Cetacean biodiversity of the Azores, explained

Why can we find such a wide biodiversity in the archipelago? What makes the Azores so special?

In the Azores, up to 25 different species of cetaceans can be seen. This is because on the one hand, the islands are located in the path of the migratory route for some species and, on the other hand, they are home for several others. In this post we will explain why the Azores are the perfect habitat for some cetaceans and why they are the perfect “pit stop” for others.

Geological and Climate involvement

Firstly, we need to understand that wild animals are driven by two main things: feeding and reproduction. Migratory species move between feeding grounds in nutrient-rich and typically cold waters and breeding grounds in typically nutrient-poor and warm waters. Non-migratory animals, on the other hand, are those who could find a way to survive in their breeding grounds, meaning that they can find food in the same area where they can breed. 

The Azores are 9 volcanic islands located in the central North Atlantic Ocean (38ºN, 28ºW) at the triple junction between the North American, Eurasian and Africa-Nubian plates, in the Atlantic fault. These 9 volcanic islands are divided in 3 groups: the western group composed by Corvo and Flores, the central group composed by Faial, Pico, São Jorge, Terceira and Graciosa and the eastern group composed by São Miguel, Santa Maria and Formigas Islets. Santa Maria is the oldest Island, emerging 8.12 Ma. Faial, which is the island where we are located, emerged in the Quaternary, 850 Ka. 

Due to this triple junction of plates, the Azores region includes several tectonic blocks in which the volcanic activity that formed the islands was originated. Moreover, this volcanic activity created a complex under-water landform with seamounts and marine canyons (Fig. 1). And this is what allows the Azores to be a hot spot. 

                                                               

FIG. 1. BATHYMETRIC MAP (FROM FRANÇA ET AL., 2009)

In marine ecosystems, life is typically found in steep slopes, not in plains. This is because marine primary production of matter relies mostly on phytoplankton. Phytoplankton is composed by plants suspended in the ocean, most of which are single-celled. They harvest light to transform inorganic matter into organic matter. This organic matter is the organic carbon that supplies energy and structure to the other organisms, so phytoplankton is the basis of the marine trophic chain. But phytoplankton needs two main things too: light and nutrients –chemicals such as Carbon, Nitrogen, Phosphorus, Iron, Calcium and others. Here is where under-water landform plays a role. Nutrients tend to drop to the deep bottom of the ocean because of gravity as they weight more than salty water. This stratification is problematic for phytoplankton as it needs light to do the photosynthesis, meaning that the phytoplankton’s growth is bound to happen only in the upper skin of the ocean, while nutrients are found in deeper layers of water. Luckily for phytoplankton –and therefore for almost every other organism in the world, since they ultimately depend on it– there is an event that allows this nutrient-rich deep waters to come to the surface and fertilize it. This phenomenon is called upwelling. 

Upwelling happens due to the wind affected by the rotation of the Earth. Winds can move water at right angles to the direction the wind is blowing, this is known as the Coriolis effect. As surface waters are pushed offshore, water is drawn from below to replace them, so the deep cold waters move upwards and swipe the sedimented nutrients with them causing the upwelling event. This upwelling event support blooms of phytoplankton, which is the ultimate energy base for large animal populations. 

Going back to marine landform, upwelling needs coastal lines to happen, as it forces the replacement of surface-waters by deep waters. The Azores, with its under-water landform creates this coastal line that allows a seasonal upwelling event to happen in the middle of the ocean, whereas without the archipelago that area would be a desert covered by salty water. In winter time the upwelling occurs, and by spring the bloom of phytoplankton hits the area. 

In climatological terms, the Azores is a transition zone as its temperate geographic location is tuned for a subtropical hint by the North Atlantic subtropical gyre. 

Migratory species

Between April and June, the migratory baleen whales (Mysticete) come to the Azores to feed off krill –tiny shrimp-like crustacean– and small schooling fish.  

Blue whales (Balaenoptera musculus) and Fin whales (Balaenoptera physalus) are perhaps the most well known out of all baleen whales. They travel north from tropical waters and stop by the islands as they can start feeding here. They are the biggest ones but not the only ones. In the Azores we can find 5 species of baleen whales: the Blue whale, the Fin whale, the Sei whale (Balaenoptera borealis), the Minke whale (Balaenoptera acutorostrata) and the Humpback whale (Megaptera novaeangliae). For instance, baleen whales can often be found in the Azores during Spring time. However, Blue, Fin and Sei whales are more frequent than the others. 

blue whale

The archipelago is also a destination for migratory toothed cetaceans (Odontocete). Those include the Atlantic Spotted dolphins (Stenella frontalis) that we can see during summer time, Stripped dolphins (Stenella coeruleoalba) that we can see from spring time until autumn, and both Short and Long-finned Pilot whales (Globicephala macrorhynchus and G. melas) that can be spotted in summer time.

atlantic spotted dolphins

Occasional sightings

The Azores, as described before, is like an oasis in the middle of the desert Atlantic Ocean. Its underwater landform is the perfect shelter for several species of fish, cnidarians and crustaceans. This –together with its water temperature– is the reason why some times special sightings happen; like the sighting of Orcas (Orcinus orca), False Killer whales (Pseudirca crassidens), Pygmy and Dwarf Sperm whales (Kogia breviceps and K. simus), Fraser’s and Rough-toothed dolphins (Lagenodelphis hosei and Steno bredanensis), North-Atlantic Bottlenose whale (Hyperoodon ampullatus) or another baleen whale, the Bryde’s whale (Balaenoptera edeni).

orcas

Resident species

All of the resident cetaceans in the Azores belong to the group of toothed cetaceans. Perhaps the iconic whale of the islands is the Sperm whale (Physeter macrocephalus) who is the biggest toothed animal on Earth. These whales are deep divers, capable of diving over 2.000 m deep to hunt their preys: deep species of squid and fish. The Azores is a great area to spot deep divers thanks to the proximity to deep waters as a result of them being volcanic islands. 

sperm whale

Moreover, the deep slopes are the perfect habitat for the species that deep divers feed off. This is the reason why –in addition to the North-Atlantic Bottlenose whale– 5 more species of beaked whales may be found around these waters. These species are Cuvier’s beaked whale (Ziphius cavirostris), Blainville’s, Sowerby’s, True’s and Gervai’s beaked whales (Mesoplodon denirostris, M. bidens, M. mirusand M. europaeus). Beaked whales are difficult to see because of their behaviour: they spend long periods of time underwater and their surface time is little, they live in small pods and tend to avoid noises and boats. 

sowerby's beaked whales

Furthermore, there are 3 resident species of dolphins: Bottlenose dolphins (Tursiops truncatus), typically coastal and most famous dolphin, Common dolphins (Delphinus delphis), typically found in large groups and deep areas, however they are easily found near the islands due to the steep slope of the bottom of the ocean, and Risso’s dolphins (Grampus griseus) typically found in small groups and also found in deep waters. 

common dolphin

Marine birds

Due to it being located in a transition area between tropical and temperate climate, the Azores is a primary nesting area. It hosts 100% of the world’s breeding population of Monteiro’s storm petrel (Oceanodroma monteiroi), 75% of the Cory’s shearwater world population (Calonectris borealis), 33% of Barolo shearwater world population (Puffinus baroli) and almost half the European population of Roseate tern (Sterna dougallii). 

cory's shearwaters

Whale watching in the Azores

There are different types of experiences involving cetaceans in different countries and each corner of the globe can offer unique encounters as each habitat is different and each species may behave differently in different areas. 

Given that the Azores is an environment of transition between the deep ocean and coastal ecosystems, it can offer food and shelter to several different species –including cetaceans–, thus being the home of a wide variety of marine life and therefore hosting an increased biodiversity. This means that when you join an ocean expedition in these waters, your chances of seeing several different species are higher than in other whale watching grounds. Although one must always bear in mind that (luckily!) we cannot control wild animals in their habitat and that we are just guests out there, higher biodiversity means higher chances to see more species. This is the magic of the Azores. Deep divers, oceanic species and coastal dolphins come close and can be seen in the same trip or even socializing if you are extremely lucky. 

sperm whale

Sighting statistics show that we can see around 20 different species of cetaceans every year –and this does not happen in many places in the world.

Author: Maria Serra. 

Acknowledges to all the photographers.

References

Alfonso, P. et al. (2020). The Azores: a Mid-Atlantic Hotspot for Marine Megafauna Research and Conservation. Frontiers in Marine Science - Deep-Sea Environments and Ecology 6.826.

França, Z. et al. (2009) Volcanic history of Pico and Faial Islands, Azores. An overview. Secretaria Regional da Ciencia.

Gaines, S., Airame, S. (2017) Upwelling. Ocean Explorer, National Oceanic and Atmospheric Administration (NOAA). 

Góis-Marques, C.A. et al. (2020) Oceanic Island forest buried by Holocene (Meghalayan) explosive eruptions: palaeobiodiversity in pre-anthropic volcanic charcoal from Faial Island (Azores, Portugal) and its palaeoecological implications. Review of Palaeobotany and Palynology (273) 104116. 

Portal da Biodiversidade dos Açores https://azoresbioportal.uac.pt/azores-species/#

Sigman, D. M., Hain, M. P. (2012) The Biological Productivity of the Ocean. Nature Education Knowledge 3(10):21.

Species directory (2020) NOAA Fisheries, National Oceanic and Atmospheric Administration (NOAA). https://www.fisheries.noaa.gov/species-directory