Child Care Is Expensive for Sea Otter Mothers

A sea otter resting in Elkhorn Slough, CA. Credit: Hanae Armitage


By Cody Sullivan
BU News Service

Raising a child is expensive, but few species have it worse than the sea otter. Sea otter mothers nearly double their daily energy costs by the time their pup is weaned, according to a team of scientists at the University of California Santa Cruz. Sea otters already lose significant amounts of heat to their cold, Californian, watery environment. But adding child care to that energy loss can leave a sea otter mother with an energy bill that is sometimes too high to overcome.

A study done by a team of researchers, led by Nicole Thometz, measured the amount of energy that sea otter pups demand. They found that upon birth of a pup, sea otter mothers face a 17% increase in their daily energy budget, then by the time the pup is completely weaned–six months later–it jumps to a 96% increase. The findings were published in the June 2014 edition of the Journal of Experimental Biology.

In addition to lactating a sea otter mother has to spend extra time foraging to support both herself and a pup. Older pups can actually require more milk from their mother and more energy despite being able to forage for themselves, because pups have higher activity levels.

Otters reproduce every year. If a mother is already in poor condition when giving birth, she will sometimes abandon her pup early on. “There is an initial two week window [after birth] that is most important for a mother in determining if she will keep a pup,” says Thometz. A female may abandon a pup to preserve her own health for the next breeding season, when she might be more successful.

Poor body condition can result in a potentially deadly syndrome named “end lactation syndrome” that affects a mother after weaning her pup – a combination of symptoms including nutritional deficiency, generally poor health, and an increase in susceptibility to disease. Scientists have noted an increase in end lactation syndrome, female strandings, and mortalities over the last twenty years. Experts think the problems might result from more competition for resources as the otter populations have increased in their central range of Big Sur and Monterey Bay. Interestingly, otter populations on the fringe of this range do not face the same rise in end lactation syndrome. They still haven’t recovered from when the fur trade decimated their populations throughout the 1800s.

Thometz plans to quantify the cost of lactation to further understand why sea otter mothers experience such hardship when raising pups. While a reproductive strategy that can result in a mother’s death or pup abandonment may seem overly expensive, it is not uncommon for strange behaviors to evolve. As Thometz says, “Evolution does not always produce the most effective process.”

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