Marine Biology Notes

7 - Marine Turtles, Mammals and Seabirds

Marine Reptiles

Four types of marine reptiles exist today:

1. Sea Turtles

2. Sea Snakes

3. Marine Iguana

4. Saltwater Crocodile

Sea Turtles

• All species of sea turtles are threatened or endangered

• Endangered means that a species is under direct threat of species survival (extinction is a definite threat)

• Threatened means that the species may become endangered

• Both designations give these species protection under the Endangered Species Act

Sea Turtles

• Seven or eight species of sea turtles exist today:

– Leatherback sea turtle

– Loggerhead sea turtle

– Hawksbill sea turtle

– Olive ridley sea turtle

– Kemps ridley sea turtle

– Australian flatback sea turtle

– Green sea turtle – some biologists recognize two species of green turtles, the Pacific green turtle and the Atlantic green turtle (this is the reason for the 7 or 8 species discrepancy)

Sea Turtles

• Structurally, sea turtles have an upper shell known as the carapace and a lower shell known as the plastron

• The ribs are expanded in size and fused to their shell

• All sea turtles have powerful jaws, but no teeth

• Like other reptiles, sea turtles are poikilothermic (internal temperature varies) and ectothermic although the leatherback sea turtle is so large that its body temperature is normally several degrees above the ambient water temperature

Sea Turtles

• Sea turtles breed at sea

• Internal fertilization occurs – males use their long tails as well as the claws on the front flippers to “grip” the female during reproduction

• Females can store sperm

• One clutch (group) of eggs can have multiple paternity – males and females are not monogamous

Sea Turtles

• Females normally breed every 2-4 years

• These females must return to land to deposit their eggs near the dune line (above the high tide)

• Females dig a hole in the sand using only the back flippers

• During their breeding year, females may lay up to 7 clutches of eggs

• Each clutch of eggs normally has an average of 120 eggs, although large variations in these numbers have been recorded

Sea Turtles

• The eggs have a typical incubation period of around 60 days – although this varies according to air temperature.

• Warmer temperatures means eggs will develop faster, colder temperatures elongate the incubation process (a range of 45-75 days is not unusual)

• The eggs are very leathery at the time the mother lays the eggs

• As they incubate, they become more brittle, making it easier for the hatchlings to escape the egg

Sea Turtles

• Sea turtles, like many reptiles, exhibit temperature dependent sex determination

• This means that the gender of the hatchling is not genetically predetermined

• Gender is determined by the temperature of the environment in which the egg was incubated

• For each species, there is a “pivotal” temperature that will generate 50% males and 50% females; temperatures higher than pivotal will produce more females, temperatures lower than pivotal will produce more males

Sea Turtles

• The smallest of the sea turtles is the Kemps Ridley at around 100 cm and just over 100 pounds

• The Kemps Ridley was long thought to be a hybrid of other species of sea turtles because for MANY years, no nesting site for the Kemps Ridley turtles was ever seen

• Then, one nesting site was finally located in Rancho Nuevo, Mexico

• Due to the critically endangered status of this species, this nesting site is now jointly managed by the US and Mexican government wildlife agencies

Sea Turtles

• The green sea turtle is the only “vegetarian”

• It is called the green sea turtle because the fat in its body is slightly green as a result of its diet of seagrasses and algae

• Green sea turtles are normally considered tropical nesting turtles, but green sea turtles have nested regularly in Florida as long as records have been kept

Sea Turtles

• Interestingly, green sea turtles are now nesting as far north as North Carolina

• Each summer, dozens of nesting reports for green sea turtles come in from all over the NC coast

• The first report of green turtle nesting in NC occurred in the 1950’s

• In the 1980’s, nest reports started climbing

Sea Turtles

• The loggerhead sea turtle is the least vulnerable of the sea turtles with regards to numbers – its status is listed as threatened

• Like the kemps ridley and the olive ridley, the loggerhead feeds mainly on invertebrates such as crabs and molluscs

Sea Turtles

• The leatherback is the largest of the sea turtles reaching over 6 ft and 1000 lbs

• These turtles feed often on jellyfish but can dive to deep depths to feed on other prey items

• The hawksbill is a tropical species of sea turtle

• This species feeds mainly on corals, sponges and associated invertebrates

The Leatherback Sea Turtle

The Loggerhead Sea Turtle

The Hawksbill Sea Turtle

The Green Sea Turtle

Sea Snakes

• There are 55 species of sea snakes

• These snakes are found only in the Indian and Pacific Ocean

• These snakes have a laterally flattened body with a paddle-like tail for propulsion through the water

• Most species are 3-4 feet in length as adults

Sea Snakes

• Sea snakes breed at sea and most species are ovoviviparous

• A few species still return to land to lay eggs

• Bites from sea snakes can be fatal for humans– the sea snakes are related to the cobra and have a powerful venom

• Fortunately, sea snakes are not known to be aggressive

• Sea snakes are carnivorous and mainly feed on fish

Saltwater Crocodile

• This species is found in Australia, the Indian Ocean and some Western Pacific Islands

• It can be found in estuaries, mangrove swamps, rivers and the open ocean

• It is a predatory species that eats all types of prey items including humans

• The saltwater crocodile is a large species reaching lengths of over 30 feet (although individuals over 20 feet are rare)

• This species is not secretive like the American Crocodile, but is an aggressive hunter

Marine Iguanas

• Marine iguanas live on the Galapagos Islands

• While they are called marine, they only spend a portion of their time in the water

• They dive to feed on seagrass near the shore

• A large portion of their day is spent basking on the shore to warm up from their dives in the cold water surrounding the Galapagos

Seabirds

• Seabirds, like mammals, are able to maintain a constant body temperature derived through metabolic means

• The feathers that cover the body are coated with an oil from glandular secretions

• This oil helps to waterproof the body

• The hard shelled egg provides more protection than the leathery shell of reptiles

Seabirds

• Many species of seabirds are colonial nesters - they nest in large colonies of individuals near the shore – some on cliffs, others in low shrubs or trees, others directly on the ground

• Some species are monogamous and mate for life

• Birds are well known for their protection of young and other behaviors such as preening and complex rituals for selecting a mate

Seabirds Penguins

• Penguins are flightless with the wing modified into a flipper-like structure

• Penguins spend a great deal of time in the marine environment searching for prey

• Most species of penguins live mainly in Antarctica

• They have a layer of fat and trap air in the feathers to help them survive these cold environments

• Males and females share parenting responsibilities

Seabirds

• Other species of seabirds do exist such as shearwaters, petrels, albatross, frigate birds, pelicans and cormorants

• However, none of these birds are adapted to the marine environment in the same way that penguins are

• Even those that spend long periods of time at sea still have features very much like terrestrial birds

Albatross – above Cormorant - below

Frigate – above Petrel - below

Characteristics of Mammals

• 4600 species

• Skin possesses hair

• Homeothermic

• Mostly viviparous with placenta

• Mammary and other glands

• Larger brain in relation to body size

• Many sexually dimorphic (males and females look different in size, coloration, features, etc)

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Major Groups of Marine Mammals

1. Pinnipedia – seals, sea lions and walrus

2. Carnivora – sea otter and polar bear

3. Sirenia – dugong and manatees

4. Cetacea – whales, dolphins and porpoises

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Order Pinnipedia • Below is a comparison of sea lions/fur seals versus true seals.

• Notice the external ear of sea lions/fur seals (not present in seals).

• Also notice that sea lions/fur seals can rotate the rear limbs forward for more efficient locomotion on land.

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Order Pinnipedia

Seals:

• 19 species

• Most live in cool or cold water

• Monk seals are the exception – they love in warmer waters

• Hawaiian and Mediterranean monk seals are endangered

• Caribbean monk seals have not been seen since the 1950’s

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Order Pinnipedia FAST FACTS ON SEALS: • SIZE: Range extensively in size from 110-580 cm (3.6-19 ft.); males

are approximately the same size as females • WEIGHT: Range in weight from 50-5,000 kg (110-11,023 lb) • DIET: Generally eat various fish, shell fish and cephalopods • GESTATION:270-350 days; some species have delayed implantation • NURSING DURATION: 10-80 days • SEXUAL MATURITY: Varies by species (Males generally 4-6 years;

females generally 4 years) • LIFE SPAN: Varies; up to 45 years in ringed seals (Pusa hispida) and

14 years in male elephant seals (Mirounga leonina) • RANGE: Coastlines and ice fronts throughout the world except the

Indian Ocean. Some species are found in inland lakes. • HABITAT: Prefer coastal areas with shallow waters near abundant

food sources.

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Order Pinnipedia

FAST FACTS ON SEA LIONS/FUR SEALS:

• DESCRIPTION: Elongated, fusiform body (tapering at both ends) with a small tail. The limbs are flattened and thick. Forelimbs are long and oar-like. Their snouts are blunt and have numerous sensitive whiskers.

• SIZE: Range in size from approximately 110-330 cm (3.6-10.8 ft.); males are much larger than females.

• WEIGHT:21.5-1,000 kg (47-2,205 lb)

• DIET: Generally various fish species and invertebrates

• GESTATION:10-12 months including period of delayed implantation

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Order Pinnipedia

FAST FACTS ON SEA LIONS/FUR SEALS: • NURSING DURATION: 3-36 months • SEXUAL MATURITY: Varies by species (Male,

generally 4-6 years; female, generally 4 years) • LIFE SPAN: Typically ranges from 15-25 years; rarely

exceeds 30 years • RANGE: Coast of northeastern Asia, western North

America, South America, southern Africa, southern Australia, New Zealand and many southern islands

• HABITAT: Prefer coastal areas with shallow waters near abundant food sources

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Order Pinnipedia FAST FACTS ON WALRUSES: • DESCRIPTION: Walruses are very distinctive having a

large, robust, fusiform body that is usually reddish-brown in color. On their head region, walruses lack external ear flaps, have hundreds of short, vibrissae (whiskers), and both males and females possess large tusks. Like other pinnipeds, the fore and hind limbs of a walrus are modified into flippers.

• On land, walruses are capable of rotating their hind flippers under their pelvic girdle to walk on all fours in a similar manner to sea lions. Adult males are slightly larger than females with longer and stouter tusks.

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Order Pinnipedia FAST FACTS ON WALRUSES:

• SIZE: The Pacific subspecies is larger than the Atlantic. Newborn calves are about 95-123 cm (3-4 ft.) long. MALE2.7-3.6 m (9-12 ft.) FEMALE2.3-3.1 m (7.5 to 10 ft.)

• WEIGHT: Newborn claves weigh about 45-75 kg (99-156 lb.)

• DIET: Mainly bivalve mollusks such as clams; also other benthic invertebrates such as marine worms, snails, sea cucumbers, squids, and crabs. May occasionally prey upon fish such as polar cod and scavenge on seal carcasses. There are rare cases of very large, male walruses that habitually prey upon seals, especially ringed and bearded seals.

• GESTATION: 15-16 months, including a period of delayed implantation

• NURSING DURATION: 2 or more years (wean)

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Order Pinnipedia

FAST FACTS ON WALRUSES:

• SEXUAL MATURITY: MALE8-10 years; successful reproduction probably not until about 15 years; FEMALE 5-6 years; successful reproduction at about 10 years

• LIFE SPAN: 16-30 years

• RANGE: Arctic Sea - both Pacific and Atlantic (Bering, Laptev and Chukchi seas)

• HABITAT: In relatively shallow water - generally not more than 80 m (262 ft.) deep. Hauls out on ice floes, pack ice and small rocky islands when ice is not present.

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Order Carnivora FAST FACTS ON SEA OTTERS: • DESCRIPTION: sea otters do possess the fine, dense fur coats.

Their forefeet are small and dexterous with retractile claws and the flipper-like hind feet are broad and webbed. Juvenile sea otters tend to be a uniform dark-cinnamon brown while adults develop lighter gray or buff coloration on their heads. In general, mature male sea otters tend to be slightly larger than females of their respective subspecies.

• SIZE: Alaskan sea otters are slightly larger than California sea otters. Male Alaskan sea otters reach lengths up to 148 cm (58 in.) and male California sea otters average 122 cm (4 ft.) Female Alaskan sea otters measure up to 140 cm (55 in.) in length

• WEIGHT: Mature male Alaskan sea otters weigh up to 39 kg (85 lb.), while California sea otters average 29 kg (64 lb.) Adult female Alaskan sea otters can reach weights of up to 33 kg (72 lb.), and female California sea otters weigh on average 20 kg (44 lb.)

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Order Carnivora

FAST FACTS ON SEA OTTERS:

• DIET: A sea otter has a metabolic rate much higher than most mammals of similar size, and must consume large quantities of food. Adult sea otters may eat as much as 9 kg (20 lb.) of food each day. Among their food preferences are sea urchins, crabs, abalone, clams, mussels, octopus, and fishes. Most sea otters specialize in only a few types of the available food items.

• GESTATION: Approximately 4-9 months with an average of 6 months; probably includes a 2-3 month period of delayed implantation

• ESTRAL PERIOD: The reproductive cycle in California sea otters is about 12 months. If a female's pup doesn't survive, she may experience postpartum estrus.

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Order Carnivora FAST FACTS ON SEA OTTERS:

• NURSING DURATION: Approximately 6-8 months (wean)

• SEXUAL MATURITY: Approximately 5-6 years in males and 4 years for females

• LIFE SPAN: On average, 10-15 years.

• RANGE: In coastal regions throughout the eastern North Pacific Ocean.

• HABITAT: Typically found in coastal waters no further away than 1 km (0.6 mi.) from shore. The Alaskan sea otter has a greater tendency to haul out (come to shore) than the California

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Photo of Sea Otter in Typical Habitat – Kelp Community

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Order Carnivora FAST FACTS ON POLAR BEARS: • DESCRIPTION: Polar bears are the largest land carnivore.

They have a thick fur coat that appears white in coloration, but is really translucent. Their black skin color is readily apparent on the nose, eyes, lips and footpads. Polar bears have smaller ears and longer necks than other bears. Adult male polar bears, called boars, are substantially larger than adult females.

• SIZE: At birth, cubs are about 30 cm (12 in.) long; Males typically 2.5-3 m (8.2-9.8 ft.) long; Females typically 2-2.5 m (6.6-8.2 ft.) long

• WEIGHT: Newborn calves weigh about 454-680 g (16-24 oz.); Males weigh 350-650 kg (772-1,433 lb.); Females weigh 150-250 kg (331-551 lb.) 51

Order Carnivora FAST FACTS ON POLAR BEARS: • DIET: Adult polar bears need an average of 2 kg (4.4 lb.)

of fat per day to maintain their weight. Their diet includes mostly ringed and bearded seals and also includes other seal species, walruses, narwhals, beluga whales, whale carcasses, fish, reindeer, birds, eggs, berries and kelp.

• GESTATION: About 8 months; includes about a 4 month period of delayed implantation

• ESTRAL PERIOD: Females are induced ovulators; mating triggers the release of an egg for fertilization

• NURSING DURATION: 18-30 months (wean)

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Order Carnivora

FAST FACTS ON POLAR BEARS:

• SEXUAL MATURITY: Males about 6 years; females about 4 years

• LIFE SPAN: Typically 15-18 years; some have lived over 30 years

• RANGE: Circumpolar arctic

• HABITAT: Inhabit Arctic sea ice, water, islands, and continental coastlines

• POPULATION: Estimated at 21,500-25,000 globally

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Order Sirenia • Trichechus inunguis, the Amazonian manatee. The Amazonian

manatee is the smallest of the manatees. Several physical characteristics distinguish it from the other two species. It lacks nails on its pectoral fins, and usually has whitish patches on its underside.

• Trichechus manatus, the West Indian manatee. There are two subspecies of the West Indian manatee: the Florida manatee (Trichechus manatus latirostris) and the Antillean manatee (Trichechus manatus manatus). These subspecies are distinguished by differences in cranial measurements and by their geographic distribution.

• Trichechus senegalensis, the West African manatee. About the same size and shape of the West Indian manatee, the West African manatee differs in some important respects: position of the eyes, snout, and cranial bones.

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Order Sirenia FAST FACTS ON MANATEES: • The manatee's body is streamlined - full around the

middle and narrowing to a paddle-shaped tail. The true color of a manatee is gray, although it may appear brownish gray.

• Amazonian manatees usually have white or pink patches on the belly and chest. Organisms such as algae, which may grow on the skin of slow-moving individuals, alter the body color and make some manatees look more green or brown.

• West Indian manatees are the species found in the United States.

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Order Sirenia FAST FACTS ON MANATEES: • SIZE: Adult West Indian and West African manatees

average about 3 m (10 ft.) in length. Large individuals may reach lengths of up to 4 m (13 ft.). Amazonian manatees are the smallest of all three species. They are shorter and more slender. The longest specimen measured 2.8 m (9.2 ft.).

• WEIGHT: Average adult weights are approximately 363 to 544 kg (800-1,200 lb.). One particularly large Florida manatee weighed 1,655 kg (3,650 lb.). Females are generally larger than males. A particularly large Amazonian manatee individual weighed 480 kg (1,058 lb.).

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Order Sirenia FAST FACTS ON MANATEES: • DIET: Manatees are primarily herbivores. They feed on a wide

variety of submerged, emergent, floating, and shoreline vegetation. Manatees consume about 4% to 9% (15 to 49 kg or 32-108 lb. for an average adult manatee) of their body weight in wet vegetation daily. Manatees have occasionally been seen to eat foods other than plants. Antillean manatees have been known to eat fish from nets and West African manatees have been known to eat clams. Some Amazonian manatees living in deep bodies of water apparently fast during dry seasons (November and December) when water levels drop as much as 9 to 15 m (30-50 ft.), eliminating their access to vegetation. Because manatees have a very low metabolic rate, it is speculated that Amazonian manatees are able to fast for up to seven months if necessary.

• GESTATION: The exact gestation period of most manatee species is

not known and is poorly studied. It is known, however, that a Florida manatee's gestation is approximately 12 months.

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Order Sirenia

FAST FACTS ON MANATEES:

• SEXUAL MATURITY: Male manatees (bulls) are sexually mature by about nine to ten years, although some have produced viable sperm at two to three years of age. Female manatees (cows) are sexually mature as young as three years of age.

• LIFE SPAN: No data

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Order Sirenia FAST FACTS ON MANATEES: • RANGE: All living manatee species are found in warm tropical and

subtropical waters. The West Indian manatee was once abundant throughout the tropic and subtropical western North and South Atlantic and Caribbean waters. However, the manatee's numbers have been greatly reduced and is rarely seen throughout its range. The range of the Florida manatee is primarily peninsular Florida but extends as far north as Rhode Island. Manatees have been rescued near Houston, Texas, and Mississippi.

• Antillean manatees have a patchy distribution throughout the Caribbean, Mexico, and northeastern South America. The southern range extends through Central and South America to Brazil.

• West African manatees range from Senegal to Angola, on the west coast of Africa.

• Amazonian manatees are the only species of manatee confined to fresh water. They inhabit the Amazon Basin, mostly in Brazil. They are uncommon or close to extinction in Peru, Ecuador, and Colombia.

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Order Sirenia FAST FACTS ON MANATEES: • HABITAT: The West Indian and West African manatees inhabit

rivers, bays, canals, estuaries, and coastal areas rich in seagrass and other vegetation. They can live in fresh, saline (salt), and brackish waters.

• West Indian manatees may be found in any waterway over 1 m (3.25 ft.) deep and connected to the coast. They prefer waters with temperatures above 21°C (70°F).

• West African manatees live in quiet coastal areas, large rivers, lagoons, and connected lakes, where the water temperature is above 18°C (64°F).

• The Amazonian manatee is restricted to fresh water. They are most common in floodplain lakes and channels in white-water river systems with water temperatures ranging from 25°-30°C (77°-86°F).

• The patchy distribution of manatees throughout all their ranges is due to their search of suitable habitat: plentiful aquatic plants and a freshwater source of water to drink.

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Order Cetacea

• This order includes whales, dolphins and porpoises.

• Fore limbs are modified into flippers.

• Fin-like tail is known as a fluke.

• Nostrils are located on the top of the head as a single or double opening known as a blowhole.

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Order Cetacea

• Within the cetacea, two suborders exist, toothed whales (Odontocetes) and baleen whales (Mysticetes).

• Visually, the two suborders can be easily distinguished by the presence of teeth and a single blowhole (Odontocetes) or baleen and two blowholes.

• SIZE: In general, baleen whales are much larger than toothed whales, ranging in length from about 6.4-27 m (21-85 ft.). Most toothed whales are less than 6.1 m (20 ft.) long.

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Baleen whales have rows of flexible, fibrous plates known as baleen that hang from the upper jaws (seen in diagram below).

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Order Cetacea • Baleen whales are filter feeders. They take in

huge mouthfuls of water containing small fishes or invertebrates. The baleen traps the prey, and water is forced back out of the mouth.

• Baleen whales are represented by 13 species, including the right whale, gray whale, blue whale, and humpback whale.

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Examples of Baleen Whales

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Whales may be identified from their fluke shape, blow pattern or side view during a dive (as shown below).

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Order Cetacea

• Toothed whales are named for their simple, peg-like teeth, which vary considerably in number and size among the species. The teeth of dolphins are conical and interlocking, while those of porpoises are spade-shaped. River dolphins have numerous teeth; most beaked whales have only one or two visible pairs. Teeth are adapted for grasping and tearing, rather than chewing.

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Order Cetacea

• Toothed whales include dolphins, porpoises, belugas, narwhals, sperm whales, killer whales, river dolphins, and beaked whales.

• Depending on the species, toothed whales may be found in coastal waters, rivers or in the pelagic environment.

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Adaptations for Diving: • Rapid breathing prior to dive -known as

apneustic breathing

• Lungs remove 90% of O2 from air (as opposed to 20% for humans)

• Elastic tissue in lungs helps them expand the lungs temporarily during apneustic breathing

• Marine mammals have more blood than non-diving mammals for their size (means more hemoglobin to carry oxygen)

• Muscles contain more myoglobin to hold oxygen in tissues

• The heart rate slows dramatically during a dive – known as bradycardia

• Blood flow is reduced to extremities and digestive system

• Muscles employ anaerobic respiration as necessary (results in lactic acid build-up)

• Marine mammals can tolerate more lactic acid than other mammals

• Rib cage and lungs collapse during dive to force air into tissues and prevent decompression sickness

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Echolocation • Sound waves are emitted as a series of clicks of varying frequencies

• Melon directs the outgoing sound waves

• After the echo strikes an object, it is reflected back

• These reflected echoes are received back by the melon and lower jaw

• The longer it takes a echo to return, the farther away the object is located

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Marine Mammal Behaviors

• Marine mammals as well known for their vocalizations such as the “barking” of sea lions and songs of the humpback whale.

• Marine mammals engage in play activities regularly including sexual play.

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Marine Mammal Behaviors

• Many species of marine mammals are known to jump out of the water and crash back into the water on their backs. This is known as breaching.

• The reasons for this behavior may be removing parasites, a warning signal, to avoid suitors or to have fun!

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Marine Mammal Behaviors

• Marine mammals sometimes hold their bodies out of the water. This behavior is known as “spyhopping.”

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Marine Mammal Behaviors

• Many marine mammals are known for their long migrations.

• The longest migration is that of the gray whale; this migration is over 11,000 miles!!

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Notable Migrations

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Marine Mammal Behaviors

Care giving and Strandings:

• When one member of a group (pod) of animals is sick/injured, other members will care for it. Mass strandings are often the result of caregivers following a sick/injured animal to shore.

• As an example, 58 pilot whales mass stranded in July, 2002 at Chapin Beach. Volunteers desperately tried to protect the animals from the summer heat with sheets and water, but unfortunately the elements proved too extreme for the whales.

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Watch this video of a stranded Killer Whale rescue.

• Click to watch the rescue video

Reproduction in Marine Mammals

• Fertilization is internal via copulation

• Copulation occurs on land for pinnipeds where males compete for “harems”

• Other marine mammals copulate at sea

• Sexual play is common in marine mammals

• Some marine mammals use delayed implantation of the fetus – this allows the calf to be born at a time that is best for the survival of the calf

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Reproduction in Marine Mammals

• Gestation time varies in marine mammals; normally 11-12 months in cetaceans.

• Calves are born tail first so that they can remain attached to the placenta until the entire body is out and the animal can be forced to the water’s surface to take its first breath.

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