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American lobster

American lobster
Temporal range: Pleistocene–Recent
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Family: Nephropidae
Genus: Homarus
Species: H. americanus
Binomial name
Homarus americanus
H. Milne-Edwards, 1837
Natural range of H. americanus (blue)
Synonyms [2]
  • Astacus marinus Say, 1817 (non Fabricius, 1775)
  • Astacus americanus Stebbing, 1893
  • Homarus mainensis Berrill, 1956

The American lobster, Homarus americanus, is a species of lobster found on the Atlantic coast of North America, chiefly from Labrador to New Jersey. It is also known as true lobster, northern lobster, or Maine lobster.[3][4] It can reach a body length of 64 cm (25 in), and a mass of over 20 kilograms (44 lb), making it the heaviest crustacean in the world. Its closest relative is the European lobster Homarus gammarus, which can be distinguished by its coloration and the lack of spines on the underside of the rostrum. American lobsters are usually bluish green to brown with red spines, but a number of color variations have been observed.


  • Distribution 1
  • Description 2
    • Head 2.1
    • Thorax 2.2
    • Coloration 2.3
  • Life cycle 3
  • Ecology 4
    • Diet 4.1
    • Diseases 4.2
      • Bacterial 4.2.1
      • Parasitic 4.2.2
      • Environmental 4.2.3
  • Taxonomy 5
  • As food 6
    • North American lobster industry 6.1
      • Canada 6.1.1
    • Management 6.2
  • References 7
  • Further reading 8
  • External links 9


Homarus americanus is distributed along the Atlantic coast of North America, from Labrador in the north to Cape Hatteras, North Carolina in the south.[5] South of New Jersey, the species is uncommon, and landings in Delaware, Maryland, Virginia and North Carolina usually make up less than 0.1% of all landings.[6] A fossil claw assigned to Homarus americanus was found at Nantucket, dating from the Pleistocene.[7][8] In 2013, An American Lobster was caught at the Farallon Islands off the coast of California.[9]


Profile of the anterior part of an American lobster

Homarus americanus commonly reaches 8–24 inches (200–610 mm) long and weighs 1–9 pounds (0.45–4.08 kg) in weight, but has been known to weigh as much as 44 lb (20 kg), making this the heaviest crustacean in the world.[10] Together with Sagmariasus verreauxi, it is also the longest decapod crustacean in the world;[2] an average adult is about 9 in (230 mm) long and weighs 1.5 to 2 lb (680 to 910 g). The longest American lobsters have a body (excluding claws) 64 cm (25 in) long.[2] According to Guinness World Records, the heaviest crustacean ever recorded was an American lobster caught off Nova Scotia, Canada, weighing 44.4 lb (20.1 kg).[10][11]

The closest relative of H. americanus is the European lobster, Homarus gammarus. The two species are very similar, and can be crossed artificially, although hybrids are unlikely to occur in the wild since their ranges do not overlap.[12] The two species can be distinguished by a number of characteristics:[13]

  • The rostrum of H. americanus bears one or more spines on the underside, which are lacking in H. gammarus.
  • The spines on the claws of H. americanus are red or red-tipped, while those of H. gammarus are white or white-tipped.
  • The underside of the claw of H. americanus is orange or red, while that of H. gammarus is creamy white or very pale red.


The antennae measure about 2 in (51 mm) long and split into Y-shaped structures with pointed tips. Each tip exhibits a dense zone of hair tufts staggered in a zigzag arrangement. These hairs are covered with multiple nerve cells that can detect odors. Larger, thicker hairs found along the edges control the flow of water, containing odor molecules, to the inner sensory hairs.[14] The shorter antennules provide a further sense of smell. By having a pair of olfactory organs, a lobster can locate the direction a smell comes from, much the same way humans can hear the direction a sound comes from. In addition to sensing smells, the antennules can judge water speed to improve direction finding.

Lobsters have two urinary bladders, located on either side of the head. Lobsters use scents to communicate what and where they are, and those scents are in the urine. They project long plumes of urine 1–2 meters (3 ft 3 in–6 ft 7 in) in front of them, and do so when they detect a rival or a potential mate in the area.[15]


The first pair of pereiopods (legs) is armed with a large, asymmetrical pair of claws.[2] The larger one is the "crusher", and has rounded nodules used for crushing prey; the other is the "cutter", which has sharp inner edges, and is used for holding or tearing the prey.[13]


The normal coloration of Homarus americanus is "dark bluish green to greenish brown", redder on the body and claws, and greener on the legs.[5] This coloration is produced by mixing yellow, blue, and red pigments.[16] Despite the rarity of strangely colored lobsters, many more of them are reported being caught. It is unclear as to whether this is an artifact of social media (i.e. it is easier to report catching a strangely colored lobster), or if it is due to a drop in predator populations.[17]

Color variants

An estimated one in 2 million lobsters are blue.[18] A genetic mutation causes a blue lobster to produce an excessive amount of a particular protein.[19] The protein and a red carotenoid molecule known as astaxanthin combine to form a blue complex known as crustacyanin, giving the lobster its blue color.[20] In 2009 a blue lobster was caught in New Hampshire;[21] in 2011, two blue lobsters were caught in Canada, one off of Prince Edward Island,[22] and another in the Esgenoôpetitj First Nation territory in New Brunswick;[22] another was caught in May 2012 off Nova Scotia.[23] Most recently a blue lobster was caught off Pine Point in Scarborough, Maine in August 2014, and was donated to a local aquarium to join 3 other blue lobsters.[24]

Yellow lobsters are the result of a rare genetic mutation and the odds of finding one are estimated to be 1 in 30 million.[18][25] Reports of yellow lobsters include one off Whaleback Island (at the mouth of the Kennebec River), Maine, on August 1, 2006,[26] off Prince Edward Island, Canada, on June 11, 2009,[27] one discovered in Wainani Kai Seafoods in Kalihi, Hawaii in a shipment from Nova Scotia on April 30, 2010,[28] in Narragansett Bay off Rhode Island on July 31, 2010,[16] and one off the coast of Black Point in Niantic, Connecticut on June 9, 2014.[29]

In July 2010, an albino lobster was reportedly caught in Gloucester.[30] An estimated only one in 100 million lobsters is albino — lacking in colored pigments.[18][30]

On August 28, 2010, a calico lobster with a mottled orange and black shell was reported to have been caught in Maine.[31] Only albino lobsters are rarer, and orange lobsters such as these are a 1 in 30 million catch.[18][32]

Several lobsters have been caught with different colorings on their left and right halves.[33] For instance, on July 13, 2006, a Maine fisherman caught a brown and orange lobster, and submitted it to the local oceanarium,[34] which had only seen three lobsters of this kind in 35 years. The chance of finding one is estimated at 1 in 50 million.[18][27] Many split-colored lobsters observed have been hermaphroditic chimeras,[35] but not all.[36]

Red lobsters are the usual result of a lobster being cooked. There is a 1 in 10 million chance of catching one alive with that color.[18][37]

Life cycle

A female lobster carrying eggs on her pleopods. Note the tail flipper second from left which has been notched by researchers to indicate she is an active breeding female.

The life cycle of H. americanus is well understood.[38] Mating only takes place shortly after the female has molted, and her exoskeleton is still soft.[39] The female releases a pheromone which causes the males to become less aggressive and to begin courtship, which involves a courtship dance with claws closed.[39] Eventually, the male inserts spermatophores (sperm packets) into the female's seminal receptacle using his first pleopods; the female may store the sperm for up to 15 months.[39]

The female releases eggs through her oviducts, and they pass the seminal receptacle and are fertilized by the stored sperm.[39] They are then attached to the female's pleopods (swimmerets) using an adhesive, where they are cared for until they are ready to hatch.[39] The female cleans the eggs regularly, and fans them with water to keep them oxygenated.[40] The large telolecithal[38] eggs may resemble the segments of a raspberry,[39] and a female carrying eggs is said to be "in berry".[39] Since this period lasts 10–11 months, berried females can be found at any time of year.[2] In the waters off New England, the eggs are typically laid in July or August, and hatch the following May or June.[38] The developing embryo passes through several molts within the egg, before hatching as a metanauplius larva. When the eggs hatch, the female releases them by waving her tail in the water, setting batches of larvae free.[40]

The metanauplius of H. americanus is 13 in (8.5 mm) long, transparent, with large eyes and a long spine projecting from its head.[39] It quickly molts, and the next three stages are similar, but larger.[39] These molts take 10–20 days, during which the planktonic larvae are vulnerable to predation; only 1 in 1,000 is thought to survive to the juvenile stage.[39] To reach the fourth stage – the post-larva – the larva undergoes metamorphosis, and subsequently shows a much greater resemblance to the adult lobster,[38] is around 12 in (13 mm) long,[39] and swims with its pleopods.[38]

After the next molt, the lobster sinks to the ocean floor, and adopts a benthic lifestyle.[40] It molts more and more infrequently, from an initial rate of ten times per year to once every few years.[39] After one year, it is around 1–1.5 in (25–38 mm) long, and after six years, it may weigh 1 pound (0.45 kg).[39] By the time it reaches the minimum landing size, an individual may have molted 25–27 times, and thereafter each molt may signal a 40%–50% increase in weight, and a 14% increase in carapace length.[40]


The American lobster thrives in cold, shallow waters where there are many rocks and other places to hide from predators. It typically lives at a depth of 4–50 m (13–164 ft), but can be found up to 480 m (1,570 ft) below the surface.[2]


The natural diet of H. americanus is relatively consistent across different habitats. It is dominated by mollusks (especially mussels), echinoderms and polychaetes, although a wide range of other prey items may be eaten, including other crustaceans, brittle stars and cnidarians.[41] Lobsters in Maine have been shown to gain 35-55% of their calories from herring, which is used as bait from lobster traps.[42] Only 6% of lobsters entering lobster traps to feed are caught.



Gaffkemia or red-tail is an extremely virulent infectious disease of lobsters caused by the bacterium Aerococcus viridans.[43] It only requires a few bacterial cells to cause death of otherwise healthy lobsters. The "red tail" common name refers to a dark orange discoloration of the ventral abdomen of affected lobsters. This is, in fact, the hemolymph or blood seen through the thin ventral arthrodial membranes. The red discoloration comes from astaxanthin, a carotenoid pigment exported to the blood during times of stress. The same sign is also seen in other diseases of lobsters and appears to be a nonspecific stress response, possibly relating to the antioxidant and immunostimulatory properties of the astaxanthin molecule.

Epizootic shell disease is a bacterial infection which causes black lesions on the lobsters' dorsal carapaces, reducing their saleability and sometimes killing the lobsters.[44]

Limp lobster disease caused by systemic infection by the bacterium Vibrio fluvialis (or similar species) causes lobsters become lethargic and die.[43][45]


amebic gill disease in farmed Atlantic salmon, Salmo salar. Infection occurs throughout the tissues, causing granuloma-like lesions, especially within the ventral nerve cord, the interstices of the hepatopancreas and the antennal gland. Paramoebiasis is strongly suspected to play a prominent role in the rapid die-off of American lobsters in Long Island Sound that occurred in the summer of 1999.[43]


Excretory calcinosis in American lobsters in Long Island Sound was described in 2002. The disease causes mineralized calculi to form in the antennal glands and gills. These cause a loss of surface area around the gills, and the lobster eventually asphyxiates. Several reasons have been proposed for the cause of a recent outbreak of the disease. The most generally attributed factor is an increased duration of warmer temperatures in the bottom of the Long Island Sound.[46][47]


The American lobster was [2]

As food

Global capture production in tonnes by year
A cooked lobster

American lobsters are a popular food.[48] They are commonly boiled or steamed. Hardshells (lobsters that are several months past their last molt) can survive out of water for up to two days if kept refrigerated. Softshells (lobsters that have only recently molted) do not survive more than a few hours out of water. Lobsters are usually cooked alive,[49] which may be illegal in certain areas [50] and which some people consider inhumane.[51][52]

One common way of serving lobster 'tail' (actually the tomalley that performs the functions of the liver and pancreas in a human, i.e., it filters out toxins from the body.[54] Some diners consider it a delicacy, but others avoid it because they consider it a toxin source or dislike eating innards.

A set of nutcrackers and a long, thin tool for pulling meat from inaccessible areas are suggested as basics, although more experienced diners can eat the animal with their bare hands or a simple tool (a fork, knife or rock). Eating a lobster can get messy, and most restaurants offer a lobster bib.[55] Meat is generally contained in the larger claws and tails, and stays warm quite a while after being served. There is some meat in the legs and in the arms that connect the large claws to the body. There is also some small amount of meat just below the carapace around the thorax and in the smaller legs.

North American lobster industry

Most lobsters come from the northeastern coast of North America, with the Atlantic Provinces of Canada and the U.S. state of Maine being the largest producers. They are caught primarily using lobster traps, although lobsters are also harvested as bycatch by bottom trawlers, fishermen using gillnets, and by scuba divers in some areas. Maine completely prohibits scuba divers from catching lobsters (violations could result in up to a $1000 fine). Maine also strictly prohibits the landing of lobsters caught by bottom trawlers and other "mobile gear".[56] Massachusetts offers scuba divers lobster licenses for a fee, and they are only available to state residents. Rhode Island also requires divers to acquire a permit.

Lobster traps are rectangular cages made of vinyl-coated galvanized steel mesh or wood, with woven mesh entrances. These are baited and lowered to the sea floor. They allow a lobster to enter, but make it difficult for the larger specimens to turn around and exit. This allows the creatures to be captured alive. The traps, sometimes referred to as "pots", have a buoy floating on the surface, and lobstermen check their traps between one and seven days after setting them. The inefficiency of the trapping system has inadvertently prevented the lobster population from being overfished. Lobsters can easily escape the trap, and will defend the trap against other lobsters because it is a source of food. An estimated 10% of lobsters that encounter a trap enter, and of those that enter only 6% will actually be caught.[57]

In the United States, the lobster industry is regulated. Every lobsterman is required to use a lobster gauge to measure the distance from the lobster's eye socket to the end of its carapace: if the lobster is less than 3.25 inches (83 mm) long, it is too young to be sold and must be released back to the sea. There is also a legal maximum size of 5 in (130 mm) in Maine, meant to ensure the survival of a healthy breeding stock of adult males, but in parts of some states, such as Massachusetts, there is none. Also, traps must contain an escape hole or "vent", which allows juvenile lobsters and bycatch species to escape. The law in Maine and other states dictates a second large escape hole or "ghost panel" must be installed. This hole is held shut through use of biodegradable clips made of ferrous metal. Should the trap become lost, the trap eventually opens, allowing the catch to escape.[58]

To protect known breeding females, lobsters caught carrying eggs are to be notched on a tail flipper (second from the right, if the lobster is right-side up and the tail is fully extended). Following this, the female cannot be kept or sold, and is commonly referred to as a "punch-tail" or as "v-notched". This notch remains for two molts of the lobster exoskeleton, providing harvest protection and continued breeding availability for up to five years.[59]


Fishing boats in Yarmouth, Nova Scotia

In the late 1990s and early 21st century, lobster fishing was the cause of troubles between Acadians and Mi'kmaq First Nations in the Canadian Maritimes. The Acadian economy (and identity) relied substantially on fisheries, especially lobster. In 1998, the Supreme Court of Canada ruled in favor of the First Nations and granted them unlimited rights to natural resources, based on an 18th-century treaty. The federal government tried to take licenses and quotas from the traditional fishermen, whose fishing quota had already dropped dramatically in the years before, and give them to the natives. Burnt Church, a reserve between Miramichi and the Acadian town of Neguac, was the hub of these troubles. The tension increased and decreased with each fishing season, reaching its climax in April 2003, when a riot broke in the port of Shippagan, where three native-owned fishing ships and a fish processing plant were burnt down. Since then, efforts have been made to bring Acadians and natives closer together, and the tension has slowly abated.[60]


American lobster tends to have a stable stock in northern (colder) waters, but gradually decreases in abundance moving southward. To manage lobster populations, more regulations and restrictions, geared towards achieving sustainable populations, are implemented gradually southward.[61]


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Further reading

  • Francis Hobart Herrick (1911). Natural History of the American Lobster. Fishery Bulletin 747. Government Printing Office. 
  • Jan Robert Factor, ed. (1995). Biology of the Lobster: Homarus americanus. Academic Press.  

External links

  • "American lobster". NOAA FishWatch. 
  • The Lobster Institute at the University of Maine
  • UNH Lobster Research: Monitoring The Offshore Lobster Fishery (
  • Rhode Island Sea Grant Fact Sheet
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