International Whale Shark Day!

30th Aug 2017

30th August is International Whale Shark Day, so to celebrate these wonderful animals the ORCA team have pulled together a few facts that shows differences and similarities between whale sharks and their namesakes.

The basics

Though they are both giants of the ocean, there aren't many ways that whale sharks are similar to the whales ORCA are used to spotting out at sea.

As we know, whales are mammals just like humans are, and are a part of the group known as cetaceans (whales, dolphins and porpoises). Whale sharks, however, are a part of the elasmobranch (sharks, skates and rays) family and are therefore classified as cartilaginous fish. 

Despite this, both do have similar diets - many of the larger whales of the baleen subgroup eat krill and small fish by filtering water through the long strips of keratin (or baleen). Whale sharks are also filter feeders eating krill, plankton, fish eggs and small fish. However, they filter their food in a different way, actively sucking in their prey and filtering them through their gill arches.

Behaviours

When it comes to moving and living in the ocean, there isn't much to connect the two. Whales use vertical tail movements to propel themselves through the water, whilst sharks move ther tails from side to side to achieve the same effect. This due to the fact that whale tails (or flukes) evolved from legs and the vertical motion is a remnant of the hinged joints their ancestors had.

As a rule, whale sharks inhabit shallow, coastal waters, typically roaming seas at around 50m depth (though they can dive up to 1000m). Species of cetacean vary greatly in their distribution, but larger species are more commonly seen in deeper waters and some species can reach depths of over 2000m.

Anatomy

Whales are reliant on surfacing to breathe air through their blowholes, although some species able to stay under water for hours at a time before returning to the surface. For example, a tagged Cuvier's beaked whale was recorded to remain under water for 137 minutes! Sharks are able to filter oxygen out of the water using their gills, so do not need to surface to breathe.

Senses differ greatly as well - sharks have excellent smell and vision whilst whales have developed a sensitive auditory system. Sharks also have a system of electroreception, using electrical impulses in the water to hunt out prey around them.

Whales have a skeletal system made of bone, whereas whale sharks have a system composed of cartilage - this makes them much lighter relative to their size.

Threats

Unfortunately whale sharks, like many species of whale, are under threat. They are hunted for their fins and meat, with the global black market still being incredibly lucrative. Whale sharks are also vulnerable to ship strikes, just like many of the larger baleen whales, as they spend time near the surface and are very slow moving.

Overfishing, climate change, pollution and a range of other threats also affect these wonderful animals, and they are listed as Vulnerable on the IUCN Red List.