Megalops atlanticus

Geographic Range

Megalops atlanticus , commonly known as the Atlantic tarpon, is primarily found in the warm, shallow, coastal regions of the eastern and western Atlantic Ocean. These fish have a wide range along the coastal areas from the United States to Brazil in the western Atlantic and from Senegal to the Congo on the eastern Atlantic coast. They have occasionally been sighted as far north as Nova Scotia and as far south as Argentina in the western Atlantic and along the coasts of Portugal, the Azores and the south of France in the eastern Atlantic. Megalops atlanticus is also found throughout the Caribbean, Gulf of Mexico, around Bermuda and in the eastern Pacific Ocean near Cobia Island in Panama because of movement through the Panama Canal.

• Biogeographic Regions
• nearctic nearctic
  • native native
• ethiopian ethiopian
  • native native
• neotropical neotropical
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • introduced introduced
• mediterranean sea
  • native native

Habitat

Tarpon are found in estuaries, bays, lagoons and have even been known to travel up into freshwater rivers. Megalops atlanticus has the ability to tolerate euryhaline environments and can also tolerate environments which are oxygen poor by gulping air at the surface. The only environmental constraint on their habitat is temperature. They occupy warmer waters in subtropical areas and sudden temperature changes have been known to kill tarpon in large numbers. M. atlanticus is a pelagic fish.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• pelagic pelagic
• rivers and streams
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• riparian riparian
• estuarine estuarine

Physical Description

Megalops atlanticus is a large fish with a deep blue to black dorsal coloration and silver side and ventral coloration. Tarpon have a forked, homocercal caudal fin. The single dorsal fin is short and made up of 13 to 15 soft rays; the last of these rays is elongated into a heavy filament. The anal fin is a triangle and is made up of 22 to 25 soft rays; the last of these rays is also elongated into a filament but is much smaller than that of the dorsal fin. Tarpon have large pelvic fins on the abdomen and long pectoral fins made up of 13 to 15 soft rays. The scales of tarpon are cycloid and large. There are 37 to 42 of these large scales along the lateral line.

Tarpon vary greatly in size and females are generally larger than males. Megalops atlanticus can grow up to lengths of 240 cm and reach a mass of 161 kg. Females, on average, have a mean fork length of 167.7 cm whereas males have a mean fork length of 144.7 cm.

The lower jaw of M. atlanticus is large and protruding. Tarpon have very small, densely packed teeth placed all over the mouth including the jaws, tongue and skull base. In addition to these fine teeth, tarpon have a bony plate on the upturned portion of the lower jaw which helps them crush some of their prey.

Tarpon have a modified swim bladder which allows them to live in oxygen-poor environments. Alveolar tissue in the swim bladder and a duct connecting the swim bladder to the esophagus allow tarpon to breath atmospheric air. Studies have shown that tarpon are obligate air breathers. Even in oxygen-rich environments tarpon still gulp air from the surface.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Megalops atlanticus develops in three distinct stages over a period of months. Two to three days after spawning, the eggs hatch into planktonic leptocephalus larvae. Over a period of two to three months these leptochephalus larvae grow to a length of 6 to 25 mm and float inshore on currents to continue their development. In stage two, tarpon actually stop growing and shrink to a size of approximately 14 mm. This stage lasts anywhere from 20 to 25 days. In stage three, lasting seven to eight weeks, the tarpons continue their growth and at around 40 mm become juveniles.

The sexual maturation of M. atlanticus is based primarily on the length of the fish. In males it occurs between 90 to 117.5 cm and in females at approximately 128.5 cm. This maturation can occur between the ages of 6 to 13 years for both sexes.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Tarpon spawn seasonally and are multiple spawners. These fish have been seen swimming in a circular, rotating fashion. This movement may be a way for tarpon to initiate spawning. Large schools of Megalops atlanticus , 25 to 200 individuals, migrate offshore to spawn. Tarpon are broadcast spawners. Fertilization of the eggs is external.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Large schools of Megalops atlanticus , 25 to 200 individuals, migrate offshore between May and August to spawn. There is some evidence to suggest that tarpon can spawn year round, but this is not common. There is also evidence to suggest that the lunar phase influences when tarpon spawn. Successful hatchings occur within the week following a new moon. These fish have a very high fecundity rate, with large females producing more than 12 million eggs. Tarpon spawn in the deeper waters and allow the currents to carry their eggs to inshore nurseries to develop. The eggs hatch into leptocephalus larvae after two or three days.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• broadcast (group) spawning
• oviparous oviparous

Tarpon expend energy travelling to their breeding grounds and producing their eggs and sperm, but they make no further investment in their offspring.

• Parental Investment
• no parental involvement

Lifespan/Longevity

Megalops atlanticus is known to have a very long lifespan. Tarpon are expected to live approximately 55 years in the wild and approximately 60 years in captivity. The oldest recorded age the wild was 55 years for a female and 43 years for a male. In captivity, the oldest recorded was a female tarpon which reached the age of 63 years.

Behavior

Megalops atlanticus forms small schools which become larger during spawning. Tarpon migrate offshore to spawn in the summer months and are also known to make more migrations throughout the year. Little is known about the extent or frequency of their travels. Tarpon tagged in Florida have been recaptured as far west as Louisiana and as far north as South Carolina.

• Key Behaviors
• natatorial natatorial
• motile motile
• migratory migratory
• social social

Home Range

Information on the home range of tarpon is unavailable.

Communication and Perception

The word " Megalops " translates from the Greek language as "large-eyed". The eyes of Megalops atlanticus are a very prominent feature and aid tarpon in hunting for prey. Tarpon have been known to make thumping noises to communicate with those around them or to scare off predators when they become startled. These noises are produced by vibrations in the swim bladder.

• Communication Channels
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical

Food Habits

The diet of Megalops atlanticus changes throughout development. In the first stage of their development, tarpon get nutrients directly from the water. As juveniles, they feed on zooplankton, small fish , and insects . As adults, tarpon move away from zooplankton and feed only on fish and crustaceans . Some main food sources are Atlantic needlefish ( Strongylura marina ), pinfish ( Lagodon rhomboides ), and many species of crabs and shrimp . Megalops atlanticus swallows its prey whole because of the small size of its teeth. Tarpon feed mostly on mid-water prey during the day and night.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods

• Animal Foods
• fish
• insects
• aquatic crustaceans
• zooplankton zooplankton

Predation

Zooplankton and small fish feed on M. atlanticus during the larval stage. As tarpon mature, their main predators become bull sharks ( Carcharhinus leucas ), great hammerhead sharks ( Sphyrna mokarran ), American alligators ( Alligator mississippiensis ) and many species of porpoise .

Tarpon exhibit a color pattern called countershading, which most fish use as a method to prevent predation. Their dorsal surface is generally a dark color. When a predator is looking down on a tarpon from above, the dark color of its dorsal side helps it blend in with the dark, deep waters. The ventral surface of most fish is lighter in color, silver in the case of the tarpon. This countershading helps it blend in with the lighter color of the surface water when a predator is looking at it from below.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Tarpon are prey and are also predators throughout their ecosystem. Large sharks , alligators and porpoises feed on tarpon and in return tarpon feed on smaller fish , crabs and shrimp .

Lecithochirium microstomum , a trematode parasite, is found in the stomachs of tarpon, and Bivescula tarponis , another trematode parasite, occurs throughout the intestines. The isopods Nerocila acuminata and Cymothoa oestrum , and the copepod Paralebion pearsei , are found on the external surfaces of tarpon. Commensal remoras often attach themselves to large tarpon and go along for the ride.

Economic Importance for Humans: Positive

Tarpon mainly benefit humans through recreational activities. In Florida, tarpon are a very important game fish, bringing in millions of dollars annually through charter fishing trips. In some areas, Megalops atlanticus is marketed for its flesh. It is considered a delicacy in South America despite the fact that it is very bony. Large scales of tarpon are used as ornamentation on home decorations and are also used in the manufacturing of artificial pearls.

• Positive Impacts
• food food
• body parts are source of valuable material
• ecotourism ecotourism

Economic Importance for Humans: Negative

There have been a few reported cases of ciguatera poisoning from eating tarpon. Ciguatera poisoning causes nausea, vomiting, and diarrhea. Neurological signs of poisoning include headache and temperature sensitivity and cardiovascular signs can include arrhythmia and reduced blood pressure. There have also been reports of injuries and even deaths to sport fishers attempting to catch tarpon. These fish are very large and have lots of thrashing power when hooked on a fishing line. When pulled into a boat they can thrash their bodies around vigorously and injure the angler. It is best to wear out the fish before pulling it on board to avoid any injury.

• Negative Impacts
• injures humans
  • carries human disease

Conservation Status

The effects of catch and release fishing programs on Megalops atlanticus are not yet fully understood. Releasing tired fish may make them unable to recover quickly. Tarpon may then die from oxygen deprivation or become easy prey for predators. Permits are now being issued to anglers who intend to catch and kill these fish. For a small permit price, two tarpon per licensed angler are allowed to be caught and killed each day. The angler must also report information on where the fish was caught and its size to the Florida Marine Research Institute for further tarpon research. This permit program has greatly reduced the number of tarpon killed over the past few years. In 1989, just before the permit program was instituted, it is estimated that 342 tarpon were caught and killed by anglers. In 1998, the number of tarpon caught and killed by anglers decreased to 70.

Commercial harvesting of M. atlanticus is not permitted.

Additional Links

Encyclopedia of Life

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Jennifer Burnham (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.

References

Hill, K. 2002. "Smithsonian Marine Station at Fort Pierce: Megalops atlanticus" (On-line). Accessed October 13, 2005 at http://www.sms.si.edu/irlspec/Megalo_atlant.htm .

Luna, S., R. Reyes, R. Froese. 2005. "Species Summary: Megalops atlanticus" (On-line). Accessed October 13, 2005 at http://fishbase.org/Summary/SpeciesSummary.php?genusname=Megalops&speciesname=atlanticus .

Morey, S. 2000. "Biological Profiles: Tarpons" (On-line). Accessed October 13, 2005 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/Tarpon/Tarpon.html .