It’s not easy being a sea otter mom. Mothers exert twice as much energy as females without offspring, according to a study published online today in The Journal of Experimental Biology. Ecologists began studying the animals when they noticed more and more mama otters dying and in bad shape with thinner bodies. After observing young southern sea otters in their natural habitat and in aquariums, the team calculated the daily energy invested between birth and 6 months, when weaning begins. The researchers found that as Enhydra lutris nereis (pictured above), an otter that lives off the coast of central California, grow more and more, exertion on mom’s part increases—by the end of lactation, daily energy usage skyrockets by 96% from prepregnancy levels. Weary moms often can’t eat enough to meet the demand, leading to substantial weight loss, weak immune systems, and even death. The findings suggest that southern sea otters may be faced with some tough decisions when raising their young, like whether to abandon pups early on to save energy (and their own lives).