by Bryan Jáuregui for the Journal del Pacifico
Swimming with the sea lion puppies at Los Islotes, the southernmost rookery of the California Sea Lion, Zalophus californianus, is truly one of
by Bryan Jáuregui for the Journal del Pacifico
Swimming with the sea lion puppies at Los Islotes, the southernmost rookery of the California Sea Lion, Zalophus californianus, is truly one of life’s great joys. The puppies are often playful and naughty, nibbling on the flippers and fingers of human visitors, while their teenage siblings like to sidle up to humans for a good belly rub or game of chase. Their mothers may be found sunning themselves on the rocks, enjoying a snooze, while the males who rule the 20 territories of Los Islotes indefatigably patrol the waters to ensure everyone’s safety. It is a scene of utter Baja bliss, and humans can’t help but feel a magical glow from this most wondrous of wildlife encounters.
All of which begs the obvious question: Why are the males working so hard when everyone else is just having a good time?
Claudia J. Hernandez-Camacho, a professor of biology at CICIMAR in La Paz, has been studying the sea lions of Los Islotes and the Sea of Cortez since 1990. In particular, she has studied the entire lifespan of 190 sea lion individuals (94 females, 96 males) who were hot-branded by her professor between 1980 and 1984. Her findings, based on these specific sea lions and others, tell a complicated tale for our pinniped friends.
“Sea lions are polygynous, meaning that one male mates with several females in the territory that he defends on land and sea. It takes an enormous amount of energy to defend this territory, and in the breeding season a territorial male, who is so focused on his job that he barely eats or sleeps, can lose up to 30% of his impressive body weight (400 to 500 kilos, or about a ton) in just a few weeks.”
One would assume, of course, that the males are spending this incredible amount of energy to defend their harems and offspring, to ensure the survival of their genes. “But this is not exactly the case” says Claudia, “they are defending the territory, not the females.” The science proves this out. “Genetic studies show that just 15% of territorial males are the fathers of the newborns the next breeding season. It is not just that the females hook up with and get impregnated by wandering, opportunistic males when they slip off for their 4-5 day feeding trips, which they do, but in some cases the territorial males are not even copulating with the females in their territory.” All that work and no sex?
“It’s a little more complicated than that,” says Claudia. “There are 600 individual sea lions at Los Islotes, and every year around 170 pups are born. Almost 30% of the pups die in the first two years, either from disease or because they or their mothers have fallen prey to predators. But that means that 70% are surviving. With this type of situation, many of the sea lions are, by definition, related. It could be argued that the Los Isl