The Giants

Many people have a passion for the sea, but only a few are really aware of what is happening under its surface. 

The big marine animals are the seas most emblematic spices. They are appealing symbols for the public and they top the food web, thus reflecting the health of the marine ecosystem. We have selected the “big five” of the oceans so that through remarkable, surprising and sometimes shocking stories featuring these well-known ‘Giants’, we hope to raise more awareness and help educate, inspire and motivate positive change.

They will help to understand how complex problematic such as ocean acidification, climate change, plastic pollution or overfishing affect the equilibrium of this fragile environment the marine animals (and we) depend on.

Sharks

The earliest known sharks date from more than 420 million years ago. Since that time, sharks have diversified into 440 species. They range in size from the small dwarf lanternshark, a deep sea species of only 17 centimeters in length, to the whale shark, the largest fish in the world, which reaches approximately 12 meters. Despite its size, the whale shark feeds only on plankton, squid, and small fish by filter feeding. Well-known species such as the great white shark, tiger shark, blue shark, mako shark, and the hammerhead shark are apex predators – organisms at the top of their underwater food chain. Their predatory skill fascinates and frightens humans, even though their survival is threatened by human-related activities.

It is estimated that 100 million sharks are killed by people every year, due to commercial and recreational fishing. Sharks are a common seafood in many places, including Japan and Australia. They are often killed for shark fin soup. Fishermen capture live sharks, fin them, and dump the finless animal back into the water which soon dies from suffocation or predators. Shark fin has become a major trade within black markets all over the world.

Sharks generally reach sexual maturity only after many years and produce few offspring in comparison to other fish. Major declines in shark stocks have been recorded—some species have been depleted by over 90% over the past 20–30 years. If these top predators disappear, it is the entire equilibrium of the marine ecosystem which is threatened.

Cetaceans

Cetaceans  include the marine mammals commonly known as whales, dolphins, and porpoises. They range in size from Commerson’s dolphin, smaller than a human, to the Blue Whale, the largest animal ever known to have lived, reaching over 30 metres in length and 180 tons. Cetaceans are adapted to aquatic life, their forelimbs being modified into flippers and they can remain under water for extended periods without breathing. Some species such as Killer Whale are noted for their high intelligence. The toothed whales such as the sperm whale, beluga, dolphins and porpoises, have teeth that they use for catching fish, squid or other marine life. Other cetaceans such as the Humpback, Bowhead and Minke whales instead have baleen plates which filter small animals (such as krill and fish) from the seawater.

Turtles

Sea turtles became distinct from all other terrestrial turtles at least 110 million years ago. They can be found in all oceans except for the Polar Regions. The leatherback is the largest sea turtle, measuring up to  2.1 meter in length at maturity and weighing up to 590 kg.

Sea turtles live up to 80 years and it takes them decades to reach sexual maturity. After mating at sea, the adult female sea turtles return to land to create a nest and lay up to 250 eggs. It then returns to the ocean, leaving the eggs untended. The hatchling’s gender depends on the sand temperature.

Sea turtles act as grazing animals that cut the grass short and help maintain the health of the sea grass beds. Sea grass beds provide breeding and developmental grounds for numerous species of fish, shellfish and crustaceans.

Marine sea turtles are caught worldwide, although it is illegal to hunt most species in many countries. A great deal of intentional marine sea turtle harvests are for food. There is also black-market demand for tortoiseshell for both decoration and supposed health benefits.  One of the most significant threats now comes from by catch due to imprecise fishing methods.

All 7 species of sea turtles are listed as threatened or endangered. The leatherback, Kemp’s Ridley, and hawksbill sea turtles are critically endangered. The Olive Ridley and green sea turtles are endangered, and the loggerhead is threatened. The flatback’s conservation status is unclear due to lack of data.

Pelagic Fish

Pelagic fish live near the surface or in the water column of coastal and ocean waters. They range in size from small coastal forage fish, such as herrings and sardines, to large apex predator oceanic fishes, such as the atlantic bluefin tuna or  swordfish who commonly reach 3 m in length, and up to 650 kg

Pelagic fish are usually agile swimmers with streamlined bodies, capable of sustained cruising on long distance The Indo-Pacific sailfish can sprint at over 110 kilometers per hour. Some tuna species cruise across the Pacific Ocean. Many pelagic fish swim in schools weighing hundreds of tonnes. Others are solitary, like the large ocean sunfish weighing over 500 kilograms, which sometimes drift passively with ocean currents, eating jellyfish.

Tuna in particular are of major importance to commercial fisheries. Other large pelagic fish are premier game fish, particularly marlin and swordfish.

The Atlantic bluefin tuna has been the foundation of one of the world’s most lucrative commercial fisheries. Medium-sized and large individuals are heavily targeted for the Japanese raw fish market, where all bluefin species are highly prized for sushi and sashimi. This commercial importance has led to severe overfishing. The Atlantic population has declined by nearly 90 percent since the 1970s

Other Marine Mammals

Marine mammals rely on the ocean for their existence. While their number is small compared to those found on land they play important roles in maintaining marine ecosystems, especially through regulation of prey populations. Sea lions have an average life span of 20–30 years. The largest can weigh up to 1000 kg. Manatees weight 400 to 550 kilograms, measure 3.0 meters and live up to 60 years. Half a manatee’s day is spent sleeping in the water, surfacing for air regularly. It spends most of the rest of the time grazing in shallow waters

Marine mammals were hunted by coastal aboriginal humans historically for food and other resources. The effects of this were only localized as hunting efforts were on a relatively small scale. Later, commercial hunting was developed and marine mammals were heavily exploited. This led for instance to the extinction of the Steller’s Sea Cow and the Caribbean monk seal. Today Habitat degradation is an important threat for these animals. It is caused by a number of human activities and marine mammals that live in coastal environments are most likely to be affected by it. For example, extensive shellfish aquaculture takes up valuable space used by coastal marine mammals for important activities such as breeding, foraging and resting.

The fishery industry not only threatens marine mammals through by-catch, but also through competition for food. Large scale fisheries have led to the depletion of fish stocks that are important prey species for marine mammals. As the fish stocks have been depleted, the competition between marine mammals and fisheries has sometimes led to conflict. Large-scale culling of populations of marine mammals by commercial fishers has been initiated in a number of areas in order to protect fish stocks for human consumption.

Contaminants such as mercury and lead that are discharged into the marine environment accumulate in the bodies of marine mammals. They can impair the reproductive system. Other pollutants such as oil, plastic debris and sewage threaten the livelihood of marine mammals.