Posts Tagged 'Fish fauna'

Sunday article – Vanishing Species: Sharks

Sunday Article by Mohan Pai

 
 
Shark
(Selachinmorpha)

The great predator.
 
 
Virtually unchanged for more than 400 million years, shark’s streamlined bodies and amazing sensory systems fit the mold of a perfect predator.
 
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs. Sharks are found in all seas and are common down to depths of 2,000 metres (6,600 ft), and some live even deeper but they are almost entirely absent below 3,000 metres (9,800 ft). They generally do not live in freshwater, with a few exceptions such as the bull shark and the river shark which can live both in seawater and freshwater. They respire with the use of five to seven gill slits. Sharks have a covering of dermal denticles that protect their skin from damage and parasites and improve fluid dynamics so the shark can move faster. They have several sets of replaceable teeth. Well-known species such as the great white and the hammerhead are apex predators at the top of the underwater food chain. Their extraordinary skills as predators fascinate and frighten us, even as their survival is under serious threat from fishing and other human activities.
 
 Extraordinary Sensory System
Sharks have sensory organs unlike any other creatures. Most sharks can:
* Pick up sound waves from more than 5 kilometers.
*Detect a single drop pf blood in an amount of water contained in an Olympic size swimming pool.
*Register the heightened body tension of a wounded or panic-stricken creature.
* locate prey in total darkness.
 
Unlike bony fish, sharks have no bones; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. Sharks also have no swim bladder (unlike bony fish).
 
 Size & Shape
 
There are many different species of sharks that range in size from the size of a person’s hand to bigger than a bus. Fully-grown sharks range in size from 7 inches (18 cm) long (the Spined Pygmy shark), up to 50 feet (15 m) long (the Whale shark). Most sharks are intermediate in size, and are about the same size as people, 5-7 feet (1.5-2.1 m) long. Half of the 368 shark species are under 39 inches (1 m) long.
 
 Sharks have a variety of body shapes. Most sharks have streamlined, torpedo-shaped bodies that glide easily through the water. Some bottom-dwelling sharks (e.g. the angelshark) have flattened bodies that allow them to hide in the sand of the ocean bed. Some sharks have an elongated body shape (e.g., cookiecutter sharks and wobbegongs). Sawsharks have elongated snouts, thresher sharks have a tremendously elongated upper tail fin which they use to stun prey, and hammerheads have extraordinarily wide heads. The goblin shark has a large, pointed protuberance on its head; its purpose is unknown.
 
 There are about 368 different species of sharks, which are divided into 30 families. These different families of sharks are very different in the way they look, live, and eat. They have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes. Some types of shark are very rare (like the great white shark and the megamouth) and some are quite common (like the dogfish shark and bull shark). Sharks belong to the group of cartilagenous fish, the Elasmobranchii, that includes the sharks, rays, and skates.
 
Sharks play a vital role in our ecosystem as part of nature’s complex system of checks and balances. Known as apex predators, they are at the top of the food chain. Many sharks prey upon wounded and sick animals, keeping the populations of various species healthy and in balance, while others scavenge the ocean by feeding on dead animals or by filter feeding.
 
According to United Nation’s Food and Agriculture Organization (FAO) approximately 100 million sharks are killed each year. This does not include those caught as bycatch (non-targeted animals caught unintentionally and wasted), which is largely unreported. Many sharks also fall victim to finning, the practice of cutting shark’s dorsal, caudal and pectoral fins, then discarding the still-living shark into the sea to die. Sharks play a vital role in our ecosystem as part of nature’s complex system of checks and balances. Known as apex predators, they are at the top of the food chain. Many sharks prey upon wounded and sick animals, keeping the populations of various species healthy and in balance, while others scavenge the ocean by feeding on dead animals or by filter feeding.
 
Most sharks have no predators, but biological characteristics such as slow growth, late sexual maturity and low number of offsprings make sharks susceptible to almost any fishing pressure. Most species are either fished to capacity or overfished worldwide and for products like shark meat, fins and cartilage contribute to their decline.
 
In India, the bull shark is often called the Sundarbans or Ganges shark and it is found in the Ganges and Brahmaputra rivers of West Bengal and Assam in eastern India and adjoining Bangladesh.Sharks of the family Carcharhinidae are the most important group, dominating the fishery all over the world, and this applies equally in India.
 
 
SHARK ATTACKS
 
When some sharks (like the Great White or the Gray Reef shark) turn aggressive prior to an attack, they arch their back and throw back their head. This places their mouth in a better position for taking a big bite. They also move their tail more acutely (probably in preparation for a chase). Sharks do not normally attack people, and only about 25 species of sharks are known to attack people. Sharks attack fewer than 100 people each year. Many more people are killed by bees or lightning.
The sharks that are the most dangerous to people are the great white shark, the tiger shark, the bull shark, and the oceanic whitetip shark. The bull shark is the most frequent attacker of people as it swims in very shallow waters where people swim and is a very plentiful shark. Some of the other sharks that are known to have attacked people include the gray shark, blue shark, hammerhead shark, mako shark, nurse shark, lemon shark, blacktip reef shark, wobbegongs, sandtiger, spitting sharks, and the porbeagle. Some people believe that sharks mistake people (especially people swimming on surf boards) for seals and sea lions, some of their favorite foods.
 

References: Wikipedia, enchantedlearning.com

 

MY BLOG LIBRARY

For some of my articles visit:

http://mohanpaiblogger.blogspot.com/
http://mohanpaisarticles.blogspot.com/
http://biodiversity-mohanpai.blogspot.com/
For some key chapters from my book “The Western Ghats”, please log on to:http://westernghats-paimohan.blogspot.com/
For detailed blog (6 Chapters from my book) on Mahadayi/Mandovi River Valley, please log on to:http://mohan-pai.blogspot.com/
For the book ‘The Elderly’ please log on to:
http://omashram.sulekha.com/blog/posts.htm
http://oldagecare-paimohan.blogspot.com/
You can also access my blogs on Sulekha and WordPress
https://mohanpai.wordpress.com/
http://mohanpai.sulekha.com/blog/posts.htm
For my book “The Flight of Gods – Hindu Temples & Shrines of Goa” please log on to:
http://flightofgods.sulekha.com/blog/posts.htm
http://flightofgods.blogspot.com/
For “Miscellany” log on to:
http://paimohan-mohanpai.blogspot.com/
(Traditional Hindu Central Courtyard Houses of Goa)
email: mohanpai@hotmail.com

 
Advertisements

Vanishing Species – The Blue Whale

An article by Mohan Pai

 
The Blue Whale
Balaenoptera musculus


Critically endangered Blue Whale is the largest animal to have ever lived, almost as big as Boeing 737 and even larger than the biggest dinosaurs.

 With lengths up to 100 feet (30 m) and weights up to 150 tons (136 metric tons), the blue whale is the largest animal that ever lived on this planet. An average individual is 70 feet (21 m) long and weighs 100 tons (90 metric tons). The female, which is larger than the male, gives birth to a calf that averages 25 feet in length and weighs about 2 tons. The calf drinks about 106 gallons of milk every day. An average adult has almost 2,500 gallons of blood and burns up to 3 million calories a day. Its heart weighs more than a ton and the tongue alone weighs about 2 tons! Linnaeus must have had his tongue in his cheek when he gave this species the Latin name “musculus,” which means “little mouse.”As the common name indicates, the upper parts of the body are mottled blue-gray. The undersides are whitish or light yellow. This whale has a relatively small dorsal fin and black baleen plates. The straight, column-like water spout can reach 20 feet into the air. Speeds of up to 23 miles per hour (20 knots) have been recorded for the blue whale.
 For many, many years ancient sailors had rare encounters with these gigantic ocean mammals and were terrified by their overwhelming size and powerful tails. You can understand a little of the fear and trepidation they might have felt upon seeing these huge, mysterious creatures for the first time. Today we know them to be virtually harmless to humans and that they have quite a bit in common with us – they, too are warm-blooded mammals that must breathe air. They are highly social animals with complex languages and intelligence. Most importantly, they are not monsters at all, but gentle giants we have come to respect, admire and protect.
 
Size comparison against an average human
 Diet
Blue whales diet consists mainly of krill, a tiny shrimp that lives in tremendously large schools in almost every ocean of the world. Krill is probably one of the most plentiful food species (outside of insects) anywhere on earth. It’s got to keep up with the blue whale’s big appetite. A big blue can eat over a thousand krill at one time swallowing them with a tongue that weighs as much as an elephant! Blue whales eat the krill using a special type of filter on their mouths called a baleen. By gulping enormous amounts of sea water containing the live krill the blue whale closes its mouth and flushes the sea water back out through the filter leaving the krill behind for it to swallow. Small fish and plankton are also favorite food items of the whale. It takes about 8,000 lbs/3600kg of fresh seafood a day to keep the blue whale well fed.
 Vocalisation
Probably the most spectacular thing about blue whales that’s bigger than big is the sounds they make. Scientists have measured the low-frequency (deep rumbling) sounds they make when they communicate with each other by using a decibel meter. Some of their vocalisations have been recorded as loud as 188 decibels and can be heard as far as 530 mi/848km away. To give you an idea of just how loud 188 decibels is a commercial jet taking off makes a sound of 120 decibels. That makes whales, by far, the loudest living thing anywhere on earth!
 Range
Found in the Atlantic, Pacific, Arctic and Indian Oceans, with a range that extends from the periphery of drift-ice in polar seas to the tropics . Three main populations persist: one in the southern hemisphere, one in the North Pacific and one in the North Atlantic ).
In India, the Blue Whales have been washed ashore in Karnataka, Maharashtra, Gujarat, Tamil Nadu, Kerala and Andhra Pradesh.
 
Red area indicates the range of the Blue Whale

Life History

Blue whales migrate several thousand miles to wintering grounds and fast for the duration of their stay; the fat on their body is enough to see them through the whole winter. The mating season occurs for 5 months over the winter. A single calf is born after a gestation period of one year. It nurses for 7 months and will reach sexual maturity at 5-15 years of age. Females give birth every 2-3 years.
 Status
The blue whale is currently one of the world’s most endangered whales. It was not hunted until somewhat modern techniques made them more easily attainable.
 Blue Whales were abundant in nearly all the oceans until the beginning of the twentieth century. For over 40 years, they were hunted almost to extinction by whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 Blue Whales worldwide, located in at least five groups. More recent research into the Pygmy subspecies suggests this may be an underestimate. Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000). There remain only much smaller (around 2,000) concentrations in each of the North-East Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic, and at least two in the Southern Hemisphere.

Blue Whale skeleton, outside the Long Marine Laboratory at the University of California, Santa Cruz

Major Threats

The main threat in the past was direct exploitation, which only became possible in the modern era using deck-mounted harpoon cannons. Blue whale hunting started in the North Atlantic in 1868 and spread to other regions around 1900 after the northeastern Atlantic populations had been severely reduced. The Antarctic and North Atlantic populations were probably depleted to the low hundreds by the time whaling ceased, but are increasing . Blue whales have been protected worldwide since 1966, although they continued to be caught illegally by former USSR fleets until 1972. The last recorded deliberate catches were off Spain in 1978.

 

References: Dept. Of Environmental Conservation, New York State, Wikipedia, IUCN Red List.

 

MY BLOG LIBRARY
For some of my articles visit:
http://mohanpaiblogger.blogspot.com/
http://mohanpaisarticles.blogspot.com/
http://biodiversity-mohanpai.blogspot.com/
For some key chapters from my book “The Western Ghats”, please log on to:
http://westernghats-paimohan.blogspot.com/

For detailed blog (6 Chapters from my book) on Mahadayi/Mandovi River Valley, please log on to
:http://mohan-pai.blogspot.com/

For the book ‘The Elderly’ please log on to:
http://oldagecare-paimohan.blogspot.com/
http://omashram.sulekha.com/blog/posts.htm
You can also access my blogs on Sulekha and WordPress:
http://mohanpai.sulekha.com
https://mohanpai.wordpress.com/
For my book “The Flight of Gods – Hindu Temples & Shrines of Goa” please log on to:
http://flightofgods.sulekha.com/blog/posts.htm
http://flightofgods.blogspot.com/


Blog Stats

  • 65,596 hits

Flickr Photos

Top Rated