(DRAFT) - Taxonomy
Species lobster, American
Species Id M070106
Date 26 AUG 96
TAXONOMY
NAME - lobster, American
OTHER COMMON NAMES - American lobste r, lobster, Maine lobster, northern lobster, blueshells, hard shell lobster, old shell lobster, blackshell, crack backer, shedder, soft shell, new shell, shadow, rubber shell, paper shell and buckle shell
ELEMENT CODE -
CATEGORY - Aquatic Crustaceans
PHYLUM AND SUBPHYLUM - ,
CLASS AND SUBCLASS - Crustacea,
ORDER AND SUBORDER - Decapoda,
FAMILY AND SUBFAMILY - Nephropidae,
GENUS AND SUBGENUS - Homarus,
SPECIES AND SSP - americanus,
SCIENTIFIC NAME - Homarus americanus
AUTHORITY - Herrick, 1895
TAXONOMY REFERENCES - 31
COMMENTS ON TAXONOMY -
Common names include American lobster, lobster, Maine lobster, northern
lobster, blueshells (color variant), hard shell lobster, old shell lobster;
blackshell, crack backer (lobsters preparing to molt); shedder, soft shell,
new shell, shadow, rubber shell, paper shell, and buckle shell (recently
molted lobsters).*31* Taxonomists place lobsters in the phylum Arthropoda,
along with shrimp, crabs, barnacles, and insects. The arthropods (from the
Latin work arthro, meaning jointed, and the Greek poda, foot) are a group of
invertebrates with jointed appendages and a hard outer shell (exoskeleton).
Lobsters, crabs, and shrimp constitute the order Decapoda (Greek deca, ten).
As the name implies, all decapods have five pairs of legs. Lobsters and
shrimp have similar body structures, possessing large muscular tails that
they use to propel themselves backwards through the water away from danger.
Crabs, in contrast, have a very small tail that they keep tucked under their
bodies.
There are two commercially important families of edible lobsters. The
Nephropidae, which include the American lobster Homarus americanus, have one
pair of large claws and are found in the northern Atlantic Ocean. THe
Palinuridae, or spiny lobsters (also called rock lobsters), lack the large
claws and have spines all over their bodies. They live in subtropical and
tropical oceans.*278*
Taxonomy - 1 (DRAFT) - Status
Species lobster, American
Species Id M070106
Date 26 AUG 96
STATUS
Coded Status
Existing, FMP exists
Commercial
Commercial/consumption
REFERENCES FOR STATUS - 31
COMMENTS ON STATUS -
American lobsters support an important commercial fishery along the
northeastern coast of the U.S. They are abundant in coastal and offshore
waters. It is important that the impact of development projects on lobster
populations be considered so that this important and valuable natural
resource will be protected.*31*
Status - 1 (DRAFT) - Distribution
Species lobster, American
Species Id M070106
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine
Marine
Marine, subtidal
Marine, subtidal RB.
Marine, subtidal UB3
Marine, subtidal AB.
Marine, subtidal UB2
REFERENCES FOR NWI - 31 and 168
COMMENTS ON HABITAT ASSOCIATIONS -
The American lobster lives on subtidal bottoms. Lobsters are found
principally in the marine system and high salinity areas (>20 ppt) of the
estuarine system. 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.
Lobsters are found from mean low water level to depths over 2300 feet (700
m). Immediately after hatching, larvae assume a planktonic (suspended in
the water column) existence in Maine waters that lasts from 5 to 6 weeks.
On assuming a benthic existence, lobsters are considered juveniles.*168*
Substrate: Juvenile and adult American lobsters occupy substrates
characterized by sand-rock, bedrock-rock, mud-rock, mud-silt, and
clay-silt. The most common substrate occupied by inshore lobsters is sand
with overlying boulders. This substrate is uncommon in offshore areas where
it is usually restricted to the heads of submarine canyons. The most common
substrates in offshore areas are mud or clay with overlying silt. Lobsters
burrow or excavate bowlshaped depressions into these soft substrates for
cover and protection.*31*
ANIMAL/PLANT SPECIES ASSOCIATIONS -
Predators include: codfish, dogfish, catfish, and skate.*278*
REFERENCES FOR SPECIES ASSOCIATIONS - 278
Habitat Associations - 1 (DRAFT) - Food Habits
Species lobster, American
Species Id M070106
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
OMNIVORE
REFERENCES FOR TROPHIC LEVEL - 31
LIFESTAGE FOOD FOOD PART
General Plants Not Specified
General Hydrozoans Not Applicable
General Polychaetes Not Specified
General Echinoderms Not Specified
General Starfish Not Specified
General Sea/Heart Urchins Not Specified
General Molluscs Not Specified
General Crustaceans Not Specified
REFERENCES FOR GENERAL FOOD - 31 and 168
COMMENTS ON FOOD -
The diet of lobster is flexible and includes crustaceans (e.g., crabs),
molluscs (e.g., small clams), echinoderms, algae, and hydroids.*168*
Juvenile and adult lobsters are omnivorous. They are primarily predators,
catching live prey, but they also scavenge for food. The bulk of their diet
consists of bottom invertebrates, crabs, sea urchins, mussels, polychaetes,
periwinkles, and sea stars. Fish and plants also contribute to the diet.
American lobsters apparently prefer to eat crabs.
Sea urchins and sea stars contribute a much larger proportion of the diet
during the molting season than at other times of the year. This change in
diet during molting may be one of selectivity for prey high in calcium, an
important element in hardening the exoskeleton.
The diets of female and male lobsters are similar. Feeding activity
declines in the fall as water temperatures decrease, and remains low in
winter.*31*
The lobster feeds primarily at night and finds shelter in burrows or
crevices during the day.*168*
COMMENTS ON LARVAE FOOD -
American lobster larvae have been cultured on copepods and small lobster
larvae but little is known about their feeding habits in nature. Larvae
were raised on a diet of the copepods, Acartia, Tortanus, Eurytemora, and
Pseudocalanus, and grew well on a diet of smaller lobster larvae. Two
larvae collected in Massachusetts contained parts of crustacea, diatoms and
algae.*31*
Food Habits - 1 (DRAFT) - Environment Associations
Species lobster, American
Species Id M070106
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
E Water Temperature: Between 15-21 degrees C
E Water Temperature: Below 15 degrees C
E Water Temperature: Specified in Comments
L Water Temperature: Between 21-27 degrees C
L Water Temperature: Between 15-21 degrees C
L Water Temperature: Below 15 degrees C
L Water Temperature: Specified in Comments
A Water Temperature: Between 21-27 degrees C
A Water Temperature: Between 15-21 degrees C
A Water Temperature: Below 15 degrees C
A Water Temperature: Specified in Comments
L
L
J
J
J
J
A
A
A
A
A
G Water Depth Preference: Specified in Comments
J Substrate: Mud or silt
J Substrate: Sand
J Substrate: Rocks
J Substrate: Plants
J Relation to Substrate: Occurs in substrate [penetrating]
J Relation to Substrate: Unattached - normally free living
A Substrate: Mud or silt
A Substrate: Sand
A Substrate: Rocks
A Substrate: Plants
A Relation to Substrate: Occurs in substrate [penetrating]
A Relation to Substrate: Unattached - normally free living
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 31 and 168
REFERENCES FOR FEEDING ADULT ENVIRONMENTAL ASSOC_ - 31
Environment Associations - 1 (DRAFT) - Environment Associations
Species lobster, American
Species Id M070106
Date 26 AUG 96
REFERENCES FOR FEEDING JUVENILE ENVIRONMENTAL ASSOC_ - 31
REFERENCES FOR FEEDING LARVAE ENVIRONMENTAL ASSOC_ - 31
REFERENCES FOR EGG ENVIRONMENTAL ASSOC_ - 31
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Temperature, salinity, and substrate are the most critical factors
influencing lobster distribution and abundance. Also there is some
evidence that lobster activity and feeding may be light dependent.*31*
Temperature:
Changes in water temperature stimulate migration of offshore lobsters which
tend to seek bottom water temperatures from 8 to 14 degrees C. During the
spring, lobsters offshore move from the outer Continental Shelf and upper
slope to shallower water along the southern New England Continental Shelf,
including Georges Bank and the coastal waters of New York,Rhode Island, and
southern Massachusetts. It is possible that bottom water temperatures (8 to
14 degrees C) in the shallower waters are more suitable for the extrusion of
eggs, molting and mating than are the summer bottom temperatures over the
outer Continental Shelf and upper slope. Return lobster migrations to the
outer shelf and upper slope waters begin in late summer and continue through
November as inshore bottom water temperatures drop. By December the
lobsters offshore have returned to the outer shelf and upper slope waters
where bottom temperatures are 8 to 12 degrees C.*31*
Dissolved Oxygen:
American lobsters can survive relatively low dissolved oxygen
concentrations. Acclimation levels of temperature and salinity
significantly affect the lower lethal oxygen concentration whereas
acclimation level of oxygen does not have a significant effect.*31*
Salinity:
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. Under natural conditions, lobsters,
particularly larvae, probably avoid areas where the salinity is lower than
approximately 20 ppt.*168*
COMMENTS ON FEEDING ADULT ENVIRONTAL ASSOC_ -
Temperature:
Juvenile and adult American lobsters tolerate sea water temperatures
ranging from -1 to 30.5 degrees C. Molting and growth cease when water
temperatures drop below 5 degrees C. Acclimation conditions significantly
affect the upper lethal temperature.*31*
Salinity:
For juvenile and adult lobsters acclimated to 27 combinations of salinity,
dissolved oxygen, and water temperature lower lethal salinities ranged from
6 ppt for lobsters acclimated at 5 degrees C, 6.4 mg/l oxygen, and 30 ppt
salinity to 16.4 ppt for lobsters acclimated at 25 degrees C, 6.4 mg/l
oxygen, and 30 ppt salinity. Due to osmoregulatory stress, molting
lobsters are less resistant to low salinities than hard-shelled
Environment Associations - 2 (DRAFT) - Environment Associations
Species lobster, American
Species Id M070106
Date 26 AUG 96
lobsters.*31*
Substrate:
Juvenile and adult American lobsters occupy substrates characterized by
sand-rock, bedrock-rock, mud-rock, mud-silt, and clay-silt. The most
common substrate occupied by inshore lobsters is sand with overlying
boulders. This substrate is uncommon in offshore areas where it is usually
restricted to the heads of submarine canyons. The most common substrates
in offshore areas are mud or clay with overlying silt. Lobsters burrow or
excavate bowlshaped depressions into these soft substrates for cover and
protection.*31*
COMMENTS ON FEEDING JUVENILE ENVIRONMENTAL ASSOC_ -
Temperature:
Juvenile and adult American lobsters tolerate sea water temperatures
ranging from -1 to 30.5 degrees C. Molting and growth cease when water
temperatures drop below 5 degrees C. The upper lethal temperatures (LD50
in 48 h) of lobsters acclimated to 27 combinations of temperature (5, 10,
15 degrees C), salinity (20, 25, 30 ppt), and dissolved oxygen (2.9, 4.3,
6.9 mg/l) have been reported. Acclimation conditions significantly
affected the upper lethal temperature.*31*
Salinity:
For juvenile and adult lobsters acclimated to 27 combinations of salinity,
dissoved oxygen, and water temperature lower lethal salinities ranged from
6 ppt for lobsters acclimated at 5 degrees C, 6.4 mg/l oxygen, and 30 ppt
salinity to 16.4 ppt for lobsters acclimated at 25 degrees C, 6.4 mg/l
oxygen, and 30 ppt salinity. Due to osmoregulatory stress, molting
lobsters are less resistant to low salinities than hard-shelled
lobsters.*31*
Substrate:
Juvenile and adult American lobsters occupy substrates characterized by
sand-rock, bedrock-rock, mud-rock, mud-silt, and clay-silt. The most
common substrate occupied by inshore lobsters is sand with overlying
boulders. This substrate is uncommon in offshore areas where it is usually
restricted to the heads of submarine canyons. The most common substrates
in offshore areas are mud or clay with overlying silt. Lobsters burrow or
excavate bowlshaped depressions into these soft substrates for cover and
protection.*31*
COMMENTS ON FEEDING LARVAE ENVIRONMENTAL ASSOC_ -
Temperature:
The average surface water temperatures during peak larval densities in
Boothbay Harbor, Maine, range from 13.7 to 15.0 degrees C. These water
temperatures are the maximum for the region. Larval densities in Buzzards
Bay, Massachusetts, peaked when the surface water temperature was about 19
degrees C and the bottom water temperature was about 17 degrees C. Surface
water temperatures ranged from 10.3 to 25.5 degrees C when larvae were
collected in Massachusetts.*31*
The development of larvae is temperature dependent. Lobster larvae are
less tolerant to low temperatures than juveniles or adults. In one
experiment all larvae died prior to molting at 5 degrees C.*31*
Environment Associations - 3 (DRAFT) - Environment Associations
Species lobster, American
Species Id M070106
Date 26 AUG 96
Salinity:
Studies of American lobster larvae exposed to various salinities in water
temperatures of 15.0 to 17.5 degrees C, revealed that survivial was highest
at a salinity of 30 ppt and salinities a low as 21 ppt were only slightly
less suitable. Survival of larvae to stage IV decreased as salinities
dropped below 21 ppt, and no larvae survived less than 17.0 ppt. Larvae
attempted to avoid salinities as low as 21.4 ppt at water temperatures near
22 degrees C. There is no information on survival rates of lobsters at
unusually high salinities.*31*
COMMENTS ON EGG ENVIRONMENTAL ASSOC_ -
Eggs of American lobsters hatch at water temperatures as low as 8 degrees C
in northern New England. Hatching usually begins when water temperatures
are about 15 degrees C and peaks near 20 degrees C.*31*
Environment Associations - 4 (DRAFT) - Life History
Species lobster, American
Species Id M070106
Date 26 AUG 96
LIFE HISTORY
Morphology/Identification Aids
The American lobster has five cephalic and eight thoracic segments fused
together to form a cephalothorax, which is covered by a shield-like
carapace. All the segments comprising the cephalothorax bear appendages.
Beginning anteriorly, the appendages of the cephalothorax are the first
antennae, second antennae, mandibles, first maxillae, second maxillae,
first, second, and third maxillipeds and five pairs of walking legs, or
pereiopods. The first three pairs of pereiopods are chelate, the first pair
modified into large claws. One claw of this pair, the crusher, is larger
than the other claw, the cutter. American lobsters have compound eyes that
are movable and stalked.
The six body segments posterior of the carapace make up the abdomen.
Paired, biramous pleopods are located on the first five abdominal segments.
The last abdominal segment consists of the telson flanked by uropods, which
are modified pleopods. The broad tail fin, composed of the telson and
uropods, is used for backward swimming, which is characteristic of lobsters.
The first pair of pleopods on male lobsters are modified into rigid
structures, gonapods, which are used to convey sperm to the female. In
females, the first pair of pleopods are similar to the others but are much
smaller. There are two characteristics used to separate the sexes of mature
lobsters. Males have sharp spines under the abdomen; female spines are
blunt. The male's abdomen is narrower than the width of the carapace;
those in the female are about equal.
American lobsters are normally greenish-brown but some specimens are blue,
red, reddish-yellow, cream, black, or calico. Diet, heredity, and exposure
to light all affect a lobster's color. The major pigment in a lobster's
shell, astaxanthin, is actually bright red in its free state; but in the
lobster's shell astaxanthin is chemically bonded to proteins that change it
to a greenish or bluish color. When lobsters are cooked, heat breaks down
these bonds, freeing the astaxanthin so that it reverts to its normal red
color.*278*
The largest American lobsters are males. The largest male on record
weighed 19.25 kg, and was 63.4 cm long. The heaviest female weighted 8.35
kg.
The total propodite length in relation to carapace length is a means of
distinguishing between the larval stages of the American lobster and the
European lobster, Homarus gammarus. The total propodite length is greater
than the carapace length of the European lobster larvae. The opposite is
true for American lobster larvae. Geographic isolation is the only
character that distinguishes the adults of the two species.*31* A lobster's
hard outer shell does not grow. Homarus can only increase its size by
molting periodically. In preparation for molting, the lobster lays down a
new, soft shell underneath its old shell. Just prior to shedding the old
shell, the lobster seeks out a protected shelter - a rocky cave or crevice -
because a newly-molted lobster is soft and helpless, unable to move. Then
the lobster rolls over on its side, bends into a V shape, shrinks its
extremities (especially the large claws) by drawing fluids from them, and
withdraws from its shell. Over a period of several hours after molting, the
lobster swells to a larger size and the new shell begins to harden.*278*
Autotomy - Lobsters are able to detach and discard legs or claws by a
Life History - 1 (DRAFT) - Life History
Species lobster, American
Species Id M070106
Date 26 AUG 96
process called autotomy. This "self-amputation" can help a lobster to
escape a predator's grasp. A lobster may also detach a claw if it is unable
to withdraw it from its old shell during molting. Autotomized limbs can be
regenerated. After the next molt they appear fully formed but smaller than
usual, and after several molts they are full-sized.
Spawning:
Male American lobsters mature at shorter lengths than females. Most males
carry viable spermatozoa when the carapace length (CL) (measured from tip of
rostrum to the back of the carapace) is 40 to 45 mm. Females in Maine
mature when they are about 90 mm CL but in warmer waters (Long Island
Sound), most mature at lengths of 70 to 74 mm CL.
Small males usually cannot mate successfully with larger females. Males may
be capable of producing mature spermatozoa when they are 40-45 mm CL but
they may not be capable of mating until they are as large as the smallest
mature females.
When spawning, lobsters pair for about 2 weeks. Females leave their
solitary shelters about 7 days before molting and share the shelter of a
dominant, territorial male.
A female sex pheromone is produced before or at the time of molting. This
pheromone suppresses male aggression and induces courtship. Pre-molt
behavioral displays are also important in successful pair formation. Mating
usually takes place 20-40 minutes after the female has molted. One female,
however, was reported to have successfully mated 12 days after molting.
Successful mating of hard shelled female lobsters several months after
molting has been reported.
Males larger than the female are most successful at copulation. Males
protect females from predation and cannibalism for up to 7 days during the
vulnerable post-molt stage. This "protection" by the male also ensures that
other males will not copulate with his mate.
Eggs are normally extruded 11 to 13 months after mating. As ova are
released, they are fertilized by part of the spermatozoa stored in the
seminal receptacle. Oviposition occurs on a two year cycle even if the
female is not carrying spermatozoa. Evidence is strong that eggs are
fertilized externally as they pass over the seminal receptacle, but some
believe that fertilization is internal.
Females are capable of fertilizing at least two successive batches of eggs
from a single mating. Large females do not molt or mate every year.*31*
Eggs and Fecundity:
Freshly extruded American lobster eggs are dark green and irregulary shaped.
They soon become spherical and telolecithal, and are about 1.5 to 1.7 mm in
diameter. As eggs develop, they increase in size and become elongated and
lighter in color.
The number of eggs in a clutch ranges from 3,000 to 115,000.
After extrusion, fertilized eggs become firmly attached to pleopods, where
they develop for 9-11 months. About 36% of the eggs are lost between
extrusion and hatching. Temperature is a key factor that determines the
length of time the eggs are carried on the pleopods. Eggs develop to the 16
cell stage in two days at 18.5 degrees C, and 4.8 days at 10.5 degrees C.
Lobster eggs hatch from May to October; the warmer the water the earlier
Life History - 2 (DRAFT) - Life History
Species lobster, American
Species Id M070106
Date 26 AUG 96
the hatch. In Massachusetts, eggs begin hatching in mid or late May when
water temperatures are about 15 degrees C. Peak hatching is in June and
early July when water temperatures reach 20 degrees C. The time required to
hatch all the eggs within a brood depends on the water temperature. All
eggs within a brood usually hatch in 2 to 3 days at 20 degrees C, and in
10-14 days at 15 degrees C.
Females release larvae during a brief period at night by actively beating
their pleopods. Females normally molt and mate within one month after their
brood has hatched.*31*
Prelarvae and Larvae:
American lobsters pass through one prelarval and four free-swimming larval
stages before settling to the bottom and molting into juveniles. Most
prelarvae molt into the first larval stage before being released by females.
All larval stages are normally completed in 25-35 days, but the length of
time is temperature dependent.
The distribution and abundance of larvae are affected by the distribution of
spawning females, surface current velocity and direction, temperature,
salinity, light intensity, hydrostatic pressure, and larval mortality. The
larvae are planktonic from late May to October; they appear earlier in the
plankton in southern New England than in the Gulf of Maine.
Vertical distribution is affected by light intensity. At night the larvae
seek deeper waters but return near the surface during day. Phototactic
responses observed in the laboratory differed among larval stages and
within each larval stage.
High larval densities along windward coasts suggest that larvae are
transported by surface currents. Prevailing south-westerly winds along the
New England coast in the summer may transport larvae from offshore to
coastal waters.
Late in stage IV, larvae settle to the bottom and burrow into the substrate.
They molt into juveniles while sheltered in their burrows.*31*
Juveniles and Adults:
American lobsters in inshore waters excavate shelters under objects resting
on the sea floor when there are no natural crevices available as shelter.
Highest lobster densities are on sand substrate with overlying flattened
rocks. Juvenile and adult lobsters are negatively phototactic and prefer
dark shelters shaped so that the lobster can maintain contact with the roof
and walls.
Lobsters inshore tend to be solitary. They rarely share shelters, and
sharing behavior has only been reported in winter when bottom water
temperatures are coldest. Lobsters offshore often share shelters or
bowl-shaped depressions in the substrate. This behavior may be caused by
the scarcity of shelters.
Juvenile American lobsters less than 35 mm CL rarely leave their shelters.
When juveniles are 35-40 mm CL they begin nocturnal foraging away from their
shelters. Adult and juvenile lobsters usually travel less than 300 m from
the home shelter when foraging.
Lobsters inshore move from shoal water (< 10 m) to deeper water when storms
generate heavy seas. These horizontal movements are usually 100 m or less
but involve an increase in depth up to 10 m. Lobsters along the Canadian
Life History - 3 (DRAFT) - Life History
Species lobster, American
Species Id M070106
Date 26 AUG 96
east coast make short distance seasonal movements from relatively deep
waters (15-18 m) in winter to shallower waters (7-9m) in summer.
Lobsters inshore appear to have a limited home range. Large lobsters
apparently migrate farther than small lobsters.
Lobsters offshore migrate greater distances than their coastal counterparts.
Molting and Growth Characteristics:
The growth of lobsters is continous, but it is greatest when they molt. The
growth rate depends on the molting frequency and the size increase at
molting. With increasing age, American lobsters molt less frequently and
grow proportionally less at each molt. Lobsters molt an average of 10 times
in their first year, 3 or 4 times in the second and third years, twice in
the fourth year, and once a year or less thereafter.
Although salinity, dissolved oxygen, food availability, and crowding are
factors that affect growth, temperature appears to be the dominant factor.
Mature females have a slower growth rate than males because females molt
less frequently. Growth between molts for the two sexes is similar.
Lobsters offshore grow faster per molt than lobsters inshore that are the
same size. Lobsters offshore molt more often than lobsters inshore. The
difference in growth rates of inshore and offshore lobsters may be explained
by the migratory habits of the two populations. Each year offshore lobsters
migrate between the outer Continental Shelf and upper slope waters (8 to 12
degrees C) and shallower Continental Shelf waters (10 to 17.5 degrees C)
seeking optimum water temperatures for growth, molting, and extrusion of
eggs, whereas inshore lobsters are nonmigratory and subject to winter
temperatures (<5 degrees C) that inhibit growth.*31*
Population Dynamics:
Natural mortality is extremely high during the free-swimming planktonic
larval stages of the American lobster. Annual exploitation rates of
lobsters near Comfort Cove, Newfoundland, were as high as 95%.
Lobster movements usually are triggered by changes in water temperature. A
strong correlation between catch, fishing effort, and sea surface
temperature has been reported.*31*
Mortality and Molting:
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.*168*
Predation:
Juvenile and adult American lobsters are comsumed by many bottom feeding
fishes. Atlantic cod stomachs often are filled with juvenile lobsters.
Most lobsters eaten by fish are less than 50 mm CL, but larger lobsters are
eaten by Atlantic cod, sharks, wolffish, pollock, and goosefish. Skates,
rays, cummer, tautog, striped bass, black sea bass, sea ravens, haddock,
Life History - 4 (DRAFT) - Life History
Species lobster, American
Species Id M070106
Date 26 AUG 96
tilefish, conger ells, and weakfish sometimes prey upon juvenile lobsters.
Predators of lobster larvae have not been identified but the planktonic
larvae probably are consumed by surface-feeding planktivorous fishes.*31*
Diseases and Parasites:
Few diseases are known at the present time which affect the American
lobster. Gaffkemia (Aerococcus viridans var. homari) and "shell" disease are
two bacterial diseases that cause high mortality in holding pens. Incidence
of gaffkemia in lobsters from natural populations along the Maine coast
averaged 7%. Lobsters also are infected with fungal diseases and epibiotic
growths. Mussels, barnacles, marine algae, filamentous bacteria, stalked
protozoams, and diatoms sometimes may completely cover the exoskeleton. A
trematode (Stichocotyle nephropsis), copepod (Unicaleuthes), Acanthocephela,
and protozoa (Porospora gigantea, Anophys sp.) are parasites of the
lobster.*31*
Migrations:
Changes in water temperature stimulate migrations of offshore lobsters which
tend to seek bottom water temperatures from 8 to 14 degrees C. During the
spring, lobsters offshore move from the outer Continental Shelf and upper
slope to shallower water along the southern New England Continental Shelf,
including Georges Bank and the coastal waters of New York, Rhode Island, and
southern Massachusetts. It is possible that bottom water temperatures (8 to
14 degrees C) in the shallower waters are more suitable for the extrusion of
eggs, molting and mating than are the summer bottom temperatures over the
outer Continental Shelf and upper slope. Return lobster migrations to the
outer shelf and upper slope waters begin in late summer and continue through
November as inshore bottom water temperatures drop. By December the
lobsters offshore have returned to the outer shelf and upper slope waters
where bottom temperatures are 8 to 12 degrees C.*31*
Behavior:
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.*168*
LIFE HISTORY CODES -
Foraging Strategy: Scavenging
Duration of Pair Bond: Pair for one breeding season
Average Number of Offspring/Reproductive Effort: Grea
Periodicity: Active at night
COMMENTS ON LIFE HISTORY -
Lobsters crawl rather than swim. In Homarus, the first of the five pairs of
walking legs is modified to form the larger crusher and ripper claws.
Underneath the abdomen (stomach) of Homarus are six pairs of swimmerets
(pleopods); the last pair is enlarged to form the tail fan. The shieldlike
shell covering the main portion of the lobster's body called the carapace.
Lobsters have compound eyes that are carried on movable eye stalks. Each
Life History - 5 (DRAFT) - Life History
Species lobster, American
Species Id M070106
Date 26 AUG 96
eye is made up of approximately 14,000 individual units. Lobsters can
detect movement, and they may be able to perceive images. It is not known
whether lobsters can distinguish colors as can other decapods.
REFERENCES FOR LIFE HISTORY- 31 and 168
Life History - 6 (DRAFT) - Management Practices
Species lobster, American
Species Id M070106
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Existing Regulating harvest of species being described
Existing Regulating harvest - setting seasons
Existing Regulating harvest - restricting sex to be hunted
Existing Regulating harvest - setting size limits
Existing Regulating commercial harvest gear types
Existing Regulating commercial harvest levels
Beneficial Controlling pollution [thermal, chemical, physical]
Adverse Other management practices [specified in comments]
REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 168
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 168
REFERENCES FOR EXISTING MANAGEMENT PRACTICES - 31 and 168
COMMENTS ON MANAGEMENT PRACTICES -
It is important that the impact of development projects on lobster
populations be considered so that this important and valuable natural
resource will be protected.*31*
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%. Recently molted animals actively seek food and may
be trapped by fishermen more easily than hard-shelled lobsters which
may confine their feeding activity to a smaller territory.*168*
Pertubations such as oil spills, dredging, spoil disposal, and discharge of
contaminants could potentially affect lobster populations.*168*
Management:
Maine produces the greatest number of lobsters. In that state,
many types of restrictive regulations apply to the lobster fishery. They
include: licensing; use of conventional traps with escape vents; maximum
and minimum-size restrictions; prohibition of removing berried lobsters,
scrubbing eggs off, or removing those marked with a notch (marked to
identify egg carrying females) on the second flipper from the right; trap
limitations on a single line in some areas; and limitation of fishing hours
in the summer.*168*
The states of New Hampshire and Massachusetts also have regulations limiting
the harvest of lobsters. The New England Regional Fisheries Management
Council has a management plan for the offshore (3-200 miles) lobster
fishery which was to take effect in 1985.*31*
Aquaculture:
Attempts have been made to explore the potential of the American lobster for
aquaculture. If lobsters could be raised successfully it might be possible
to supplement natural populations as well as support commercial
Management Practices - 1 (DRAFT) - Management Practices
Species lobster, American
Species Id M070106
Date 26 AUG 96
aquaculture. Although this species has been raised to adulthood in the
laboratory, large-scale aquaculture is impractical. The aggressiveness of
the species requires that each lobster be raised in an individual container,
feeding is expensive,and lobsters are more susceptible to disease in culture
than in the natural environment.*168*
Gear:
Traditionally, lobsters are caught in baited traps (pots). Most lobsters
are caught in shallow (5-30m) inshore waters.*31*
Management Practices - 2 (DRAFT) - References
Species lobster, American
Species Id M070106
Date 26 AUG 96
References
31* MacKenzie, C., J. Moring. 1985. Species Profiles: Life Histories
and Environmental Requirements of Coastal Fishes and
Invertebrates (North Atlantic) -- American Lobster. U.S. Fish
and Wildlife Service Biol. Rep. 82(11.33) pp 19.
168* Fefer, Stewart, Patricia Schettig. 1980. An Ecological
Characterization of Coastal Maine. 1-3. Department of the
Interior.
References - 1