Can we see sharks on your boat trips?

/Ilustration by Katrin Wahner

The answer is YES!

Often we get asked by our guests about sharks. And yes, there are sharks around. It is their natural habitat!

Madeira is a high sea island and situated far off the african continental shelf. There is an immense spectrum of very different marine life in the waters around our Island. There are also big fish like Marlins, Swordfish, Barracudas and others. On our trips, we see, besides rather seldom species like Ocean Sunfish, Rays or big squids, also sharks. Mostly these are brief encounters, at which you can only see a dorsal fin or barely the contours of their bodies. Sharks are very shy, so they escape quickly and dive.

The most common sighted shark species around Madeira are: hammerheads, mako, blue and different greyshark species. But there are much more species around, also further down in bigger depths. Sharks are fascinating animals and constitute -from an evolution-biology point of view- a very old suborder of the vertebrates. Many millions of years, they lived on our planet, long ago, before mankind appeared. As cartilaginous fish, sharks are on top of the marine foodweb. As top predators, they play an important role for healthy marine biotops. Their “job” can be compared with a kind of “health-police” of the sea.

Shark Sighting

On September 22nd Claudia (Guide), Daniel (Skipper) and some of the guests on a Stenella tour got to see, for a short moment, two sharks. The animals had a body length of about 2-2,50m and they were swimming near a Espada fishing boat. The fishermen were just hauling inbord their fishing gear. They were taking off remaining bait from the longline hooks and throwing the baits back in the water. Probably and unintentionally, they attracted the sharks by this.

Maybe (unfortunatelly, we weren’t able to take pictures) the sharks were specimen of the “Oceanic white tip shark” (Carcharhinus longimanus). A family of requiem sharks (Greysharks; Carcharhinidae), which inhabit worldwide tropical and subtropical high seas. Oceanic white tip sharks are counted to the bigger shark species. Due to intensive high sea fishing and because of the so called “Sharkfinning” methode, many sharkspecies, including the “Oceanic wihite tip shark” are threatend wordwide from extinction. IUCN put the species on the redlist index of endangered species.

General information about the “Oceanic white tip shark”

Appearance:

Size: up to 3,90 m; average size rather 2,50 – 3,00 m.

Distinctive features: long and rounded first dorsal fin with white tip; colour of back can be grey-brown up to bronze coloured; colouration can vary according to region.

Way of living:

Sharks are both diurnal and nocturnal. During the day, they rather stay close to the water surface. Since they do not have a gas-filled swim bladder as fish do, most sharks species have to keep on moving to avoid sinking down. Instead of swim bladder, sharks rely on a large liver filled with oil, providing a little bit of boost. Sharks feed on tuna, mackerel, swordfish and barracuda, as well as on sea turtles, dolphins, squid and similar prey. They also eat discarded trash from ships and carcass of other marine animals (like whales f.e.).

The “Oceanic white top shark” is described as curious up to importunate with scuba divers. Because there are some reported accidents/attacs, this species is considered to be potentially dangerous for humans. However, the danger of sharkattacs is often exaggerated. The probability of getting hit by a stroke of lightning is much higher than a shark attack.

Short information about sharks and their worldwide threat 

Since, already, millions of years (350 million years) sharks are living in our oceans, long ago before human even appeared on earth. Sharks are excellent adapted to the aquatic way of living and have available some extraordinary sensory organs. For example, they have keen olfactory senses (smell), located in the short duct between their nasal openings. Some species are able to detect very little amounts of blood in seawater from a large distance. Sharks use “ampullae of Lorenzini” (electroreceptor organs) to detect electromagnetic fields that all living things produce. With this, they can even find prey, which is hidden in the sand. Ocean currents moving in the earths magnetic field also produces electric fields, which sharks and other marine animals can use for orientation. In the oceans, sharks take care of the ecological balance. Big shark only have to fear, besides humans, killer whales as predators.

Today, many shark species are threatend by extinction and their populations are often overfished. Besides Asiatic fishing fleets, also european nations hunt sharks. Often the shark meat is hidden under product names as “curled strip of smoked dogfish, “sea eel” and other names. Furthermore, sharkmeat is used as animal food, or gets processed for fish meal. It is as well merchandised in medical shark cartilage products. Since shark fin soup, in Asian countries is a status symbol, customers pay high sum of money for this. Extremely cruel is the method of so called “Sharkfinning”. Fishermen then cut off the sharks fins, from living sharks and then throw the mutilated, still living torso over board like waste. Besides this, similar to marine mammals, sea turtles and other marine animals, sharks also get caught in the “walls of death” (lost drift nets) and drown. The increasing loss of the “sharks nursery grounds”contributes to important biotops getting short. This is for example the case with clearing off coastal mangrove forests, in order to cultivate there fish and shrimp farms.

How to distinguish, at first sight, sharks (fish) from dolphins (marine mammal)?

/Ilustrations by Katrin Wahner

Some external features for the determination between fish and marine mammal:

First of all, sharks have (different to dolphins), a vertical tail fin. Tails of swimming sharks, are moving laterally back and forth. Compared to this, the horizontal tail fluke of a dolphin is moving up and down. Sharks have a longer upper jaw (shorter lower jaw) and their flat head is in many species pointed. On the contrary, most dolphin species have a distinctive “beak” (upper and lower jaw have same length) and have normally a well formed forehead (melon).

Sharks have 5-7 gills on the sides of their head (behind eyes). Dolphins breath air with a single blowhole on top of their heads.

/Written by: Astrid Haas