Long-term survival and reproductive success of New Zealand sea lions (Phocarctos hookeri) treated with ivermectin as pups
S. A. Michael A E , B. L. Chilvers B C , W. D. Roe D and B. D. Gartrell A
+ Author Affiliations
- Author Affiliations
A Wildbase, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North 4442, New Zealand.
B Marine Species and Threats, Department of Conservation, PO Box 10-420, Wellington, New Zealand.
C Present address: Wildbase, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North 4442, New Zealand.
D Pathobiology Group, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North 4442, New Zealand.
E Corresponding author. Email: sarah.a.michael@gmail.com
Wildlife Research 42(8) 660-667 https://doi.org/10.1071/WR15120
Submitted: 9 June 2015 Accepted: 2 November 2015 Published: 18 December 2015
Abstract
Context: Hookworms (Uncinaria spp.) are a common parasite of neonatal fur seals and sea lions around the world and may contribute to decreased pup growth and survival. Removal of these parasitic burdens by administration of the anthelmintic ivermectin has been trialled in New Zealand (NZ) sea lion (Phocarctos hookeri) pups at Sandy Bay, Enderby Island, with initial benefits in growth and survival reported. Long-term effects, however, are not known.
Aims: To determine the impact of ivermectin treatment administered in the first month of life, on long-term survival and fecundity in a sample of NZ sea lion pups.
Methods: For a sample of treated and control pups born between 2002 and 2004, resighting data to 2012 was assessed with the Cox proportional hazards analysis to evaluate survival to maturity and fecundity.
Key results: Sample size was a limiting factor as juvenile survival was very low, but a trend of improved survival was observed in the ivermectin-treated group. Year of birth was significant due to the effects of a bacterial epizootic in the first year of the trial. Reproductive rate was not significantly different between groups.
Conclusions: The effect of disease and parasitism on the survival of NZ sea lions is apparent, contributing to early pup mortality, with potentially wider-ranging implications for juvenile survival and beyond.
Implications: Further research is warranted to investigate anthelmintic treatment of NZ sea lion pups as a safe and effective management tool to improve survival and recruitment in declining populations.
Additional keywords: hookworm, ivermectin, management, pinniped, survival, survival analysis, Uncinaria.
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