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MARINE MAMMALS PLAY A PIVOTAL ROLE IN MAINTAINING THE ECOLOGICAL EQUILIBRIUM OF THE OCEANS BY CONTRIBUTING TO NUTRIENT CYCLING AND SERVING AS CRUCIAL INDICATORS OF OVERALL MARINE ECOSYSTEM HEALTH.
Marine mammals belong to the Animalia kingdom, Chordata phylum, and Mammalia class. They encompass 129 living species categorized into three orders: Cetartiodactyla, which includes cetaceans (whales, dolphins, and porpoises); Carnivora, covering pinnipeds (walruses, sea lions, and seals), sea otters, and polar bears; and Sirenia, which includes sea cows (now extinct), manatees, and dugongs. Among these groups, cetaceans, pinnipeds, and sirenians are considered the most ancient marine mammal orders. In contrast, sea otters and polar bears are relatively recent additions, with polar bears even capable of hybridizing with their terrestrial relatives.
These captivating creatures have developed remarkable physical adaptations that enable them to thrive in the demanding marine environment, marked by extreme temperatures, depths, pressure, and darkness.
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Sirenia_Dugong (Dugong Dugon)
photo source: Canva.com
CETACEANS PLAY A VITAL ROLE IN MAINTAINING MARINE ECOSYSTEMS' HEALTH AND BALANCE BY REGULATING PREY POPULATIONS, PROMOTING NUTRIENT CYCLING AND CONTRIBUTING CARBON SEQUESTRATION.
The largest group of marine mammals is Cetacea, comprising around 90 species, divided into two main subgroups: mysticetes and odontocetes.
Mysticetes (whales, minke whales, humpback whales), or baleen whales, lack teeth but instead possess baleen plates they use to filter and capture small prey from the water.
Odontocetes (dolphins, porpoises, narwhals, belugas, sperm whales and killer whales), also known as toothed whales, are characterized by their possession of teeth and their ability to utilize echolocation for hunting and navigation.
WHALES ARE MAGNIFICENT MARINE MAMMALS KNOWN FOR THEIR IMMENSE SIZE AND INCREDIBLE MIGRATIONS ACROSS THE WORLD'S OCEANS.
Whales comprise more than 90 distinct species and are found in oceans around the world, from the Arctic and Antarctic regions to tropical waters. They are highly adapted to life in the water, with streamlined bodies, powerful tails, and the ability to hold their breath for extended periods.
Blue Whale (Balaenoptera musculus) is the largest animal on Earth.
These magnificent creatures can grow to lengths of over 30 meters weigh up to 200 tonnes and survive by consuming some of the smallest creatures in the ocean called krill, which they filter through baleen plates in their mouths.
WHALES PLAY VITAL ROLES IN MARINE ECOSYSTEMS DUE TO THEIR SIGNIFICANT IMPACT ON THE FOOD WEB.
Whales are recognized as "ecosystem engineers" because of their ability to trigger trophic cascades.
Whales excrete substantial amounts of nutrient-rich faecal plumes into the water by consuming large quantities of zooplankton, particularly krill, which they filter through their baleen. These plumes contain mineral salts and iron, acting as fertilizers that promote the growth of phytoplankton, the foundation of the marine food chain.
Whale feces
photo credit: Tethys ONLUS
The vertical movement of whales, as they navigate between deep water and the surface, creates a significant stirring effect that enhances phytoplankton productivity. Furthermore, the seasonal migration of many whale species facilitates the horizontal transport of nutrients from one location to another.
Consequently, an increased whale population leads to elevated fertilization levels, enhanced phytoplankton growth, increased oxygen production, and reduced carbon dioxide levels in the marine environment. Moreover, whales absorb carbon during their lifetime and, upon death, sink to the ocean floor, taking carbon with them into the deep sea. Some calculations suggest that if whales were as numerous as they were before the industrial hunting that depleted their populations, around 4-5 million individuals, approximately 160,000 tonnes of carbon, could be sequestered at the bottom of the sea.
WHALES ARE KNOWN FOR THEIR BEAUTIFUL SONGS WHICH SERVE AS A TESTAMENT TO THE REMARKABLE COMMUNICATION SKILLS OF THESE MAJESTIC CREATURES.
Whales use a variety of vocalizations, including songs, clicks, and whistles, to communicate with other members of their pod or group. These vocalizations serve vital functions in navigation, hunting, and social interactions.
For example, during the enchanting time of the breeding season, certain whale species engage in a mesmerizing courtship ritual known as "whale courtship display" or "whale mating behaviour. It is a fascinating phenomenon observed in certain whale species during the breeding season. It involves coordinated movements, vocalizations, and displays performed by males to attract females.
Humpback whales are famous for their acrobatic breaching and intricate songs, while blue whales use low-frequency vocalizations. This courtship behaviour is crucial for reproduction, but it faces threats from human activities, such as noise pollution from shipping traffic, which can disrupt this dance.
Many species of whales, such as killer whales (orcas) and pilot whales, indeed form tightly-knit family groups known as pods. These pods are essential for their survival and social well-being, and they exhibit complex social structures and behaviours.
A group of killer whales attempt to dislodge a crabeater seal on an ice floe
photo credit: Callan Carpenter
Killer whales, or orcas, are part of the Odontocete family.
They live in matrilineal groups, which means that multiple generations of females, including mothers, daughters, and grandmothers, stay together in the same pod. Male orcas typically remain with their natal pod throughout their lives, forming strong bonds with their female relatives.
Killer whales collaborate for hunting, and their diet includes fish, squid, seals, and sea lions. This diverse diet allows them to regulate prey populations, preventing overconsumption. Their predation control sets off a trophic cascade, which ensures the overall health of the marine food chain.
Long-finned pilot whales (Globicephala melas)
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Pilot whales, members of the Delphinidae family, encompass two primary species: the long-finned pilot whale (Globicephala melas) and the short-finned pilot whale (Globicephala macrorhynchus). They have robust bodies, small dorsal fins, and dark colouration with distinctive facial patches. Pilot whales are distributed globally in oceans, with specific habitat preferences depending on the species.
These marine mammals exhibit intricate social structures within matrilineal pods, communicate through vocalizations, and engage in cooperative hunting. Their diet comprises squid, fish, and occasional cetaceans.
A pod of dolphins in sardine run in South Africa
video source: Canva.com
Dolphins, comprising approximately 40 species, are remarkable marine mammals recognized for their sleek and hydrodynamic bodies. They sport a distinctive dorsal fin on their backs, which aids in maintaining stability, as well as pectoral fins that serve as agile appendages for steering and manoeuvring gracefully through the water.
These highly sociable creatures often form cohesive groups known as pods, varying in size from just a few individuals to several hundred. Dolphins establish strong social bonds and engage in cooperative activities such as playful interactions and collaborative hunting strategies. These hunting techniques, referred to as "fish-kicking" or "fish-whacking," are designed to enhance their success in capturing prey efficiently. Their diet can vary depending on their habitat and prey availability, but they typically consume significant quantities of fish like herring, mackerel, sardines, and squids. Consequently, they occupy a critical position in the marine food chain as apex predators, playing a vital role in maintaining the equilibrium of marine ecosystems.
Amazon river dolphin (Inia geoffrensis)
photo source: Canva.com
The Amazon River Dolphin (Inia geoffrensis), commonly referred to as the Boto or Pink Dolphin, is a fascinating species that inhabits the freshwater rivers and tributaries of the Amazon Basin in South America. It is the largest species of river dolphin in the world and is renowned for its distinctive pink colouration and unique adaptations to its aquatic environment.
CETACEANS FACE NUMEROUS THREATS IN THEIR NATURAL HABITATS, JEOPARDIZING THEIR SURVIVAL AND WELL-BEING.
A major concern is the loss and degradation of habitat that marine mammals face due to pollution, climate change and coastal development. These factors alter their feeding, reproduction and migration patterns, leading to population decline. In addition, entanglement in fishing gear and collisions with boats can cause injuries, hinder movement and even result in death.
Human activities, such as the use of naval sonar and seismic exploration, generate high-intensity underwater noise that can disrupt the communication, navigation and feeding patterns of marine mammals.
In addition, the depletion of prey species due to overfishing can lead to food shortages for marine mammals, affecting their overall health and reproduction rates.
Another critical problem is the illegal hunting of some marine mammals for their meat, fat and other body parts, which pushes some populations towards extinction.
Illustration on noise pollution
image credit: NOAA Fisheries
In the Faroe Islands, an autonomous territory of Denmark, there exists a contentious tradition known as the "grindadráp" or "grind." This practice involves organized hunts conducted by local communities, where whales or dolphins are herded towards a shallow bay or designated killing beach using boats and human chains. Once corralled, locals enter the water and dispatch the animals with traditional tools like knives or lances. The resulting meat and blubber are distributed within the community. Notably, the Faroe Islands have a strong fishing industry, with around 90% of their exports being fisheries-related.
These are Atlantic White-sided Dolphins, on a concrete-floored dock at a small port called Hvalba, which is in the Faeroe Islands, located between the UK and Iceland
image credit: Erik Christensen
However, the grindadráp has come under intense scrutiny from animal rights organizations, sparking debates about its sustainability and ethical implications in the modern world. The International Whaling Commission initiated a Whaling Moratorium in 1982, which halted commercial whaling in most countries. Nevertheless, Norway, Japan, and Iceland objected to this moratorium and continued their whaling activities. Among these nations, Norway holds the distinction of being the world's largest whaling country.
It's important to distinguish between the Faroe Islands' grindadráp, which is conducted on a smaller scale primarily for local consumption, and commercial whaling operations in Norway, Japan, and Iceland, which export whale products. Controversy persists over these practices, with debates centring on conservation, animal welfare, and cultural traditions.
PINNIPEDS WELL-ADAPTED TO BOTH AQUATIC AND TERRESTRIAL ENVIRONMENTS PLAY A PIVOTAL ROLE IN MARINE FOOD WEBS BY REGULATING PREY POPULATIONS AND INFLUENCING THE HEALTH AND ABUNDANCE OF VARIOUS MARINE SPECIES.
Pinnipeds are marine mammals in the order Carnivora, known for their agility and speed underwater. However, despite their aquatic adaptations, they often appear somewhat ungainly on land.
These fascinating creatures inhabit various regions across the globe, including both colder and warmer waters, such as the Mediterranean and North Sea.
Seal hunting
video source: Canva.com
Pinnipeds hold a significant ecological role as indicator species, serving as crucial barometers of the overall health of marine ecosystems. Monitoring their population's health and behaviour yields valuable insights into the well-being of these environments, allowing for early detection of changes in factors like food availability and water quality. Additionally, pinnipeds occupy pivotal positions in marine food webs, fulfilling dual roles as both predators and prey. Their activities play a pivotal role in regulating the populations of other marine species, such as fish and cephalopods, thereby contributing significantly to the balance and stability of marine ecosystems.
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Harbor seals (Phoca vitulina) on ice
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Seals are the largest subgroup of pinnipeds and are divided into two main families: true seals and eared seals.
True seals (Phocidae), like harbour and elephant seals, lack external ear flaps and have shorter front flippers.
In contrast, eared seals (Otariidae), which include sea lions and fur seals, have visible ear flaps and longer front flippers, making them more efficient at navigating on land.
Elephant seal (Mirounga)
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Brown fur seal ( Arctocephalus pusillus)
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Australian sea lions (Neophoca cinerea)
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The walrus is a large marine mammal known for its distinctive features, including long tusks and whiskers, which help it navigate and locate prey in the sea. The tusks serve various purposes such as establishing dominance during the breeding season, defence against predators, hauling their bodies out of the water, and foraging. They are particularly useful in breaking through ice barriers and creating breathing holes.
Walruses gather in large numbers on land or ice during the summer months in what is called a haulout. These gatherings provide a place for walruses to rest, socialize, moult, and give birth. However, the loss of sea ice and reduction in suitable habitats have had a detrimental impact on walruses.
Due to the increasing distances between foraging areas and haulout sites, walruses are forced to undertake longer and more strenuous journeys. This situation can lead to exhaustion, heightened predation risks, and reduced reproductive success.
Walrus (Odobenus rosmarus)
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Congregation of walruses
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SIRENIANS ARE ESSENTIAL TO THE OCEAN'S ECOSYSTEMS, ACTING AS ECOSYSTEM ENGINEERS BY GRAZING ON MACROALGAE AND HENCE KEEPING THEIR POPULATION IN BALANCE, AVOIDING EXCESSIVE GROWTH.
Sirenians, often commonly referred to as sea cows, are indeed captivating marine mammals that include two primary species: manatees and dugongs. These magnificent creatures possess notable characteristics such as large bodies, paddle-shaped flippers, and tails adapted into fluke-like structures.
These adaptations enable them to thrive in their underwater environments.
Manatee ( Trichechus)
video source: Canva.com
Manatees predominantly inhabit the waters of the Americas, from the warm coastal regions of the southeastern United States to the lush river systems of Central and South America.
Dugongs, on the other hand, are primarily found in the Indo-Pacific region, with their range extending from the eastern coast of Africa to the waters of Southeast Asia and northern Australia.
Dugong (Dugong Dugon) eating seagrass
photo source: Canva.com
One of the most noteworthy aspects of mermaids is their role as herbivores and their critical impact on the conservation of seagrass ecosystems. These gentle giants are expert grazers and feed on seagrass beds in shallow coastal areas and estuaries. By consuming seagrasses, they play a key role in controlling their growth, preventing them from becoming too dense and promoting healthier seagrass meadows.
SEA OTTERS, SMALL MARINE MAMMALS, SERVE AS KEYSTONE SPECIES IN MARINE ECOSYSTEMS BY REGULATING SEA URCHIN POPULATIONS, PREVENTING UNCHECKED GRAZING ON KELP FORESTS, AND AVERTING A CASCADE OF DETRIMENTAL EFFECTS THROUGHOUT THE COASTAL ECOSYSTEM.
Belonging to the Mustelidae family, commonly known as the weasel family, sea otters possess the densest fur of any known animal, with an astonishing 600,000 to 1,000,000 hairs per square inch. This fur acts as essential insulation against the frigid ocean waters. Adult sea otters typically measure between 3 to 4 feet (0.9 to 1.2 meters) in length and can weigh anywhere from 30 to 100 pounds (14 to 45 kilograms), with males generally larger than females.
Sea otters (Enhydra lutris)
photo source: Canva.com
Sea otters are renowned for their playful and sociable nature. They are frequently observed floating on their backs at the water's surface, using their stomachs as an impromptu table for grooming their fur and eating.
Highly skilled at opening and consuming their food, sea otters are carnivores and primarily eat a diet based on fish, crustaceans, molluscs, and invertebrates such as sea urchins, octopuses, and echinoderms.
Through their consumption of sea urchins, sea otters play a vital role in controlling the population of these herbivores, preventing overgrazing of kelp forests. These healthy kelp forests, in turn, provide a vital habitat and a source of sustenance for numerous other marine species.
Polar bear eating seal on pack ice
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A Sea otter (Enhydra lutris) eating a mollusc
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POLAR BEARS ARE MARINE MAMMALS DUE TO THEIR RELIANCE ON SEA ICE AS A PLATFORM FOR HUNTING SEALS, THEIR PRIMARY PRAY, AND THEIR EXCEPTIONAL SWIMMING ABILITIES IN THE ICY WATERS OF THE ARCTIC.
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Polar bear (Ursus maritimus)
photo source: Canva.com
Polar bears have evolved with unique adaptations for a semi-aquatic lifestyle. They spend a significant portion of their lives on sea ice, where they rely on seals - particularly ringed and bearded seals- as their primary food source. Despite seals seeking refuge beneath the icy surface of the Arctic waters in their breathing holes, polar bears' exceptional hunting skills make them formidable predators. As a result, they are undisputedly at the top of the Arctic food chain.
A Polar bear eating seal on pack ice
photo source: Canva.com
The skin of a polar bear is black, not white, allowing it to absorb heat from the sun and stay warm in the Arctic. This skin can be up to 4.5 centimetres (1.8 inches) thick in certain areas, providing insulation against cold water and freezing temperatures. Together with this thickness, polar bears have a substantial layer of blubber underneath their skin, which can reach thicknesses of up to 10 centimetres (4 inches).
This blubber layer is essential for both insulation and energy storage, enabling their survival in the challenging Arctic environment.
Polar bear fur
photo source: Canva.com
Polar bear underwater
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POLAR BEARS ARE CURRENTLY FACING SIGNIFICANT THREATS TO THEIR SURVIVAL DUE TO CLIMATE CHANGE.
Polar bears on ice
photo source: Canva.com
Climate change has led to a significant reduction in Arctic sea ice, causing it to melt earlier in the spring and freeze later in the fall. This abbreviated ice season has profound consequences for polar bears, which heavily depend on ice platforms for hunting seals, their primary source of sustenance.
The shortened hunting season compels polar bears to undertake lengthier swims in search of seals, a physically demanding endeavour that can lead to exhaustion and, tragically, even drowning. Furthermore, the decreased ice cover makes it more challenging for polar bears to locate seal breathing holes, further hindering their ability to hunt effectively. This situation results in widespread exhaustion, malnutrition, and a detrimental impact on their health and reproductive capacities. Malnourished mother polar bears have a reduced likelihood of successfully raising their cubs, leading to diminished survival rates.
As a desperate survival tactic, the food scarcity in the evolving Arctic environment has driven some polar bears to engage in cannibalism. Starving bears may resort to attacking and consuming other bears, including cubs, underscoring the severity of the food shortage issue.
Polar bear (Ursus maritimus) on ice
photo source: Canva.com
These challenges faced by polar bears have far-reaching consequences for the entire Arctic ecosystem. The diminishing sea ice disrupts the delicate balance of the Arctic food web, affecting not only polar bears, but also seals, fish, and other Arctic species.
Polar bear (Ursus maritimus)
photo source: Canva.com
