Human Influences Endangering Galapagos Sea Lions
July 1, 2013

Human Influence Endangers Galapagos Sea Lions

Brett Smith for - Your Universe Online

Like all biological functions, the immune system places demands on an organism and a new study in the journal PLoS ONE has found the highly active immune systems of some endangered Galapagos sea lions are stressing the animals to the point of starvation.

In the study, the researchers compared two sea lion populations living within the archipelago: those near the human populated Islands of San Cristobal and those living by the unpopulated Santa Fe. The team observed sea lions living near humans as being more physically drained by their immune systems -- leaving less energy to hunt for food.

The study researchers from the Zoological Society of London (ZSL) pegged this difference in sea lion health on the activities of humans and their introduction of foreign species to the islands.

"The immune systems of San Cristobal sea lions were more active, perhaps indicating a threat of infectious disease, which could mean human activity is increasing the chance of potentially dangerous diseases emerging in the Galapagos sea lion," said ZSL researcher and study co-author Paddy Brock.

"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," Brock said. "This was all the more notable as we didn't notice these patterns in sea lions on Santa Fe, where they live without the presence of people or pets."

Over the course of more than 18 months, the research team tagged and monitored 60 Galapagos sea lions. Looking for three previously described immune response measures, the researchers took repeated blood samples from "pups" that were 3-months-old and younger; and "juveniles," considered 6-months-old and older. The blood samples were processed so that the scientists could analyze the levels of these distinct biomarkers for immune system health.

The team also recorded three different measures of sea lions' body condition. These measures were used to assess each animal’s health with respect to resource availability.

After analyzing their data, the team came to two main conclusions: immune systems health is directly linked to body condition and sea lions living on the populated islands were more likely to have poorer health with respect to both measures.

Those findings led the team to conclude higher levels of pathogens near human populations are placing a greater cost on the immune systems of sea lions -- affecting overall body health.

"We are increasingly aware of the threats of infectious diseases to wildlife around the world, from amphibians in the tropics to the birds in British gardens," noted ZSL director Tim Blackburn, who was not among the study's co-authors. "It is worrying that we are now potentially seeing such threats to sea lions in the supposedly pristine wilderness of the Galapagos Islands."

In a press release from the ZSL, the organization cited the regular importation of pets to the islands, despite regulations against it. The group said this practice raises the risk of importing new diseases and spreading them to local species.

The conservation organization also mentioned the dumping of sewage around San Cristobal as a source of higher germs and bacteria levels around the islands that could be impacting the sea lions.