Fur seal fertility: could a pathogen be impacting Australian fur seal pup production?

Crawling through seal poo on a remote Bass Strait island and wrestling a gull for the fresh placenta of an Australian fur seal (Arctocephalus pusillus doriferus) is just a regular day in the office for Brett Gardner.

He puts himself through this to find out what’s ailing these majestic marine mammals.

Australian fur seals have been showing signs of distress over recent decades, with reduced rates of pup production threatening their population. (Although a study published last week suggests that climate change may help the fertility of seals of Kanowna Island, just south of Wilsons Promontory, Victoria.)

Gardner, a PhD Candidate with the University of Melbourne, is investigating how disease may be impacting their capacity to bear pups to term.

Exactly why fur seals are struggling to produce and raise large numbers of pups has been hard for researchers to pin down, but the impact of pathogens on the species’ fertility and abortion rate had not been investigated.

“That’s where I came in, I decided, well, I’ll have a look and see if any of the common causes of abortion that we would look for in terrestrial mammals are present,” Gardner says.

Pernicious pathogen found

By analysing the aborted foetuses and placentas of Australian fur seals on Bass Strait islands Gardner found that the pathogen Coxiella burnetii was present in seal populations. This finding was recently published in Frontiers of Marine Science.

On land Coxiella infects animals such as goats and cows, often causing abortion and birth defects. When humans breathe in dust contaminated with Coxiella it can cause Q fever, which can be deadly.

“The only reports prior to this of Coxiella [in marine mammals] was in the northern hemisphere, but it’s been associated with declining populations of marine mammals in the northern hemisphere,” Gardner says.

It struck him as significant that the pathogen was found in both aborted foetuses and placentas of pups who’d been born alive.

“Either they’re producing pups preterm and they’re pretty weak and might have a decreased survivability,” he says. “Or it could be that the Coxiella is there and it’s not a pathogen like it is in terrestrial mammals.”

The Coxiella infecting these seals was subtly different to its terrestrial counterpart.

“A lot of the markers that we were looking for don’t get expressed in the marine species,” Gardner says. “So, a very good question is, is this a major cause of their population declining or is this actually some organism that they’ve always had around?”

A smoking gun?

Seal expert Mary-Anne Lea, Professor in Ecology and Biodiversity at the Institute for Marine and Antarctic Studies (IMAS) in Hobart, agrees that unpicking the causes of faltering pup production is incredibly complex. Lea was not involved in the study.

Even in species such as the Steller sea lion (Eumetopias jubatus), a well-studied struggling northern hemisphere species that has been known to carry Coxiella, it’s hard to determine if the presence of the pathogen is a cause of the population decline.

Shifts in the prey base (food availability), pollutants, anthropogenic interaction such as bycatch, climate change, increased marine heat waves and extreme weather events such as storm surges could all be impacting pup production of Australian fur seals, Lea says.

“If there are unseasonal storm surges that wash pups off the island then that can have a direct impact on mortality.”

Another possibility is that a combination of stressors in the system may lead to “conditions ripe for the expression of those pathogens”, she explains.

“Without regular screening and also population monitoring, where you’re studying known individuals and you get a sense of how frequent these events [abortions] are for individuals, it’s really hard to attribute an impact,” Lea says.

Gardner is up for the challenge of figuring out just what the impact of Coxiella might be on pup production: “That’s going to be way more complicated because I’ll have to go and capture females, determine if they’re pregnant then determine if they have Coxiella and then see if they produce a pup to term.”

Could this bacteria impact humans?

Because the Coxiella brewing in seals is subtly different from the one we are used to on land, it’s not known whether it could jump across into humans and cause Q fever.

“We really desperately need to find out if this is actually a very risky pathogen or if it lacks the massive virulence of terrestrial Coxiella,” Gardner says.

Given Gardner’s penchant for crawling through seal colonies, this is more than an academic question for him; it’s personal: “There’s a lot of people working in seal colonies around Australia and New Zealand and we’re all crawling through the dust, which is where these Coxiella sit in their environmentally resistant form.” Lea, in turn, emphasises the link between human health and ecosystem health. “Humans are part of these ecosystems and we affect them and are affected by them,” she says.