Sea turtles… in Alaska?
During 2022 Sea Turtle Week this article written by NOAA Fisheries Alaska Regional Office caught our attention. Sea turtles in Alaska? Is it not too cold there, in the far North?
Yes, it is very cold in Alaskan waters, even in the Southernmost part of the state. Sea water temperature records in Anchorage show that the sea can reach -1°C in winter, far too low for sea turtles. However, in the warmer summer months, it can rise up to 14°C.
Sea turtles are reptiles, and are not able to regulate their body temperature like birds or mammals. They depend on the ambient temperature, and for that reason they tend to live in temperate to tropical waters. In general, sea turtles cannot survive temperatures below 10°C, except for the incredible leatherback sea turtle. This species is not just the largest of sea turtles, and the best adapted to diving, but is also able to “regulate” its body temperature to some extent, keeping it over 10°C higher than the ambient water temperature when needed. This species has been reported swimming around ice floes at sub-arctic latitudes. How do they do this?
To begin with, a large body size allows to maintain a higher body temperature, even while resting. Large sea turtles have high internal heat storage capacities, which means that they can keep their body warm for a while once they have managed to increase the body temperature (through basking or swimming, for example).
Being active (swimming and diving) obviously helps increase body temperature. In fact, green turtles (the other sea turtle species most sighted in Alaskan waters, together with leatherbacks) can significantly increase their body temperature in relation to surrounding water temperature through their swimming activity: they can raise their metabolism 10 times above standard metabolism when active.
But leatherbacks also have a thick adipose tissue layer (6-7cm) with brown fat, which reduces the heat exchange with the surrounding water even further. And above all, they are able to adjust the blood flow from the body core to the skin and flippers in order to better regulate body temperature: this allows them to keep warm in colder waters, and to not overheat while swimming in warm tropical waters.
So, if you are planning a trip to Alaska or Newfoundland, maybe you should add the sea turtle in your to-see list of wildlife?
If you are interested in this subject, have a look at Wallace & Jones, 2008 “What makes marine turtles go: a review of metabolic rates and their consequences”, in the Journal of Experimental Marine Biology and Ecology 356.