Investigation and mitigation of reduced fecundity and pup survival due to infectious disease in the endangered Australian sea lion, Neophoca cinerea

Abstract

The Australian sea lion (Neophoca cinerea) is endangered and declining, with high pup mortality additional to low fecundity. This thesis investigates infectious disease contribution to population size modulation, and the optimisation of a disease mitigation strategy. The first two data chapters advance existing knowledge of substantial pup morbidity attributable to hookworm (Uncinaria sanguinis) infection. Chapter two reports similar effectiveness for the novel use of the topical ivermectin formulation to the injected treatment, in a pilot study (n=85) at Dangerous Reef, Spencer Gulf, South Australia. Chapter three reports outcomes from the subsequent two-season treatment trial (n=322) of this formulation at Seal Bay, Kangaroo Island, South Australia. It quantifies significant negative haematological consequences of infection in the context of neonatal ontogenesis, provides the first reporting of significant (p<0.05) short- and longer-term treatment-related growth benefits in this species, and demonstrates optimal outcomes by the prevention of patent disease elaboration. Chapter four reports 30.4% (n=23) seroprevalence and high antibody titres in adult females for Toxoplasma gondii, indicating a comparable disease risk to other pinniped populations. An absence of detectable pup seroconversion (n=184) a lack of detectable congenital transmission or early post-natal infection, favouring a hypothesis of predominantly foraging-associated parasite exposure. Chapter five reports causation for mortality across five pup cohorts (n=122) at Seal Bay, identifying an infectious disease contribution in ~38% of deaths and modelling a significant (p<0.001) reduction in all-cause mortality risk with early hookworm elimination. Combined, this thesis confirms the substantial contribution of infectious disease to the species low pup survival and defines an effective mitigation strategy that could aid the species’ conservation.