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.
Synonymy:
Tarpon atlantica (Valenciennes, 1847)
Other Taxonomic Groupings:
Superclass Osteichthyes
Subclass Neopterygii
Infraclass Teleosti
Superorder Elopomorpha
II. HABITAT AND DISTRIBUTION
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.
III. LIFE HISTORY AND POPULATION
BIOLOGY
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).
IV. PHYSICAL TOLERANCES
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).
V. COMMUNITY ECOLOGY
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 SL) 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.
VI. SPECIAL STATUS
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.
VII. BIBLIOGRAPHY
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.
Report by: K. Hill,
Smithsonian Marine Station
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