Basking Shark

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The basking shark may look more fearsome than its smaller, more fierce relatives. But despite its cavernous mouth and huge dorsal fin, it is a placid, harmless giant. The baking shark spends much of the year cruising near the surface of temperate oceans with its giant mouth wide open. Despite its huge size up to 30 feet it feeds only on tiny sea creatures that it filters from the water.

Food and Feeding: Sharks are renowned as fierce predators. Yet the two largest species, the basking shark and the whale shark, have a completely different feeding behavior. Like manta rays and great baleen whales, they sustain their enormous bulk by swallowing great quantities of plankton tiny ocean creatures that include fish eggs, copepods, and arrow worms. By cruising gently through the ocean with its great mouth yawning open, the basking shark draws in tons of water. The water passes out through five wide gill slits on each side of the sharks neck after it has been strained through rows of gill rakers. Thousands of these mucous covered bristle like structures lie next to the gills. Each is about four inches long. When the basking shark opens its mouth, the gill rakers spring up to form dense fringes that trap the tiniest prey.  The basking sharks wide, gaping mouth acts like an enormous sieve. To nourish its huge body, the basking shark spends a large amount of time feeding near the surface of the water. A system of gill rakers ensures that no food escapes the basking sharks mouth.

Habits: The basking shark is known for cruising slowly. It rarely swims faster than three miles an hour and is often seen at the surface of the water. It is named for its habit of lying still its back breaking the surface and its great dorsal fin protruding as if were basking in the sun. Although they are often seen alone or in twos and three's, basking sharks sometimes gather in schools of 50 or even more than 100 individuals. Basking sharks are seen most often in the summer, when temperate waters are rich in plankton. In winter this food supply dwindles, and it is thought that the sharks cannot take in enough plankton to remain active. Instead, they may retreat to deeper water or possibly the sea floor. There they lie still and stop feeding. Their metabolic rate drops, and they rely on deep currents to bring oxygen to their gills. In European waters basking sharks appear to shed their gill rakers in winter, making feeding impossible. By spring, when plankton starts to flourish again, they have acquired new gill rakers. The basking shark is a gentle giant of the ocean.

Breeding: Little is known about the breeding behavior of the basking shark. It is known, however, that egg production is strikingly different from that of most sharks. Sharks generally produce a small number of large eggs. But a female basking shark may produce six million eggs that are 0.02 to 0.2 inches in diameter. Fertilization is internal, and the young seem to develop inside the mother's body, as in most sharks. Why the female produces such a huge number of eggs is unclear. It may be that the mass of unfertilized eggs provides nourishment for the developing embryos. The end result is only one or two offspring. At birth, basking sharks are already about five feet long. Immature sharks can grow up to 15 feet. At this stage the sharks have long, fleshy snouts, with a curved hook at the tip. Basking sharks generally reach sexual maturity when they are 15 to 20 feet long.

Nature watch: Basking sharks are summer visitors to both the Atlantic and Pacific shores of North America, in coastal and offshore waters. They start to appear in late April and early May, when marine copepods, a staple food, are abundant near the surface. By the end of November, the baking sharks have disappeared, probably to deep water for a long winter fast. The tall dorsal fin and the sheer size of a basking shark make it easy to recognize.

Key Facts: Sizes, Breeding, Lifestyle, Related Species:

Length: Averages 25-30 ft.
Weight: 4-4 ½ tons

Sexual maturity: 2-4 years
Mating season: Spring in the North Atlantic
Gestation: May last 3 years
No. of young: 1, occasionally 2

Habit: Occurs singly, in small groups, or in schools. Slow moving; often appears at the surface
Diet: Plankton
Life span: Not Known

Related Species: The basking shark is in a family by itself. But it is related to thresher sharks and mackerel sharks
Distribution: Found in temperate waters in both the northern and southern hemispheres
Conservation: The basking shark is thought to be low in numbers, but there are no accurate details about population figures. There is some concern that fishing may be reducing the basking shark's feeding areas.

Special Adaptations of the Basking Shark:
Filament: Thin layers of orange red flesh that absorb oxygen from the water
Mouth: As the shark moves through water, its mouth is open
Gill rakers: Sticky, mucous covered bristles trap food
Feeding: Water, oxygen, and plankton are sucked into the mouth and filtered through the gill rakers. The rakers trap the food but allow the water and carbon dioxide out through the five gill slits on each side of the mouth.

Did You Know:
The basking shark is the second largest fish in the world after the whale shark.
The largest basking sharks on record include a 39 foot specimen trapped in a net off southeast Canada in 1851, another 39 foot shark caught off Portugal in 1865, and a 45 foot giant caught off Norway in the 1890s.
Cruising at about 2 knots, a basking shark can filter 1,000 tons of seawater through its mouth in an hour.
There are reports of basking sharks leaping completely out of the water. They may have been trying to drive off parasites, such as lamprey, attached to their bodies.
Basking sharks have never been major fishing prey. But some have been fished off Ireland, Scotland, and Norway. The liver from a single shark can weigh 1,500 pounds and yields valuable oil.

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