Abstract
New Zealand sea lions (Phocarctos hookeri) are an endemic and endangered species. Pup mortality at Enderby Island (50.5°S, 166.28°E) in the New Zealand sub-Antarctic has been well studied, with subsequent investigations yielding more intricate detail of the causes of mortality, as new diagnostic methods become available. Klebsiella pneumoniae was first reported in 2001–02 at this site, causing a pup mortality epizootic and is now known to be present at several colonies. This bacterium is a common mucosal commensal of humans and animals, however the agent found in pups at necropsy is a hypervirulent strain, readily recognised in microbial culture as being hypermucoviscous. Infection causes septicaemia with a common syndrome of subsequent meningitis and polyarthritis. This investigation uses histopathology and microbiology, with new modalities such as matrix assisted laser desorption/ionisation—time of flight mass spectrometry to show that Klebsiella septicaemia could have historically been, and continues to be, the most important cause of pup mortality, but has been previously underrepresented due to the often cryptic presentation and sometimes peracute course of disease. Hypermucoviscous K. pneumoniae should be considered a serious threat to pup survival in the species, causing on average 60.2% of pup deaths annually at Enderby Island between 2013 and 2018, with likely more continuing mortality following pup dispersal and the cessation of the summer monitoring season. Less common causes of death included starvation (14.8%), trauma/asphyxiation (9.9%) and other infections (7%). This study forms the basis for further evaluation of risk factors for pup mortality in the species, with a view to developing active mitigation.
Highlights
The New Zealand (NZ) sea lion (Phocarctos hookeri), the only pinniped endemic to NZ, is rare and highly localised, with almost all breeding occurring in the outlying sub-Antarctic islands between 50-53 ̊S
All dead pups had been born at Sandy Bay, except for 37 confirmed or presumed to originate from nearby Dundas Island (Fig 1B), from where mothers and pups begin to disperse in mid-January
There was a significant correlation (p
Summary
The New Zealand (NZ) sea lion (Phocarctos hookeri), the only pinniped endemic to NZ, is rare and highly localised, with almost all breeding occurring in the outlying sub-Antarctic islands between 50-53 ̊S. The Auckland Islands comprise the largest breeding site, with three colony locations including Enderby, Dundas and Figure of Eight Islands, with a further two significant breeding locations on the more remote Campbell Island (Fig 1). At Sandy Bay, pregnant females give birth to a single pup with the median pupping date of approximately 26 December and the population is highly synchronised, with 69% of pups being born within a two week period [1]. Pup production has declined since 1995, for the seasons covered here pup production has been stable, albeit at just over 50% of the apparent Auckland Islands population peak in 2000–01 [3]
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