09.09.2020 – Sustainable stocks

The overcast skies over Calheta gave the ocean a steel-like glare as we set off on our Stenella for this mornings tour. We were heading for the waters far outside Paul do Mar, a haven for dolphins foraging for prey. Deep currents often well up to the surface at the edge of the plateau 3 nautical miles off the coast, leading to gatherings of schooling fish and we often encounter small species of dolphins hunting or travelling around these waters.  Surely enough, our spotter managed to locate a group of Atlantic spotted dolphins (Stenella frontalis) in the area, charismatic creatures that, judging by their will to interact, had probably just indulged on some of the available prey. Like most dolphins, the spotted don’t just resort to schooling fish but also occasionally dive to hunt squid which are also abundant in Madeira’s deep waters.

Major shifts in fish stocks, largely caused by overfishing and climate change, have enabled fast-growing organisms such a squid to proliferate in our oceans. Madeira is generally considered as an ideal habitat for squid populations, prompting several species of beaked whales and other deep-diving toothed whales to forage in her depths. While squid forms part of an important prey spectrum for dolphins since it’s a very hydrating meal, it requires the animals to dive deeper and lacks some of the nutrients that the animals need from specific fish species.

The Bottlenose dolphins (Tursiops truncatus) we met outside the waters of Calheta were in the process of foraging in deeper waters, engaging in several dives in the area and paying little attention to us. While the species is known to dive beyond 500m for a good meal, these animals were probably feeding on larger fish like Dolphinfish (Coryphaena hippurus) judging by the shiny silvery scales floating below our boat in the water column.

Being the adaptive creatures that they are, dolphins can help regulate an imbalance in our oceans food webs by feeding on what’s in stock. They cannot, however, balance the entire ocean ecosystem which is why fishing must be regulated and consumers must make sensible choices with their fish. If we do not harvest our oceans sustainably , fish stocks will collapse and so will the populations of predators that depend on them.

By Paula Thake

Sightings of the day

Stenella

10:00 Atlantic spotted dolphins, Bottlenose dolphins