Throughout history, sailors have made claims to spotting half-woman, half-fish creatures known as mermaids. Ancient mythology tells of sea nymphs who would lure sailors into shipwrecks with mesmerizing songs – they were known as sirens. Today that name is given to a group of gentle, aquatic mammals that may very well have inspired both stories.
Sirenians are an order of the animal kingdom that comprise the only completely aquatic mammals that are herbivores. Because of their specific plant-based diet, all sirenians are found throughout the tropic and subtropic regions in relatively shallow waters where sunlight can penetrate and stimulate plant growth. They feed primarily on sea grass and other aquatic vegetation. Commonly these creatures are known as manatees.
There are 4 species of sirenians found today. These include the Amazonian manatee, the West African Manatee, the West Indian Manatee and the Dugong.
The dugong is a unique species of sirenian, unlike their manatee cousins that possess rather large, round paddle-shaped tails, the dugong has a notched tail fluke – similar to that of a dolphin. Dugongs are also only found in the shallow, salt waters of the West Indo-Pacific regions – most notably off the northern coast of Australia.
The remaining manatee species all share a similar build – with a large round torso tapering to their familiar paddle-shaped tail. The have no external discernible neck and like tree sloths the only possess 6 vertebrae. They may weigh up to 1,200 pounds and average around 10 feet long.
The Amazonian species is the smallest of the manatees growing up to 9 feet in length. Several characteristics distinguish it from the other two species. It usually has whitish patches on its underside and is only found in freshwater rivers and lakes of South America.
The West African manatee is very similar in size and appearance to the West Indian manatee and lives in similar habitat. Both species inhabit rivers, bays, canals, estuaries, and coastal areas rich in sea grass and other vegetation.
Both species can live in fresh, salt, and brackish waters. They are able to maintain the correct balance in their bodies through an internal regulation system that works with the kidney to make sure salt concentrations never get too high.
It is believed that West Indian manatees require some access to freshwater in order to stay hydrated, but they are able to move freely between extremes in their habitats.
The West Indian Manatees are comprised of two subspecies: the Florida Manatee and the Antillean Manatee.
Antillean manatees are found in shallow coastal waters throughout the Caribbean and Gulf of Mexico, their most important habitat is found along the coast of Belize, where they dwell in rivers, lakes, lagoons, and coastal marine environments. The Dallas World Aquarium is home to one of these endangered creatures.
The Florida Manatee is perhaps the most familiar species. They are a migratory species the may travel up the eastern US coast as far north as Rhode Island and along the shores of the Gulf of Mexico as far away as Texas. Most will migrate into Florida waters in large groups – known as an aggregation – during the winter months. There they are known to remain close to natural spring sources or outlets from coastal power plants – where the waters remain warm year round.
They may be found in any waterway over 3 feet deep and connected to the coast. They prefer waters with temperatures above 70°F. Florida manatees rarely venture into deep ocean waters. However, they have been spotted as far offshore as the Dry Tortugas Islands, approximately 50 miles west of Key West.
One manatee known as “Chessie” traveled 2,000 miles from Florida to Rhode Island, and back in 1996. Chessie migrated further north and covered a greater distance than any manatee ever documented.
The manatees small, flexible pectoral flippers are used for steering, touching, scratching, and even embracing. The West Indian and West African species have 3 or 4 fingernails – similar to the toe-nails on an elephants feet – on their flippers. Amazonian manatees and dugong, however, lack these nails. Internally, the bone structure of a manatee’s flipper is similar to toothed whales and seals – each has five digits covered by thick skin.
Manatees are quite agile and maneuver well under water. Often considered to be slowing moving animals, Florida manatees have been observed swimming at speeds up to 15 mph for short bursts, but usually cruise about around 2 – 6 mph or less.
Manatees are quite buoyant and use their horizontally placed diaphragm and breathing to control their buoyancy, their solid rib bones also help them to remain on the bottom to graze. They usually surface every 2-3 minutes to breathe though they can remain submerged up to 20 minutes. Studies show that manatees renew about 90% of the air in their lungs in a single breath (humans renew only about 17%).
The closest living relatives to the manatee and dugong is considered to be the elephant. Like their elephant relatives, manatee continuously replace their teeth throughout their lives with the older teeth at the front falling out and new teeth growing in at the back of their mouth. Manatee also have ridged pads at the front of the upper and lower jaws which aid in crushing plant materials.
Female manatees usually have one calf every two to five years and the calf then stays and nurses for two years. Calves nurse from their mother’s teats, which are found right where the forward limbs meet the body. The calves also can start nibbling on plants at only a few weeks old.
Manatees have no true natural predators but they are at risk from both natural and man-made causes of injury and mortality. Exposure to red tide, cold stress, and disease can all affect manatees. Man-made threats to manatees include boat strikes, crushing by flood gates or locks, and entanglement in or ingestion of fishing gear.
In addition to Manatees and Dugongs, another member of the order Sirenia is the large ocean dwelling mammal known as the Steller’s Sea Cow. This creature once inhabited the cold waters of the Bering Sea between Alaska and Russia.
This impressive animal was only described in 1741 – having a large torso, a whale like tail and a small, disproportionate head it was the largest sirenian on record. The Steller’s Sea Cow grew up to 30 feet in length and weighed up to 8,800 pounds. Unfortunately it was hunted to extinction within 27 years of its discovery.
To protect and ensure the ongoing survival of the Florida manatee, the US Fish and Wildlife Service established the Manatee Rescue, Rehabilitation and Release Program. The program’s goal is to rescue and treat sick or injured manatees and then release them back into the wild.
Rescued animals needing additional medical treament are taken to one of the federally permitted manatee critical care facilities: the Jacksonville Zoo, the Miami Seaquarium, SeaWorld Florida and Zoo Tampa at Lowry Park.
Following treatment, these manatees are transferred to other Program partner facilities for additional rehabilitation while awaiting release. These include the EPCOT’s The Seas at Walt Disney World Resort, the South Florida Museum, and the Ellie Schiller Homosassa Springs State Wildlife Park plus two zoological facilities in Ohio – the Cincinnati Zoo and the Columbus Zoo – the only facilities outside the state of Florida to participate in the rehabilitation program.
Among the tropical waters of the western Atlantic and Carribbean seas lives a slender, streamlined hunter. Known for its quick speeds and intimidating appearance, this daytime hunter is often feared. Capable of growing up to 6 feet long and weighing up to 100 pounds, this top predator is the Great Barracuda.
The Great Barracuda is easily recognized by its long, tubular shape with shiny blue-gray coloration above, fading to silver and white below, dark bars on its upper side and usually with dark spots on its lower sides. It is the dark spots that often help distinguish the Great Barracuda from other barracuda species.
Very muscular and built for speed, it is one of the fastest fish in the sea. Due to its size and speed – which few animals can match – adult Great Barracudas have no natural predators, though juveniles will sometimes be preyed upon by sharks, tuna and grouper.
Barracudas have a large mouth containing two sets of teeth. The outer row of small, razor-sharp teeth are for tearing, and the inner set of larger teeth for piercing. The long needle-like teeth fit into holes in the opposing jaw, which allows the barracuda to fully close its mouth.
Barracudas have a large gape, paired with their deadly bite they are able to feed on large fishes by chopping them in half. Some of the teeth of the great barracuda point backwards to prevent slippery fish from escaping once they are seized. An opportunistic predator, great barracuda are generally a diurnal fish, that locate their prey largely by sight.
Great barracuda are the largest of the 20 barracuda species found among coral reefs worldwide. They may also reside in the open ocean, usually at or near the surface, although they are at times found at depths to 300 feet. While some species of barracuda are schooling fish, the Great Barracuda tends to be solitary and territorial but juveniles are often found in small aggregations among mangroves and shallow seagrass beds, habitats that offer some protection from predators.
Great barracuda are common sights to many divers and snorkelers. The fish is naturally inquisitive and is often attracted to shiny objects and reflections – which may resemble the flashing sides of possible prey. There is a belief that barracuda may attack a person who has some type of silver, shiny object – however Great Barracuda are not typically known to attack unprovoked, and in most cases, the keep their distance.
While the threat of an attack is real, the greatest danger they pose to humans is when they are eaten. Great Barracuda are not a commercial fish but many anglers consider them a great sport fish. Due to the reef fish they feed upon and the high content of algae in the diet of their common prey, barracuda meat can contain a toxin that is harmful to humans.
The timing and location of barracuda spawning has not been well documented. It is believed that spawning takes place in deeper, offshore waters. During the spawning, eggs are released and fertilized in open waters and dispersed by the ocean currents. Some studies indicate that barracuda may be seasonal spawners and in the Florida Keys they are believed to breed in the spring.
As with many apex predators, the Great Barracuda fills an important role in its native habitats. Helping keep the population of other species in check and maintaining the overall balance in many of the world’s reef ecosystems.
The sawfish is a group of 5 species that belongs to a group of fishes called elasmobranchs that includes other rays and sharks. They are named after their most distinguishing feature – their extended, thin, narrow snout, or rostrum, which is lined with many short teeth giving the appearance of a saw, sawfishes are sometimes known as carpenter sharks.
While sawfish have a general appearance and swimming movements like sharks, they are actually a type of ray. Their mouth and 10 gill slits are located on the underside of their head. They breath by intaking water through spiracles on the top of their head which then pushed through the gills for respiration – this allows the sawfish to often lie rather motionless on the sea floor, much like a stingray.
Their signature physical characteristic is an extended snout which can make up as much as 1/3 of the animals length. It is constructed by calcified cartilage and contains a large concentration of Ampullae of Lorenzini – the electroreceptive sensory organs that sharks and rays use to detect prey. Each of the 5 species of sawfish have slightly different rostrums – varying in size, shape and the number and spacing of saw teeth that project from each side.
The saw teeth are actually not teeth at all, but modified scales known as dermal denticles. Unlike the teeth in the mouth, a saw tooth that is completely lost is not replaced; however, if a tooth is only chipped and the base is still intact, it will continue to grow as the animal grows.
The sawfish’s actual teeth, located inside their mouth are small and rounded – said to be similar in appearance to a cobble stoned road.
The sawfish is a nocturnal hunter, often resting on the bottom during the day. They feed on crustaceans, mollusks and other bottom-dwellers as well as schools of fish, such as herring and mullet. They will use their rostrum first to detect prey by their electric signals and then by thrashing it side to side to stun or impale the fish. They may also use their saw as defense against predators, which are usually large shark species.
The five species of sawfish include the Dwarf, the Green, the Knifetooth, the Largetooth and the Smalltooth sawfish. Each species has slight differences in size, tail fin shape and habitat regions – though several are found in the Indian and West Pacific regions of Indonesia..
Dwarf sawfish is one of the smallest species of sawfish growing to a length of 13 feet. They have evenly distributed saw teeth, as many as 27 per side. They are found in the river mouths and estuaries on the coast of northern Australia and parts of Indonesia.
The Green sawfish, also known as the Combtooth, has an uneven distribution of teeth along the rostrum and lacks any type of forked tail fin. They are found in near coastal sand and mud flats as well as deeper waters in the Indonesian region.
Knifetooth, or Narrow sawfish is found in the Indian and West Pacific oceans from the Red Sea to Australia and as far north as South Korea. It is one of the most recognizable of the species since it lacks any saw teeth on the lower half of the snout and it possesses a distinctly forked tail fin.
Largetooth sawfish are sometimes known as Freshwater sawfish but they do inhabit salt water habitats as well as the freshwater shoreline rivers of Australia. This species is sometimes found on display in accredited aquarium facilities such as the Dallas World Aquarium, the Aquarium of the Pacific in Long Beach California and the Georgia Aquarium.
Smalltooth sawfish are olive gray to brown on top and have a white underside. Smalltooth sawfish have 22 to 29 teeth on each side of their snout. The smalltooth species is not as common but can also be seen in some public aquarium exhibits.
Smalltooth sawfish look very similar to largetooth sawfish and it can be hard to tell the two species apart. The smalltooth has a long but narrow rostrum with smaller teeth toward the tip and larger sized teeth closer to their head. The largetooth sawfish has a slightly broader rostrum with teeth that are typically of the same size and spaced evenly apart except at the very tip.
Both species live in coastal waters and brackish estuaries – semi-enclosed areas where rivers meet the sea. These shallow estuaries serve as important nurseries for newborn and juvenile sawfish.
While both the largetooth and smalltooth varieties once inhabited larger coastal regions of their habitats – today the largest viable population of largetooths are found primarily near Australia and the smalltooth variety is found in the Southwestern coast of Florida and parts of the Bahamas.
Smalltooth sawfish are generally regarded as gentle and harmless to humans, but they have been known to cause serious injuries if trapped by fishing hooks or nets.
Sawfish reproduce by internal fertilization and females give birth to live young. Smalltooth sawfish embryos grow inside the mother during the gestation period which is believed to be one year. Female smalltooth sawfish can give birth to 7–14 young pups measuring 2 to 2 and half feet long.
The pups are born with fully developed saws. To prevent injury to the mother and siblings, the saw teeth of the young fish are covered by a thick gelatinous tissue which completely disappears about two weeks after birth. The newborn sawfish typically double in size during their first year and reach sexual maturity at around 7 years and when they’ve grown to about 11 feet long.
Sawfish are sometimes confused with another species found in the world’s oceans – the saw shark, which is actually – a shark. Unlike the sawfish the saw shark has a long narrow snout that also features long, finger-like barbels hang from their rostrums and their gills (like other sharks) are located on the sides of the animals head. Saw sharks inhabit the western Pacific and Indian oceans – they are often found in the coastal waters of Japan.
Sawfish are culturally important to many native societies around the world. They are considered symbols of strength, spirituality, and even creation.
Certain Aboriginal clans from Northern Terriorty of Australia believed that some ancestors came in the form of sawfish and used its saw-like rostrum to carve out rivers and landscape.
The Kuna, native to the Caribbean coast, believe that sawfish protect mankind, and will help them fight off dangerous sea creatures.
Other societies have viewed sawfish as supernatural beings that bring prosperity and good luck to their communities.
Today, sawfish populations worldwide are in danger of extinction and are considered critically endangered. The population of smalltooth sawfish in the United States has severely declined over the last century and in 2003 became the first marine fish to receive federal protection as an endangered species under the Endangered Species Act.
Special thanks to the following organizations for their education, research and conservation programs that provided information for this episode:
Cincinnati Zoo & Botanical Garden
Columbus Zoo & Aquarium
Dallas World Aquarium
Florida Fish and Wildlife Conservation Commission
Guy Harvey Ocean Foundation
Save The Manatee.org
Sawfish Conservation Society
SeaWorld’s Animal Guide
U.S. Fish and Wildlife Service
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