Abstract
The Anthropocene is a time of increasing human impact on environments, which is driving unprecedented changes in the epidemiology of wildlife disease worldwide. Marine mammals are impacted by many changes in the marine environment both directly and indirectly including run-off from agricultural and urban development on land. Marine mammals can be considered as sentinels of marine ecosystem health, so research on their health is beneficial to their conservation as well as the management of their environment.
New Zealand sea lions (Phocarctos hookeri) are the most threatened Otariid species worldwide, with most of their population living on subantarctic islands driven to the far reaches of their habitable range by historical hunting. They have experienced several epizootic events that had a significant impact on their population, which is in slow decline in subantarctic locations. The return of sea lions to Rakiura/Stewart Island and mainland New Zealand and strong population growth in these locations is therefore a positive development for the species, though their new synanthropic lifestyle brings its own risks.
Health research on New Zealand sea lions (NZSL) has focused on the causative agent of the subantarctic epizootic events, the bacterium Klebsiella pneumoniae and the hookworm (Uncinaria sp.) parasite associated with increased disease severity. Further research has also surveyed for zoonotic pathogens such as Toxoplasma gondii, Leptospira spp., and Brucella spp. However, little is known of the general parasite prevalence, abundance, and shedding patterns of parasites in NZSL.
This project aimed to begin to fill the knowledge gap on the parasites present in an apparently healthy population of sea lions by identifying the parasites present, their prevalence, differences in shedding numbers between seasons and demographic groups, and identifying those of zoonotic concern.
Faecal samples were collected from identifiable individual sea lions from March 2022 – February 2023 and examined using microscopic methods and molecular methods. Parasites from five different taxonomic groups were identified, including two genera known to cause clinical disease in infected humans. Seasonal, sex, age, and migratory factors were associated with different shedding patterns in different parasite groups, leading to further questions on the possibility of disease transmission between the different NZSL populations. In particular, protozoa and lungworm abundance differed between migratory and resident Otago sea lions, and there were significant seasonal differences in shedding of the zoonotic Anisakid nematode eggs.
The protozoan Neospora sp. was identified for the first time in NZSL using molecular methods and is of clinical importance where coinfection with Toxoplasma gondii occurs, with potential importance for regional livestock and dog health. Molecular analyses also confirmed the presence of eggs of the zoonotic nematode genus Anisakis in the faecal samples, and the bacterium Edwardsiella tarda which is an opportunistic pathogen of farmed fish and humans.
This project has provided a first insight into the parasite communities of NZSL in coastal Otago, which will improve our ability to detect future health changes in this population and inform future research on the subantarctic population. It has also contributed to the global pool of knowledge of parasites in otariid species. Further research opportunities highlighted by this thesis include a continuation of this non-invasive sampling method to increase sample sizes in coastal Otago and other NZSL populations, and more detailed examination of some of the parasite species present. This may include improved microscopic methods, biochemical assays, and more targeted molecular methods.