The hunt is on- Adaptations of the Weddell seal
The Weddell Seal (Leptonychotes weddellii) is an abundant, non threatened species of seal and is one of the six species of seal that live in Antarctica, and amongst the four which are are specialists in ice-habitats. This seal has captured the imagination of many people with its large eyes and its chubby ‘bean-bag’ like body, but under the water they are one of the most efficient predators within the extreme environment of Antarctica.
It is the most southern dwelling mammal and inhabits coastal circumpolar fast ice, which exposes it to air temperatures of -10 to -60°C, and sea water temperatures around -1.8°C. Due to feeding beneath the ice, its diet comprises mostly of fish, prawns and octopus.
To feed in the water under the ice, this Seal has developed specific adaptations which allow it to access, see and capture its prey efficiently in order to survive.
Diving and Gnawing…far from boring
With a streamlined body, the Seal is able to manoeuvre through the water and its thermally efficient skin and blubber layer make it a highly effective diving predator. Submersion can often extend for up to 80 minutes on a single breath, allowing hunt distances as far as 5km from a ‘breathing hole’. Even with dive times less than 25 minutes, the Seal is capable of diving between 100 and 350m with record depths around 700m.
A ‘breathing hole’ is a crack in the ice which enables the Seal to haul out on the ice whilst having access the water below to hunt. These cracks are essential to these Seals as they facilitate their survival on the ice year round. During the warmer months, these cracks are more readily available, however, when the temperatures drop in the winter time, the holes freeze over. The Weddell seal then maintains the hole using its teeth. To do this, the seal opens its mouth and moves its head from side to side relatively vigorously. This method has a negative effect on the teeth and life of the seal and studies suggest that the condition of the teeth is correlated to the mortality of the adult Weddell seal.
A video of the ‘sawing action’ using teeth to maintain breathing holes
Sourced from: jessiefudge13
In order to hunt in low light conditions with an exposure to snow, wind and cold water, it has specially adapted eyes.
To protect the eyes against the ‘elements’ and salt of the water, it has a nictitating membrane. This membrane is similar to that of our domestic mammals but is more fundamental for the survival of the Seal due to its reliance on its vision for food intake.
At the back of the Seals eye, it has a tapetum layer which is identifiable as the glow you may see in a cats eyes during dim lighting. This layer aids the vision of the Seal during deep dives and in dim lighting which is most prevalent during the austral winter.
The bubbles the bubbles!!
-Once below the ice, the challenges of low lighting have been…
-are they using valuable air to do so? is this happening near air holes so can go back up for air?