Sharks and rays

Did you know that rays and sharks share the same class? The class is called Chondrichthyans in latin, which stands for cartilaginous fishes.

In popular media, sharks are commonly depicted as dangerous animals, ready to hunt for human flesh at any time. Despite this (obviously wrong) image, swimming with sharks or rays is more popular than ever. These species are distributed around the worlds oceans and shark tourism is fairly new business. Related to that, sustainable tourism appears to be a side issue for most of the upcoming company’s and managing these issues on a larger scale is hard. Short term thinking might seem to be more financially rewarding, though in the end can be devastating for the shark/ray population and its related food web. This in turn affects fisheries ánd the touristic company’s themselves. In response to that, WWF has developed a guide to responsible shark and ray tourism, which interests me most. I’d like to tell some more about sharks and the effects irresponsible tourism can have on them.

Shark and rays – cartilaginous fishes
The term cartilaginous reflects the fact that the skeletons are composed of cartilage, a flexible tissue that is different from bone. There are around 1200 species of chondrichthyans known. The graph below shows there are more species of ray than sharks. Chimaeras are the third type of chondrichthyans, distinguished by the fact that they have swim bladders, which they use to control their buoyancy (how cool!).

chondricthyans species numbers - William E Bernis

Sharks are easy to classify based on their body shape and fin shape, size and placement. As you may know the caudal fin of a white shark is more or less symmetrical, with the upper and lower lobe equal sized. As a comparison a tiger shark fin is more sickle shaped. In rays the pectoral fins have attached to the head and the pelvic fins.

Most sharks are apex species. This means that the mature animal does not have any natural predators and thus is at the top of the food chain. But not all sharks are also considered top predators. Whale sharks are filter feeders, not preying on other predators but feeding on krill, larvae and plankton. A healthy diet it seems; they are the largest shark species.

Responsible tourism – whale sharks

Whale sharks are an exemplary species desperately in need of sustainable eco-tourism. My experiences in the Philippines shows for the struggle many tourist have / will have when on holiday. As you know I’m fond of marine life, just like Rob, so we were interested in swimming with whale sharks in Cebu. In fact we’d even booked a whale shark trip. We already read some disconcerting things on the internet, so we tried asking critical questions. Are the whale sharks harmed in any way? Is it their natural habitat? But if you’re poorly informed like me at the time you ask the wrong questions and may believe the (dodging) answers. So we booked for the other day after being reassured nothing was wrong…

That night during a walk on the beach Rob and I came across this sign.

DSCN0062

This sign made us change our mind. We canceled (best choice ever). We discussed the topic with our local dive school who are part of Green Fins and did more research on the internet. This sign, in fact, was the start of my interest in marine biology and conservation.

Jules from DontForgetToMove.com tells the same story and also explains why the whale shark tours in Cebu are harmful (see link under Sources below). There are multiple ways the tours affect the whale sharks. In summary

  • The whale sharks are attracted by the local fishermen using krill to continuously feed the sharks. ‘Because of this, the whale sharks are now spending up to 6 hours feeding in Oslob, losing out on some of the key nutrients that they gain from foraging naturally.’
  • The whale sharks are tempted to stay in the area because they’re being fed. This discontinues their natural migratory behaviour. Although research is limited, it is expected to affect their reproduction due to changing breeding habits.
  • Since the sharks swim shallowly, the boat’s propellers induce serious injuries. It is said that none of the Oslob whale sharks is without these cuts.
  • Touching whale sharks (or any fish species) gives a risk of skin disease to the animal. Human skin oil and bacteria (and sunscreen) are not natural for fish and can lead to skin inflammation or open wounds.

A change in feeding pattern or decrease in the number of any apex species can (and will) lead to a trophic cascade: reciprocal changes in the relative populations of predator and prey through a food chain. More on that in another blog post.

WWF – Project AWARE – Manta Trust

The book these partners created is called Responsible shark and ray tourism. A guide to best practice. ‘The Guide, developed in collaboration with science and industry, aims to create well-managed shark and ray tourism operations, conserve species and benefit local communities.’ Although it is written for NGO’s and resource managers, it might be interesting for you to read about what your tour operator should be doing to minimize impact. Please be sure to conduct thorough research on the internet before signing up for any shark/ray tour.

Sources

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