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14, Feb, 2014

Shark Sightings – Whaleshark!

Posted in Diving Conditions and Weather, Diving News, Latest News, Marine Life, Sharks & Rays by kimmy

Scubafish are having a fabulous February – diving conditions are superb, sightings of manta rays at Hin Daeng & Hin Muang remain on almost every trip (since the middle of December), and we’ve even been visited at Ko Haa by leopard sharks and a whaleshark over the last 2 weeks! In this particular post we shall discuss the whaleshark.

 

Whaleshark:

Just after surfacing from our first dive yesterday we received the news from another boat that there was a whaleshark in the water just off Island 1 at Ko Haa, less than 50 meters from where we were and it was there – RIGHT NOW!!! Without much delay everybody jumped back in and swam or snorkelled in the general direction indicated (by a few snorkelers already in the water). We are happy to report that everybody on the boat saw this gentle giant, including our captain and crew from the surface.

shark sighting

The whaleshark itself was a juvenile, around 2.5 meters in length, and was cruising around in the top 5 meters of water between islands 1, 2 and the north corner of island 3 for almost 2 hours!

Shark sightings

Scubafish are proud to be active members of the Lanta Whale Shark’s DOTS Activity, as initiated by SAMPAN (Supporting Andaman Marine Protected Areas Network). The Lanta Islands are known to be one of the migratory routes and feeding grounds of the whaleshark. DOTs members support SAMPAN by providing additional information, completing surveys, and recording whaleshark sightings so as to monitor the population and distribution in this area and aid in the conservation and study of this endangered species.

shark sightngs

shark sightings We do this using the DOTs shooting technique, meaning we photograph the left side pattern of dots from the base of the dorsal fin to the last gill slit of the whaleshark. This pattern of dots on the skin is as individual as human fingerprints, so allow for a specific identification by ECOCEAN research, who compare the pattern with thousands of records from their worldwide database.

Did you know? Prior to the mid-1980’s there were fewer than 350 confirmed whaleshark sightings worldwide, and relatively little is known about the existing overall population, or status.

 

Whaleshark

 

Whaleshark Facts

Coloration
Adult whale sharks’ skin is up to 10 cm thick. There are three prominent ridges running along each side of the shark’s body. The underside of the whaleshark is white, whilst the back and side surfaces are either grayish, bluish or brownish, with light yellow dots between pale, vertical and horizontal stripes (random dots and stripes). It is thought this pattern and colouration is a form of camouflage – either resembling a school of small fish or sunlight reflecting of a shallow reef.

Fins
Whalesharks have 2 dorsal fins (on its back) and 2 pectoral fins (on its sides). The first dorsal fin is much larger than the second dorsal fin, and set rearward on body. The caudal fin (tail) is semi-lunate in adults; in small juveniles the upper lobe is considerably longer than the lower lobe.

Mouth
Whalesharks have a huge mouth which can be up to 1.4 m wide!!! In the process of feeding, the mouth can possibly extend two or three times that width. The whaleshark can filter up to 6000 litres of water per hour! Whereas in most shark species the mouth is located on the underside of the head, the mouth of the whaleshark has evolved to be at the tip of the snout.

Teeth
The original name “Rhinodonte” means “rasp tooth”. The whaleshark has 3,000 tiny teeth (each only around 3mm) in 11-12 rows. They play little use in feeding, only processing larger food items, such as small tuna and mackerel that are occasionally captured and cannot pass through the whaleshark’s gullet.

Gills
Whalesharks have 5 very large gill slits.

Feeding
Whalesharks swim with their mouths open scooping masses of water into their mouth and through gill rakers (spongy tissue) between their 5 large gill arches. This is known as filter feeding and it’s function is to filter the nourishment from the water. Anything that does not pass through the gills is eaten and water is expelled through 5 pairs of gill slits.

Understanding the whale shark diet is especially important because food sources determine much of its movement and location. Its food list includes the eggs of little tunny (Euthynnus alletteratus), mackerel, sardines, anchovies, copepods (small crustaceans), shrimp, plankton, krill and squid.

Size
Whalesharks are the largest fish in the world. Their length is up to 20 metres and weight is up to 20 tons. Females are larger than males (like most sharks).

Breeding
They do not breed until they are between 25-30 years old, and it’s thought they may breed and give birth out in the open ocean. Whalesharks are viviparous, giving birth to live young.

Status
The Whaleshark is fully protected under the Fishery Act, 1947 and ‘vulnerable to extinction’ by the World Conservation Union (IUCN).

whalesharkanatomy

 


 

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