27.03.2019 – A swimming statistic

Our traditional boat set out onto a rather choppy ocean this afternoon, which didn’t make finding cetaceans easy for our team. Our search area extended to the calmer waters near the coast of Ribeira Brava, where our captain, Filipe, steered the ship towards the island to slowly head back to Calheta. Suddenly, one of our guests pointed at a fin slicing through the surface. This fin didn’t belong to any cetacean; it was a shark swimming at the surface.

Being an oceanic island, Madeira serves as a potential habitat for several pelagic sharks including the Blue shark (Prionace glauca), the Mako shark (Isurus oxyrinchus), the Bigeye Thresher shark (Alopias superciliosus) and the Hammerhead shark (Sphyrna lewini). Occasionally we also see traces of Cookie-cutter shark (Isistius brasiliensis) bites on some older cetaceans.

While there traces can be spotted, shark sightings are unfortunately a rarity during our trips. Of course this is partially due to their evasive nature and the fact that they don’t need to surface to breathe. Most sharks however, apart from the Carpet sharks (Orectolobiformes), do need to keep swimming to breather. This is necessary to maintain a countercurrent flow of blood and oxygen that establishes a concentration gradient, allowing the exchange of oxygen between the two fluids. Carpet sharks can actively pump water over their gills.

Another reason such sightings are so rare is the fact sad fact that there aren’t many sharks around anymore. Apart from being frequent by-catch victims on long-lines used to catch tuna or black-scabbard fish, sharks are still exploited as for their dorsal fins. And this problem hits closer to home than we think. Portugal is ranked 16th worldwide and third among all EU member states in their catch of sharks. Makos and Blue sharks are particularly sought after and often targeted as trophy fish during Big-Game fishing activities. Portugal and Spain also happen to be the only two EU countries that allow at-sea fin removals to their fishermen, an activity which often results in the finless shark being discarded back into the ocean and bleeding to death.

The shark we saw today was perhaps a Thresher shark and was swimming within one nautical mile off fishing buoys carrying long-lines for Black scabbard fish. Let’s hope this magnificent creature doesn’t end up being another statistic.

By Paula Thake

Sightings of the day

Ribeira Brava

14:30 No cetacean sighting