HABITAT

Marine mammals are found in all the world’s oceans and seas. Each species is adapted to live in its surrounding environment.

A place that offers a certain set of stable living conditions to plants and animals is called a habitat.
In Greece there are many different kinds of habitats and each kind hosts different species of marine mammals.

Sea caves are caves that are accessible from the sea and are an ideal refuge for monk seals. Hundreds of remote sea caves in Greece are used by female monk seals, who need privacy and protection from bad weather conditions in order to give birth and nurse their young. Their pups are left alone in the cave from time to time so that the mother can go to hunt for food.

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The names «φωκοσπηλιά» (seal cave) or «φωκιότρυπα» (seal hole) are given to many sea caves in Greece where seals are known to inhabit.

Many marine mammals live close to the coast (eg. Bottlenose dolphin, Harbour porpoises, seals) or in enclosed bays (eg. Common dolphin, Striped dolphin) such as the Gulf of Amvrakikos, Cornith and Pagasetic.

 

These habitats are characterized by nutrient-rich waters, mild conditions (a lot of light in the water, warm water), but high levels of human activity, unfortunately, affect these mammals.
Most marine mammals live in the open sea, away from the coast. On the surface there is plenty of oxygen and light and the plankton that grows there is a major food source for whales. All marine mammals come to the surface to breathe before diving to greater depths in search of food.

 

Light decreases with increasing depth in the sea. Sunlight cannot reach beyond depths of 200 meters, so animals that hunt there are adapted to live and hunt in the dark.
In many parts in the Greek seas, the water is very deep (eg southwest of Pylos in Peloponnese, where the deepest point of the Mediterranean basin, at 5.125 meters deep is found, and southwest of Crete and southeast of Rhodes island). Even in that completely dark and deep environment there is abundant food for some marine mammals. The abyssal depths are a suitable habitat for Sperm whales and Cuvier’s beaked whales to hunt for giant squid.

MIGRATION

Whales and seals live mainly in the seas and oceans, making large migrations to find food or to go to suitable areas for breeding.

These animals can travel thousand kilometers in a few months and at specific periods in the year. During migration, they usually do not feed and survive largely off the fat deposits they have accumulated in their blubber.

But how do these marine mammals find their way during their migrations?

In cetaceans, studies focused in mapping their movements, have showed that the animals move according to the earth’s magnetic field as well as by sounds they emit.

We know that marine mammals perceive Earth’s magnetic field with the help of a biomagnet, in other words, an internal biological compass.

They can also navigate by the use of sound. Cetaceans emit sounds that, when reflected back to them give them messages and information so that they can precisely perceive their surrounding environment. This ability, along with their developed memory, helps them recognize routes and topographic information during their journey.

Some marine mammals that migrate regularly are the fin whale, the sperm whale, and the humpback whale. However, fin whales and sperm whales that live in the Mediterranean, do not immigrate out of it.

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HUNTING & NUTRITION

Surprisingly, the largest animals in the world, whales, feed on some of the smallest, such as zooplankton, krill (really tiny shrimp), and small fish. They open their mouths very wide in order to fill it with big amounts of zooplankton, as well as enormous volumes of seawater. They then use their baleens to filter their tiny food and expel only the water.

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Although the size of their prey is very small, they eat enormous quantities of food. Blue whales, the largest animal to ever live on earth, consume approximately 4.000 kilograms of zooplankton per day!

Other marine mammals, like sperm whales and Cuvier’s beaked whales, feed primarily on giant squid. To find their food, they must dive to enormous depths. When they locate prey, they approach and bite, immobilizing the squid before they swallow it whole without chewing. These squid, because sometimes they are very large (1-1.5 meters), fight hard against the whales and many times injure them with their beaks and the suction cups on their tentacles.

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Dolphins, seals and porpoises have a diversified diet. They feed on cephalopods (octopus, squid, cuttlefish) as well as fish like breams, snapper, bogue, smelt, etc

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They catch their prey with their teeth and swallow it whole. They can travel many miles in search of food. Marine mammals prefer fish that are also fished and eaten by humans, which, unfortunately, makes them unpopular to fishermen, who often see marine mammals as competition and therefore sometimes hunt them. The latter practices are certainly harmful for the natural marine environment, since the marine mammals that constitute necessary elements of the marine ecosystems. The greatest threats to marine ecosystems unfortunately are caused mainly from human activities (over fishing and illegal fishing, pollution).

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REPRODUCTION

Cetaceans, like all mammals, carry their young in the mother’s uterus for a period of 9-18 months. They are viviparous animals, giving birth to young that were fed with a placenta, not developed in eggs.

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Their pups are born tail-first to prevent drowning. When the umbilical cord breaks, the mother helps the calve to reach the sea surface and take its first breath. The young can swim immediately after birth.

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Mothers nurse their young for a long period. Their milk is rich in fat and is an ideal food for rapid growth. In most species, the nursing period lasts longer than a year and is important because it creates a strong bond between mother and young.

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Cetaceans give birth to one baby every 1-3 years.

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In general, pinnipeds, mate once every year. They give birth once every 1-2 years, usually to one pup and pregnancy for most species lasts from 9-11 months. Pinnipeds give birth on land.

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From the time they are born until they are weaned, the young are completely dependent on their mothers, who nurse them and teach them to hunt. Once weaned, the young must survive on their own and hunt for their own food.

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SOCIAL RELATIONS

Odontocetes

Out of all the marine mammals, odontocetes seem to create the most stable relations amongst each other. They create small groups (or pods) and, in many cases, members of a pod stay together throughout their lives. They will even stay with sick or injured members, sometimes helping them to swim. They will protect the pod’s young, while the mother leaves for a while to look for food. They mourn the death of young ones. They also teach the young to hunt and even to use sponges as tools.

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Their altruistic behavior is not limited only to their species. There have been reports of dolphins protecting swimmers from sharks by circling them, and dolphins have helped whales find their way back to the sea, when they enter shallow water.

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Whales

Whales are a more solitary species, although the relationship of a mother with her newborn is very close and can last up to 1 year. These animals spend more time alone. Although solitary animals, they seem to be in constant communication with one or more whales of their same species, that may be located several hundred kilometers away. This constant, long-distance communication allows them to alert each other in the case of large quantities of food or danger.

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Pinnipeds

Social ties between pinnipeds are short. The most important bond is between mother and young, which lasts for the duration of nursing. This period is different for each species from 3-4 days, in the case of the hooded seal, and up to 3-4 months in the case of monk seals.
Some species of pinnipeds gather in large groups, called colonies, on coasts, beaches, and even on ice sheets to give birth and raise their young. The seals that live in Greek Seas (Mediterranean monk seal), however, are quite solitary animals and are rarely seen in groups either at sea, on isolated beaches, or especially in sea caves.

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COMMUNICATION

Cetaceans and pinnipeds communicate through body language and by producing sounds. Body language includes high jumps out of the water (like dolphins and whales) and smacking of their tails on the water (sperm whales and whales).

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There is a greater variety in the production of sounds, because the sounds produced are different for each species and unique to each animal!

Pinnipeds can also recognize each other by smell.

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Cetaceans

Whales produce sounds and low-frequency sounds. Humpback whales produce sounds reminiscent of melancholic melodies. The sounds are perceived over very large distances of water and thus they can communicate with each other, even if they are separated by a whole ocean.

Dolphins and other odontocetes produce a wide variety of sounds and high-frequency sounds, resembling whistles, sighs, squeaks, and grunts. They often produce consecutive sounds that are heard as clicks. This communication system is reminiscent of Morse code and is used for echolocation.

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[Low- and high-frequency sounds: They are sounds that humans cannot hear because they are at frequencies that cannot be grasped by the human ear.]

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Pinnipeds

Pinnipeds produce a wide variety of sounds both on land and in water. These sounds resemble whining, grunts, roars and sometimes slow singing. With these sounds, mothers can communicate with their young; males can look for mates or compete with other males, so as to mate with a female.

 

Pinnipeds also recognize each other by smell. Each animal has a unique smell and in combination with sounds, animals can recognize each other. In the colonies of otariids, which consist of thousands of individuals, mothers recognize their pups by smell and sound.

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