When you think about the Galapagos Islands, there are a few things that come to mind. There’s Charles Darwin, of course, and the studies he made there that contributed to his development of the idea of evolution. And the amazing wildlife, including tortoises and iguanas and a whole host of birds. What you don’t think of are things like pollution and invasive species, but these are growing problems, especially in the areas inhabited by humans.
Some islands are still pristine, though, and that gave a group of biologists, led by the Zoological Society of London, a chance to see how one species, the Galapagos sea lion, is affected by the presence of humans. The researchers compared immune activity and body condition of two populations, one in Bahia Paraiso on the undeveloped island of Santa Fe and another that lives in the center of the rapidly growing town of Puerto Bazquierizo Moreno on San Cristobal. The study was published last week in PLOS One.
None of the animals appeared to have signs that they were sick, but those that lived in town had more active immune systems. And among the pups in that colony, those that had higher levels of antibodies had thinner skinfolds and were skinnier.
“A tell-tale sign of an unhealthy sea lion is a thinner than normal layer of blubber, which is what we saw in the sea lions on San Cristobal,” study coauthor Paddy Brock of the ZSL said in a statement. The more active immune systems could indicate “a threat of infectious disease, which could mean human activity is increasing the chance of potentially dangerous diseases emerging in the Galapagos sea lion,” Brock said.
Puerto Bazquierizo Moreno does not seem like it would be a great place to be a sea lion. The bay is home to more than 200 boats and filled with fecal contamination from the vessels and sewage from the town. And the land has a bunch of animal threats, including people’s pets, feral cats and rats. If these factors are impairing the immune systems of the sea lions that live in the area, the impaired immunity could reduce the marine mammals’ ability to hunt, the researchers say.
And the Galapagos sea lions don’t need anything else to hamper their survival. The species was listed as endangered by the IUCN after its already-small population declined by more than 50 percent in the last three decades. The sea lions, which are a bit smaller than the more familiar California species, are not afraid of humans and like to hang out on rocky shorelines and sandy beaches (above). That can put them in direct contact with the human population and make them vulnerable to threats like uncontrolled dogs that will kill sea lion pups.
These sea lions have figured out ways to deal with some threats — they’ve been known to mob Galapagos sharks that approach their rookeries — but they haven’t yet evolved to deal with the ones humans have brought to them. Their immune systems didn’t evolve to exist in a sewage-filled, pet-dominated environment. And it appears that’s put them at even more risk of disappearing from the planet.
Image credit: ZSL_Paddy Brock, via EurekAlert