27.07.2018 – Marine Biodiversity

During todays tours we were able to observe four different cetacean species. Those included Atlantic spotted dolphins (Stenella frontalis), Bottlenose dolphins (Tursiops truncatus), Risso’s dolphins (Grampus griseus) as well as Sperm whales (Physeter macrocephalus). In addition, we saw Loggerhead turtles (Caretta caretta) and a variety of seabirds. Among those have been Cory’s shearwaters (Calonectris borealis), Bulwer’s petrels (Bulweria bulwerii) and Common terns (Sterna hirundo). Those are all apex predators in the ocean and therefore rank up high in the food web.

Such a great diversity and abundance of marine predators is a clear indication for a vivid ecosystem. This is based on the primary production in the ocean. Here around Madeira, the high productivity is mainly caused by upwelling water masses along the islands submarine slopes. That way, nutrients come up to the surface which enables phytoplankton to grow. Zooplankton relies on this plantal base of the food web. Those tiny ocean dwellers, mainly crustaceans, get eaten by small fish and those themselves are prey items for bigger fish species. At the top of this trophic pyramid, cetaceans, sharks, seabirds and seals constitute the hunters in the sea which have none or only a few natural predators.

Those favorable oceanographic conditions are the reason why we are able to observe this wide range of cetaceans on one day: from the small Spotted dolphins with around 2 m in length, over bigger members of the dolphin family like the Bottlenose and the Risso’s dolphins up to the truly gigantic Sperm whales measuring up to 20 m.

by Jan-Christopher Fischer

Sightings of the day

Stenella

08:30 (snorkeling) Atlantic spotted dolphins, Sperm whales

12:00 Bottlenose dolphins, Risso’s dolphins

15:30 Atlantic spotted dolphins, Bottlenose dolphins, Sperm whales

Ribeira Brava

13:30 Bottlenose dolphins

17:00 Bottlenose dolphins, Sperm whales