Megalops atlanticus Valenciennes in Cuvier and Valenciennes, 1847
Family: Megalopidae
Common names: tarpon
Synonyms: Tarpon atlantica Valenciennes, 1847
Megalops atlanticus image
Megalops atlanticus  

Species Description: Tarpon (Megalops atlanticus) are large, deep-bodied fish commonly found in coastal and inshore waterways. Body color on the dorsal surface is generally dark blue or green to black, The sides and ventral surface are silver. Pelvic fins are abdominal, the caudal fin is deeply forked, and the single dorsal fin is short with a long, filamentous terminal fin ray. The scales of this species are large and cycloid, with 40-48 lateral scale lines. The mouth is large, with a protruding lower jaw. Members of the family Elopidae have pronounced gular plates that span the lower jaw bones on the underside of the head.

Regional Occurrence: Megalops atlanticus occurs in the Western Atlantic Ocean from Nova Scotia to Brazil, including Bermuda, the Caribbean, and the Gulf of Mexico. It is most common south of the Carolinas.

IRL Distribution: Tarpon are distributed throughout the Indian River Lagoon.

Age, Size, Lifespan: M. atlanticus can attain a size of 8 feet in length (2.4 m), weighing as much as 280 pounds (128.4 kg). Tarpon are sexually dimorphic, with females growing larger than males. A study by Crabtree et al. (1995) showed that of the 1,469 tarpon examined, mean fork length (FL) of large females sampled from the recreational fishery was 167.7 cm FL. Mean fork length among males sampled was 144.7 cm. Otolith examination shows that tarpon can also be extremely long-lived. Crabtree et al. (1995) reported that the oldest female tarpon examined in their study, which measured 204.5 cm in fork length, was approximately 55 years old, while the oldest male, which measured 171 cm fork length, was 43 years old.

Abundance: Tarpon are common from the Atlantic coast of central Florida, around the Florida peninsula, the Gulf of Mexico, and the Caribbean. On the Western Florida coast, they are often observed in large schools 2-5 km offshore during the mid-summer spawning season. They become far less common north of North Carolina (Boschung et al. 1983), however, tarpon are known to occur as far north as Nova Scotia.

Locomotion: Estimates of swimming speeds of tarpon in open water ranged from approximately 1 - 4 knots (Edwards 1998).

Reproduction: Male tarpon in Florida waters reach sexual maturity between 90 - 117.5 cm FL, while females mature at approximately 128.5 cm FL (Crabtree et al. 1997). Age at sexual maturity is estimated to be between 7 - 13 years of age (Garcia and Solano 1995). However, in Costa Rica, tarpon reach sexual maturity at a younger age than do Florida tarpon, and apparently do not grow to as large an adult size (Crabtree et al. 1997).

Tarpon are highly fecund, with large females estimated to produce over 12 million eggs (Garcia and Solano 1995). Crabtree et al. (1997) estimated fecundity in Florida tarpon to range from 4.5 - 20.7 million oocytes per female, with larger fish producing proportionally more eggs. Data suggest tarpon spawn seasonally in Florida and are multiple spawners (Crabtree et al. 1997). Tarpon in Florida and the eastern Gulf of Mexico make extensive spawning migrations from inshore waters to offshore spawning grounds from May through July, with spawning occurring from May - August (Crabtree et al 1995, 1997). Large schools of tarpon, consisting of 25 - 200 individuals have been observed offshore in Florida waters during he early summer (Crabtree et al. 1992). In Costa Rica, spawning does not appear to be seasonal, and ripe females are commonly captured in all months (Crabtree et al. 1997).

It has been suggested that lunar phase may be an important trigger for spawning activity. Data from Crabtree et al (1995) show that successful hatching of tarpon eggs occurs 3 - 5 days following a full moon, and 0 - 7 days following a new moon.

Embryology: Vitellogenic (yolked) eggs average 0.7 mm in diameter (Crabtree et al 1992). Eggs are spawned in offshore waters and hatch into leptocephali larvae after approximately 2 - 3 days. Leptocephali are distinguished by their elongate, compressed body form, which consist primarily of an acellular, mucinous matrix (Crabtree et al 1992). They also have slender, fang-like teeth, which are prominent in the head region. Leptocephali range in size from approximately 5.5 - 24.4 m standard length (SL) (Crabtree et al. 1992).

The leptocephalus stage persists for 2 - 3 months (Crabtree 1995). during this period, leptocephali are transported on currents from offshore waters back to coastal waters, and eventually into estuaries where they complete development. Metamorphic larvae are most often found in mangrove-lined estuaries and in Spartina saltmarshes (Harrington 1958, Crabtree et al. 1995).

Physical Tolerances: Tarpon are obligate air breathers (Edwards 1998) and are physostomous, meaning they possess a duct that connects the gas bladder to the esophagus. This anatomical feature allows the gas bladder to act as a lung, and enables tarpon to live in oxygen-poor waters (Bond 1996).

Trophic Mode: Tarpon occurring in Florida and throughout the Gulf of Mexico feed primarily on species such as sardines, anchovies, mullet, snook, cichlids, and crabs (Whitehead and Vergara 1978). In a Costa Rican study (Chaverri 1994), smaller juvenile tarpon (<9 cm) fed primarily on copepods (40%), insects (23%) and detritus (26%) while larger juveniles (>9cm SL) fed primarily on fishes (30%), and insects (30%). A study conducted in Columbia (Catano and Garzon-Ferreira 1994) showed that smaller tarpon (12 - 53 cm) have diets which very according to habitat type and season. In spring, (March through May), tarpon sampled from river mouths in Columbia fed primarily on mullet (39%) and other fishes (43%).

However, in fall (October to December), mollies and other poecilids composed the bulk of the diet (56%), with mullet (8%) and insects (17%) also included. Tarpon sampled from swamps in Columbia showed a similar pattern. In spring, mullet (37%), insects (21%) and penaeid shrimp (11%) composed the bulk of the diet; but in the fall, poecilids (65%) and insects (19%) are more prominent.

Habitats: Tarpon occur in a variety of habitat types, from freshwater rivers and lakes to offshore waters. However, large tarpon, often the target of an economically important recreational fishery are found primarily in estuaries and nearshore coastal waters (Crabtree et al. 1995, Amos and Amos 1997). Tarpon spawn offshore, but larvae develop inshore.

Benefit in IRL: The tarpon is highly prized as a recreational fish due to its tremendous strength and fast swimming speed. However, it is not valued as a food fish.

Economic Importance: The Indian River Lagoon generates approximately 731 million dollars annually to the Florida economy. Of this, approximately 465 million dollars is generated by recreational activities such as sport fishing, boating, water sports, hunting, and ecotourism activities (data provided by St. Johns River Water Management District). As the tarpon is among the most important of Florida's recreational species, it directly contributes to Florida's economy.

Since 1989, implementation of a permit system in the tarpon fishery requires anglers to pre-purchase a $50.00 permit in order to harvest a tarpon. This process has resulted in a tremendous increase in catch-and-release fishing for this species, with approximately 100 fish per year legally harvested (Crabtree et al. 1995). Data from Edwards (1998) shows that release mortality in the tarpon fishery is low when fish are hooked in the jaw, are brought to the boat and released within a relatively short period of time, and are not removed from the water while being released. Fish handled in this manner were shown to recover quickly and resume normal activities within a short period of time.

Catano, S., J. Garzon-Ferreira. 1994. Ecologia tropica del sabalo (Megalops atlanticus) (Pisces: Megalopidae) en el area de Cienaga Grande de Santa Marta, Caribe Columbiano. Rev. Bio. Trop. 42(3):673-684.

Chaverri, D.C. 1994. Ecologia basica y alimentacion del sabalo (Megalops atlanticus) (Pisces: Megalopidae). Rev. Bio. Trop. 42(1/2):225-232.

Crabtree, R.E., 1995. Relationship between lunar phase and spawning activity of tarpon (Megalops atlanticus), with notes on the distribution of larvae. Bull. Mar. Sci. 56(3):895-899.

Crabtree, R.E., E.C. Cyr, R.E. Bishop, L.M. Falkenstein, J.M. Dean. 1992. Age and growth of tarpon (Megalops atlanticus) larvae in the eastern Gulf of Mexico, with notes on relative abundance and probable spawning areas. Env. Bio. of Fishes 35:361-370.

Crabtree, R.E., E.C. Cyr, J.M. Dean. 1995. Age and growth of tarpon (Megalops atlanticus) from South Florida waters. Fish. Bull. 93(4):619-628.

Crabtree, R.E., E.C. Cyr, D.C. Chaverri, W.O. McLarney, J.M. Davis. 1997. Reproduction of tarpon (Megalops atlanticus) from Florida and Costa Rican waters and notes on their ages and growth. Bull. Mar. Sci. 61(2):271-285.

Edwards, R.E. 1998. Survival and movement patterns of released tarpon (Megalops atlanticus). Gulf of Mexico Science 1:1-7.

Whitehead, P.J.P., R. Vergara. 1978. Megalopidae. In: W. Fischer (ed.) FAO species identification sheets for fishery purposes. Western Central Atlantic (Fishery Area 31) Volume 3. FAO, Rome.

Megalops atlanticus image
Megalops atlanticus