularly larvae, probably avoid areas where the salinity is lower than 

 approximately 20 ppt. 



Lobsters may limit their own numbers, also, but the extent of this is unknown. 

 Lobsters are very territorial, aggressive, and cannibalistic. Mortality due 

 to aggressive behavior is probably higher on bottoms that do not have shelter, 

 i.e., crevices in rocks or sediments where lobsters can burrow. 



The species is susceptible to several fatal diseases at various stages in its 

 life cycle. In the larval stage, Leucothrix mucor (a filamentous bacteria) 

 collects in the gill membranes and suffocates the organism, and a fungus, 

 Lagendinium sp., breaks down larval tissues. Another fungus, Haliphthoros 

 milfordensis , infects juveniles and breaks down their shells, exposing more 

 vulnerable inner layers. The most common disease in adults is gaffkemia, or 

 "red tail," which is a bacterial (Aerococcus viridians homari) infection of 

 the blood. The infection begins in an open wound usually inflicted by 

 fishermen in the process of plugging the claws (immobilizing the claw with a 

 wooden plug to stop cannibalism) or in notching berried (egg-carrying) 

 females. These diseases may occur more frequently in lobsters that are kept 

 in enclosed areas, such as containers (for aquaculture) or lobster pounds. 

 Crowding of lobsters and unsanitary conditions increase the incidence and 

 magnitude of disease. 



The highest natural mortality rate in lobsters occurs after molting, before 

 the shell hardens. Besides being vulnerable to predation, lobsters are also 

 subject to aggressive attacks, usually for territorial reasons, by other 

 lobsters that are not in the process of molting and have hard shells. Also, 

 lobsters in the molting stage have been found to be less resistant to high 

 temperatures and low salt or oxygen levels (McLease 1956) . 



Human Impacts 



Commercial harvesting is the principal limiting factor in adult populations of 

 lobsters. The fishing mortality rate of legal-sized lobsters in Maine may be 

 as high as 90% (Thomas 1977). In fact, results of a tagging study (Krouse 



12-16 



