Weddell seals sacrifice large amounts of energy for their pups

Today’s Video of the Day from the National Science Foundation describes the sacrifices made by Weddell seal moms for their offspring. A recent study led by the Woods Hole Oceanographic Institution revealed that Weddell seals give so much iron to their pups during lactation that they dramatically limit the energy they have left over for diving and foraging. 

“Offload of large amounts of iron hinders female Weddell seals’ ability to maintain their own endogenous heme (hemoglobin and myoglobin) stores, and post-partum females have shorter dive durations following weaning than skip-breeders,” wrote the study authors. “High iron demand during lactation ultimately impacts dive capacity as a cost of reproduction in marine mammals.”

Study lead author Michelle Shero explained that seals have much greater iron loads than terrestrial mammals because the seals need those proteins to carry oxygen in their bodies.

“That basically acts as a sort of internal scuba tank for those animals that allows them to dive for so long,” said Shero. “The females are essentially transferring their dive capacities to the pups when they nurse, through this transfer of iron. No one has looked at that before.”

The experts determined that a female seal transfers 309 to 614 milligrams of iron per day to her pup. “This is an exceptional rate of transfer relative to terrestrial mammals,” wrote the researchers.

Weddell seals are incredible divers. They routinely dive and hunt for food underwater for 20 minutes at a time. The longest recorded dive by a Weddell seal was 96 minutes. When the mothers are lactating, however, they are giving up the hemoprotein levels they need to carry oxygen for long dives.

Video Credit: National Science Foundation 

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By Chrissy Sexton, Earth.com Editor

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