Male elephant seal colonies are reportedly dying earlier than usual as they have to keep large herds that sometimes number up to 100 females happy.
A study of about 14,000 southern elephant seals in the Macquarie Islands in the southwest Pacific found that the survival rate of male and female seals is the same at an early age, but that of males drops sharply after about eight years of life.
The survival rate of men dropped by about 50%, while that of women remained constant at 80%.
Adult males weigh about five times more than females, says, among others, the study published in the journal Royal Society Open Science.
Study author Sophia Volzke of the University of Tasmania wrote that fatter male seals had significant reproductive advantages.
“They only get their food from the ocean. While when they stop on the ground (to reproduce) they compete with other males for access to females”.
“Seals must have fat reserves to survive on land, sometimes without eating anything for weeks or even months.”
But she added that the species exhibits some cases of “extreme polygyny” where a small number of the most dominant and largest males control the herd as a kind of harem for breeding females.
“A few larger males start to control the harem and only when it gets too big do they allow other males to become their breeding assistants,” she says.
“It depends on the size of the harem and the geography of the beach, for example if there is a very long beach they are more likely to create several herds in the form of a harem.”
Researchers say that dominant males gain weight rapidly to compete and this may reduce their chances of survival.
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