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Weddell seal moms sacrifice diving capacity to provide iron to pups; climate change could add vulnerability

Weddell seal mothers sacrifice their diving capacity to provide their pups with iron: Climate change could make seals more vulnerable

A female Weddell seal lies on the ice with her pup in Antarctica. A new WHOI-led study shows that female Weddell seals provide so much iron to their pups during lactation that the mothers have to drastically limit their own diving and foraging opportunities underwater. (All images are made under license NMFS 17411-03). Credit: Michelle Shero/Woods Hole Oceanographic Institution

Weddell seals are excellent divers and give their pups so much iron during lactation that the mothers drastically limit their own diving and foraging opportunities underwater.

This is according to a new paper, “Iron Mobilization During Lactation Reduces Oxygen Storage in a Diving Mammal,” published in nature communication.

“Discharge 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 a shorter dive duration after weaning than breeders who skip,” the paper states, citing non-breeding seals used as controls in the study. “High iron requirements during lactation ultimately affect the diving capacity as reproduction costs in marine mammals.”

Seals have a much higher iron load than land mammals because the seals need that protein to carry oxygen in their bodies, said Michelle Shero, assistant scientist in the Woods Hole Oceanographic Institution (WHOI) Division of Biology and lead author of the paper. “That basically acts like an internal dive tank for those animals that allow them to dive for so long,” Shero says. “The females essentially transfer their diving abilities to the pups when they’re nursing, through this transfer of iron. Nobody’s looked at that before.”

Weddell seal mothers sacrifice their diving capacity to provide their pups with iron: Climate change could make seals more vulnerable

A collaborative team in Antarctica works with a Weddell seal on a windy day. The team recently found that female Weddell seals sacrifice their diving capacity to provide their pups with iron. In the background is a flue from Mount Erebus, the world’s southernmost active volcano (all photos were taken under permit NMFS 17411-03). Credit: Michelle Shero/Woods Hole Oceanographic Institution

Based on the average iron concentrations in the milk determined in the study, a female seal transfers 309-614 milligrams of iron per day to her pup. “This is an exceptional transfer rate compared to land mammals,” the paper said, noting that the rate is 8-15 times greater than doses exceeding the daily upper limits and results in iron toxicity to humans despite a relatively similar body size between an adult human and an adult. a nursing Weddell seal pup.

Weddell seals are exceptional divers, routinely diving and foraging underwater for 20 minutes at a time, with the longest recorded dive at 96 minutes. However, when the seals nurse, they supply their pups with a tremendous amount of iron, which the mothers would normally use to maintain high hemoprotein levels in the tissue to carry oxygen for those dives, the study notes.

Postpartum dive times in women decreased, and late summer dives were the shortest compared to the rest of the year, according to the study.

The article notes that reduced physiological diving capacity would typically be detrimental to a seal’s body mass recovery and fat storage after weaning. In Weddell seals, the effects of reduced aerobic diving capabilities “can be mitigated if they are closely linked to the seasonal pulse of productivity in the Antarctic environment at high latitudes,” the paper states. “The fact that postpartum women gained mass during the late summer period, despite their shorter diving duration, indicates that they were not too adversely affected by reduced diving capacity after weaning.”

Weddell seal mothers sacrifice their diving capacity to provide their pups with iron: Climate change could make seals more vulnerable

Study lead author Michelle Shero next to a Weddell seal. Credit: Skyla Walcott

However, the paper warns that “the precise temporal alignment of diminished diving potential with the seasonal productivity pulse may make this species more vulnerable to shifts in the climate regime that would decouple these events.”

“It’s quite striking that the females wean their pups during this time when there’s a lot more productivity, and when that productivity seems to be shallower in the water column,” said study co-author Jennifer Burns, professor and chair of the Biological Sciences Department. the Texas Tech University. “The female seals’ diving abilities are limited, but they may not have to work as hard to catch prey anyway. Similarly, although their pups have a lower diving capacity than their mothers, weaning during a period of high productivity can help their foraging. But if the timing of the productivity pulse were to change, the seals probably wouldn’t be able to forage as successfully.”

Shero adds that “if the environment changes in the long term such that the seals have to start catching fish with low iron content, that will affect the iron physiology of the seals, how much they can store in their bodies over this long period of time.” .” dive, and how much they can give to their pups.”

Shero, who has been studying Weddell seals in Antarctica since 2011, says it has been “a privilege” to work with this iconic species.

“I would like this study to help open up the field of iron physiology and how it affects the seals’ ability to dive and raise their young,” Shero says. “I think there’s just a lot more to it than just looking at how many fish the seals can catch when we’re trying to assess animal health.” She says iron dynamics should also be considered when managing seal conservation. Burns echoes this sentiment, saying that “certain types of prey may be more important than previously recognized, especially during certain times of the year, such as just before delivery and just after weaning, when iron intake can be critical for both mothers and their mothers.” puppies.”


Young Weddell Seals Need to Practice Navigating Before Hunting


More information:
Michelle R. Shero et al, Iron mobilization during lactation reduces oxygen storage in a diving mammal, nature communication (2022). DOI: 10.1038/s41467-022-31863-7

Provided by Woods Hole Oceanographic Institution


Quote: Weddell seal mothers sacrifice diving capacity to provide the pups with iron; Climate Change May Add Vulnerability (2022, Aug 2), retrieved Aug 2, 2022 from https://phys.org/news/2022-08-weddell-moms-sacrifice-capacity-iron.html

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