The Weddell seal can stay under water for an extremely long time. 96 minutes is the longest dive ever measured, on average it is about 20 minutes. In search of fish, they dive up to 600 meters deep, sometimes covering more than ten kilometers. In order for the Antarctic marine mammals not to run out of air, they need very special physical conditions.
Seals can store much more oxygen than land mammals or humans. In relation to their body weight, a lot of blood flows through their veins, it makes up a good fifth of their body mass, in land mammals it is only seven percent. There is a lot of iron in the blood and muscles, which can bind oxygen. In addition, the vital oxygen is consumed very sparingly.
Nursing costs substance
Like the researchers around Michelle Shero now report from the University of Alaska, the prerequisites for the diving skills are placed in the cradle of the seals. Compared to others The dog seal Weddell seals nurse their young for a relatively long time, namely six to seven weeks. In doing so, they use up a lot of their own reserves, and the females lose between 100 and 150 kilograms of body weight. However, as with other mammals, breast milk not only contains calories, but also many micronutrients such as iron.
This is shown by the study that has now been published in the specialist magazine “Nature Communications”. Study, for which Shero’s team analyzed the blood and breast milk of mother seals from 2010 to 2017 and compared them to females who had no offspring that season. Weddell seals only give birth every other year. In addition, the behavior of the animals was observed throughout the southern summer.
Iron-rich breast milk
According to the study authors, more free iron circulates in the blood of new mothers than in the other females. Apparently, stored iron is mobilized to be passed on to offspring. This is how the micronutrient also gets into breast milk. This actually contains enormous amounts of iron, a hundred times as much as in land mammals. Such levels of the highly reactive element would be toxic and dangerous to humans and other mammals. It is unclear why they are apparently harmless to the seals.
In any case, iron loss is not without consequences for the mothers. According to the researchers, the amounts stored have shrunk significantly at the end of the summer. This is also reflected in the shorter dives. On average, the mothers hunt five minutes less than the other females at the end of the season. Instead, they go hunting more often, presumably to compensate for the loss of substance through suckling and to replenish the iron stores.
According to Shero and Co., the offspring, on the other hand, benefit from the iron in breast milk. When the young Weddell seals start hunting themselves, they can stay underwater longer and become more self-sufficient. This can possibly ensure their survival. About half of all seal pups die in their first year.
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