26.01.2019 – Cause & Effect

We had a wonderful trip this morning with a small group of guests who were lucky enough to see Short-beaked common dolphins (Delphinus delphis), Bottlenose dolphins (Tursiops truncatus) and Short-finned pilot whales (Globicephla macrorhynchus). As the apex predators in most marine ecosystems, cetaceans act as important indicators for the health of marine food webs which in turn dictate the health of our oceans.

And boy, do we need our oceans. Since centuries mankind has colonized coastlines thriving off the ocean for food, resources and the transport of provisions. Over time, the degree to which we rely on our oceans has increased but what we give our generous planet in return is very questionable. The health of our oceans has been severely depleted through all kinds of human activities, including overfishing, chemical pollution, noise pollution and marine debris. Additional pressure is added by the chronic environmental problem of our time, climate change. Climate change doesn’t only magnify the negative effects of other existent threats, it also accounts for several physical and chemical changes in our oceans including an increase in ocean surface temperature, ocean acidification and sea level rise.

While we now understand what causes climate change, we are still in the process of understanding the compexity of its effects. Of course such changes will have a formidable effect on marine life and that also includes cetaceans. What is immediately visible during sightings with marine mammals, like the ones we experienced today, is how intelligent and social they are. These two traits can make cetaceans, particularly toothed whales, more resilient to some environmental issues than other marine creatures but it certainly doesn’t make them immune to them.

Recently local scientists released a paper where they tested the vulnerability of seven cetacean species visiting Madeira to climate change. They did this by developing a model that should estimate how the different species may react to the anticipated changes in climate. The model was plotted according to various „sensitivity factors“ that included diet diversity, population size, genetic variation and geographic distribution of the species amongst others. The test showed that cetaceans with a strict diet, such as Sperm whales (Physeter macrocephalus) or endangered migratory species, such as the Fin whale (Balaenoptera physalus) are highly vulnerable. In contrast, Short-beaked common dolphins and Atlantic spotted dolphins (Stenella frontalis) were shown to be less vulnerable due to their population sizes in the Atlantic and variation in their diets. Island-associated Bottlenose dolphins and Short-finned pilot whales also showed lower vulnerability due to them being highly mobile animals who migrate opportunistically around the Macaronesian archipelagos.

While such papers help us strategically direct conservation efforts at certain species around Madeira, they are based on what we know to date about cetaceans and climate change. Speaking frankly, there are still voids in our understanding of how climate change will affect life on our planet because it is such a multifaceted problem. One thing’s for sure; climate change is a threatening reality and we can still be grateful to encounter marine predators like cetaceans in the wild who are, evidently, just as vulnerable to it as we are.

By Paula Thake

Sightings of the day

Stenella

10:00 Bottlenose dolphins, Short-beaked common dolphins, Short-finned pilot whales