The order Cetacea is part of the Kingdom Animalia and Phylum Chordata. This order includes several marine mammals such as dolphins, whales and porpoises. The Cetaceans group consists of some of the largest mammals, both living and extinct. For example, the largest mammal living on Earth is the blue whale (Balaenoptera musculus), which can grow up to a length of 80-100 feet and weighing around 200 tons (World Wildlife Fund, 2018).
The Morphology and Ecology of Cetaceans
Over the course of evolution, cetaceans have developed their limbs into fins or flippers. Their hind limbs are generally absent; however, they have internal vestigial remnants. These marine mammals have a telescoped skull with eyes, ears and a single or a double blow-hole. This blowhole releases a sound, which is produced from the air expelled from the blowhole. They have no vocal apparatus; however, they are able to produce high and low frequency sounds, which are utilised for communication, mating rituals and echolocation. The sounds produced by a cetacean, are specific to each individual, allowing them to communicate and identify one another. A particular characteristic, which is not that commonly found amongst marine organisms, is that these marine mammals, are able to give birth to live young.
Whales, porpoises and dolphins, are mainly pelagic organisms and inhabit open waters, however, they may also live near the coast. They also seasonally migrate, in order to avoid cold temperatures in Winter, where they move to tropical regions to give birth and they migrate back to cooler waters in Summer (Bradley, 1997).
Cetaceans in Bangladesh
In Bangladesh, cetaceans can be found in rivers, however the locals are not well informed on these marine mammals. For example, dolphins can be seen swimming through the Ganges, Padma, Jamuna, Sangu, Meghna and the Karnaphuli rivers. Other cetaceans, such as the Irrwaddy Dolphins live along the coast and in estuaries and Porpoises and Indo-Pacific humpback dolphins inhabit mangrove forests. Spinner dolphins, Dan Tropical Spotted Dolphins and Omdo-Pacific Bottlenose Dolphins are all categorised as “endangered” and can be seen roaming throughout the seas in Bangladesh (Bangladesh Channel Information, 2018). Whales have also been spotted in several coastal zones throughout Bangladesh.
Threats faced by Cetaceans
Cetaceans faced and still face numerous threats. The latter include:
Whaling, which is an issue that needs to be stopped, since whaling industries have killed off species after species.
Climate change, which is having a huge effect on sea temperature, resulting in a decrease in krill populations, therefore decreasing the natural food supply for cetaceans.
Fishing activities, which results in a number of cetaceans to be caught as by-catch during fishing activities.
Pollution, such as toxic contamination.
Degradation of the habitat.
Ship striking.
(World Wildlife Fund, 2017)
Protection of Cetaceans in Bangladesh
The Wildlife Conservation Society (WCS) aided the Bengali government to establish 3 mangrove forest sanctuaries, to conserve the last 2 freshwater dolphins and the Bryde’s whale population. In 2014, the WCS aided in the implementation of the first Marine Protected Area (MPA) in Bangladesh. The main aim of this MPA is to protect cetaceans and other marine species inhabiting this 1700 square kilometre region (Wildlife Conservation Society, 2018).
The MPA formed in 2014, is called the “Swatch of No Ground Marine Protected Area” (SoNG MPA) and this was implemented by the Ministry of Environment and Forest. This MPA has a maximum depth of over 900m. It borders with Indian waters and therefore the formation of this MPA promoted several discussions between Bangladesh and India, in order to safeguard these species. The SOS project was also a major component in the formation of this SoNG MPA, as it collaborated with fishers carrying out the gillnet fishery, in order to save these threatened marine mammals from gillnet fishing gear (IUCN, 2014).
Bonus Fact: Cetacean Stranding
Cetacean stranding has been occurring, since when human communities started living close to the coast. The reasons for this phenomenon are unknown, however it is presumed to be a natural one. A cetacean that strands itself, is generally in poor health, injured or dead. However, healthy cetaceans have been stranded on the shore but are not able to return to the water and may undergo stress. If a whole pod of cetaceans is beached or stranded and some cetaceans manage to return to the water, these organisms may return and strand themselves, due to their instinctive and strong desire to stay with their pod. It is assumed that these strandings, occur due to changes in currents, earthquakes, climate change or infections of the inner ear, which can result in disorientation (Beckman, 2013).
References:
Bangladesh Channel Information (2018) Introducing the Whales and Dolphins of Bangladesh [online], Available at: http://www.bangladesh.com/blog/introducing-the-whales-and-dolphins-of-bangladesh, (Accessed on: 25/11/18).
Beckman, D.W. (2013) Marine Environmental Biology and Conservation [online], Available at: https://books.google.com.mt/books?id=vW3pbgIcnXAC&pg=PA336&dq=cetacea+definition+marine+biology&hl=mt&sa=X&ved=0ahUKEwjBxaeut-_eAhUJ_SoKHd1BBMIQ6AEITDAF#v=onepage&q=cetacea%20definition%20marine%20biology&f=false, (Accessed on: 25/11/18).
Bradley, L. (1997) The Mammals of Texas-Online Edition [online], Available at: http://www.nsrl.ttu.edu/tmot1/ordcetac.htm, (Accessed on: 25/11/18).
IUCN (2018) Bangladesh creates new Marine Protected Area for Dolphins, Whales, Sharks and Turtles [online], Available at: https://www.iucn.org/content/bangladesh-creates-new-marine-protected-area-dolphins-whales-sharks-and-turtles, (Accessed on: 25/11/18).
World Wildlife Fund (2017) Threats to Whales and Dolphins [online], Available at: http://wwf.panda.org/knowledge_hub/endangered_species/cetaceans/threats/, (Accessed on: 25/11/18).
World Wildlife Fund (2018) Blue Whale: Facts [online], Available at: https://www.worldwildlife.org/species/blue-whale, (Accessed on: 25/11/18).
Image References
Image 1: World Wildlife Fund (2018) Blue Whale: Facts [image], Available at: https://www.worldwildlife.org/species/blue-whale, (Accessed on: 25/11/18).
Image 2: IUCN (2018) Bangladesh creates new Marine Protected Area for Dolphins, Whales, Sharks and Turtles [image], Available at: https://www.iucn.org/content/bangladesh-creates-new-marine-protected-area-dolphins-whales-sharks-and-turtles, (Accessed on: 25/11/18).
Image 3: IUCN (2018) Bangladesh creates new Marine Protected Area for Dolphins, Whales, Sharks and Turtles [image], Available at: https://www.iucn.org/content/bangladesh-creates-new-marine-protected-area-dolphins-whales-sharks-and-turtles, (Accessed on: 25/11/18).
Image 4: knsnews.co.uk (2016) All you need to know about whale strandings in the UK and Europe [image], Available at:https://www.newscientist.com/article/2075274-all-you-need-to-know-about-whale-strandings-in-the-uk-and-europe/, (Accessed on: 26/11/18)
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