19.02.2019 – Visibility matters

A placid ocean is always ideal for Whale-Watching trips as it makes finding the animals much easier for both our spotter and our crew on the ocean. The calm ocean conditions also emphasise how crystal clear the waters around the archipelago truly are, allowing us to fully appreciate the animals approaching our boats. Apart from benefiting fishermen, whale-watchers, divers and snorkelers, it also grants the animals frequenting the waters of Madeira a couple of advantages.

As an oceanic island, Madeira is an ideal pitstop for several underwater predators who feed in its deep waters whilst enjoying the shelter of its coastline. Cetaceans come here to socialize, rest and feed on the abundant prey both at the surface and in deeper waters. Most people know that cetaceans primarily rely on their acoustics to investigate their environment by generating soundwaves in their nasal passages which are further modified as biosonar in their melon, directed and modified according to their needs. While vision is generally rather secondary with cetaceans, it plays a very important role when inspecting their surroundings at the surface. This is facilitated by the highly-adaptive, mobile lens in their eyes which provides them with good vision below and above the surface.

Bottlenose dolphins (Tursiops truncatus), for instance, are particularly curious and often approach our boats to ride the waves at our bow or surf the waves at the rear generated by our zodiacs strong engines. While doing so, the animals often glance up at us or leap alongside our boat, inspecting their admirers at the surface. The Short-finned pilot whales (Globicephala macrorhynchus) were less inclined to check us out and more preoccupied with relaxing at the waters surface. As deep-diving, nocturnal predators, pilots have little need for eyesight in the dark ocean where they hunt for squid and rely entirely on their biosonar during such pursuits. Most of their daytime activites however, such as socializing or resting, occur at the surface making vision a useful tool. While their biosonar is still being used to scan their environment, using their eyes means allows them to invest more energy in generated soundwaves for communication rather than orientation.

In between the dynamic Bottlenose dolphins and the lethargic Pilot whales we also saw two Loggerhead turtles (Caretta caretta) basking at the surface. Apart from their incredible sense of smell, sea turtles also use their eyesight to forage for prey so visiblity definitely matters for these reptiles. Above the waterline things aren’t so sharp; turtles are extremely short-sighted in air making them often dive down again in fright when they see a boat approaching.

By Paula Thake

Sightings of the day

Stenella

10:00 Bottlenose dolphins, Short-finned pilot whales, Loggerhead turtle