Sharksonline's Blog

Basking shark

Posted on: March 11, 2010

Above the basking shark

1. This shark is called the basking shark because it is most often observed when feeding at the surface and appears to be basking in the warmer water there.

2. The basking shark is found worldwide in warm waters and cold waters. But it prefers 8 to 14 °C (46 to 57 °F) temperatures, but recently has been confirmed to cross the much-warmer waters at the equator. It is often seen close to land, including bays with narrow openings. The shark follows plankton and therefore often visible at the surface. The basking shark is found from the surface down to at least 910 meters (2,990 ft).

3. The largest accurately measured was trapped in a herring net in the Bay of Fundy, Canada in 1851. Its total length was 12.27 metres (40.3 ft) and it weighed an estimated 19 short tons (17 t). Normally the basking shark reaches a length of between 6 metres (20 ft) and a little over 8 metres (26 ft). Some specimens surpass 9–10 metres (30–33 ft) but after years of large-scale fishing, specimens of this size have become rare.

4. Studies in 2003 proved that basking sharks do not hibernate, showing that they are active year-round. In winter, basking sharks move to depths of up to 900 metres (3,000 ft) to feed on deep water plankton.

5. Tagging confirms that basking sharks move thousands of kilometres during the winter, seeking plankton. It also found that basking sharks shed and renew their gill in an ongoing process, rather than over a short period. A 2009 study tagged 25 sharks and at least some migrate south for the winter. Remaining at depths between 200 metres (660 ft) and 1,000 metres (3,300 ft) for many weeks, the tagged sharks crossed the equator to reach Brazil. One individual spent a month near the mouth of the Amazon River. It is unknown why they undertake this journey. Some suspects it may to breed. And do not approaching boats (unlike great white sharks). They are harmless to humans if left alone and are not attracted to chum.

6. Basking sharks are social animals and usually in small numbers (3 or 4) but reportedly up to 100 individuals. Their social behavior is thought to follow visual cues. Although the basking shark’s eyes are small, they are fully developed. They may visually inspect boats. Females are thought to seek shallow water to give birth. These sharks have few predators but orcas and tiger sharks feed on them. Although it is unlikely that they are able to cut through the shark’s thick skin.

7. The basking shark feeds on plankton, small fish. They feed at or close to the surface with their mouths wide open. It relies only on the water that it pushes through its gills by swimming so it breath and feed at the same time.

8. Basking sharks developing embryos first rely on a yolk sac. Their seemingly useless teeth may play a role before birth in helping them feed on the mother’s unfertilized ova (a behaviour known as oophagy). Gestation is thought to span over a year (perhaps 2 or 3 years), with a small though unknown number of young born fully developed at  (4 ft to 6 ft). Mating is thought to occur in early summer and birthing in late summer, following the female’s movement into shallow waters. The age of maturity is not known but is thought to be between the ages of 6 and 13 and at a length of 4.6–6 metres (15–20 ft). Breeding frequency is also unknown, but is thought to be 2 to 4 years.

All of this info is from http://en.wikipedia.org/wiki/Basking_shark

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