Endangered sea lions' fate may be sealed by humans

Galapagos sea lions
If urbanisation on the Galápagos continues at its current rate, the subtle effects documented in our two publications could become more acute, and begin to have knock-on effects on mortality and reproduction.
Dr Paddy Brock
Scientists working at the Zoological Society of London have highlighted the threats posed to endangered Galápagos sea lions due to human activity…

A paper from researchers at the Zoological Society of London (ZSL) which appeared recently in the open access journal PLOS ONE has found that human influences on the environment of the Galápagos sea lion (Zalophus wollebaeki) are comprising the animals’ immune systems and could even jeopardise the survival of the species.

The Galápagos sea lion is listed as endangered (EN) by the International Union for Conservation of Nature (IUCN), with a small, fluctuating population size which, it has been suggested, has declined by as much as 50 per cent over the last 30 years. The species faces the dual threat of an unpredictable food supply and infectious disease.

First author Dr Paddy Brock, who completed his PhD at ZSL’s Institute of Zoology and the University of Leeds, shared his expertise and thoughts on the findings with ScienceOmega.com.

He and his colleagues spent more than 18 months in the Galápagos archipelago, tagging 60 sea lions on the island of San Cristóbal and the same number on Santa Fe. Whereas San Cristóbal is inhabited by humans and the attendant pets and pests, the island of Santa Fe has no resident humans, dogs, cats, rats or mice.

Compare and contrast
 

To get an idea of the effect that the presence of these other species has on the wellbeing of the sea lion communities, the team monitored the physiology and behaviour of the animals they tagged in order to compare the two populations. In doing so, they took various factors into account.

"In our overall study design and in the PLOS ONE analysis we took into account the age and sex of sea lions, as well as the period over which the changes in immune activity and body condition occurred," said Dr Brock. "We also statistically controlled for multiple captures of the same individual juveniles.

"The PLOS ONE analysis sits in the context of our previous paper, which described immune activity in the Galápagos sea lion in a broader way and discusses the possible influence of potentially relevant biological and environmental factors on Galápagos sea lion immune activity."

Thinner than normal layers of blubber – a telltale sign of an unhealthy sea lion – were observed in those individuals from San Cristóbal; the previous paper Dr Brock mentioned also discusses the magnitude of the difference in immune activity between the two colonies.

"What are likely to be adult levels of total immunoglobulin G (IgG) – which is a measure of antibody concentration – were approximately 30 per cent higher in sea lions from San Cristóbal than in sea lions from Santa Fe," he clarified.

A combination of factors
 

The fact that the immune systems of the San Cristóbal sea lions were more active than those of their cousins on Santa Fe, suggests that their risk of infectious disease is higher, the conservationists believe, possibly as a result of their proximity to humans.

Paddy Brock sea lions
Dr Brock pictured with Galápagos sea lions
Despite the existence of laws intended to protect the unique flora and fauna of the Galápagos, pets are regularly imported, increasing the risk of novel infectious diseases being introduced to the islands. According to the IUCN, contact between sea lions and both feral and domestic dogs ‘presents the greatest danger of disease transmission’.

Combined with the dumping of sewage into San Cristóbal’s bay and the effects of climate events on their food supply, it is not surprising that the future of the Galápagos sea lion may at times appear bleak. Investment of their bodily resources in immunity can result in the animals being less likely to hunt and therefore more likely to starve when food supplies are short.

"If urbanisation on the Galápagos continues at its current rate, the subtle effects documented in our two publications could become more acute, and begin to have knock-on effects on mortality and reproduction," Dr Brock commented. "In other words, they could contribute to a population decline which, if combined with unfavourable environmental conditions, could see sea lion numbers crash dramatically."

The best interventions
 

Dr Brock explained that there are measures which could be taken now to mitigate the negative impacts that have so far been documented.

"The Galápagos authorities should aim to enforce controls on the import and breeding of pets, develop more sustainable waste management systems and work to increase the effectiveness of the collaboration between the Galápagos National Park and the Galápagos municipal authorities," he said.

"They could also work to legalise pet vaccination – and thereby make possible the beginning of a representative veterinary register – on the islands, and develop a zoning programme for beaches in towns to minimise contact between wild and domesticated animals."

Further research is planned by the ZSL and their collaborators into the threats faced by the Galápagos sea lion, as Dr Brock outlined.

"We are currently developing mathematical simulation models of disease spread in domestic animals and sea lions on the Galápagos. These will allow us to predict which combination of interventions may best reduce disease risk to the Galápagos sea lion, and the results will be easily translatable into applicable conservation strategy by the Galápagos National Park."


Read the full text of the article, Immune Activity, Body Condition and Human-Associated Environmental Impacts in a Wild Marine Mammal...

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