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Ecology, management and conservation in natural and modified habitats
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RESEARCH ARTICLE
Contents Vol 32(6)

Control of feral cats for nature conservation. IV. Population dynamics and morphological attributes of feral cats at Shark Bay, Western Australia

Jeff Short A B and Bruce Turner A
+ Author Affiliations
- Author Affiliations

A CSIRO Sustainable Ecosystems, Private Bag 5, Wembley, WA 6913, Australia.

B Present address: Wildlife Research and Management, PO Box 1360, Kalamunda, WA 6926, Australia. Email: jeff.short@optusnet.com.au

Wildlife Research 32(6) 489-501 https://doi.org/10.1071/WR04102
Submitted: 29 October 2004  Accepted: 19 July 2005   Published: 18 October 2005

Abstract

The dynamics of feral cats (Felis catus) were assessed at Shark Bay at two adjoining sites subject to differing intensities of predator control. The Heirisson Prong conservation reserve (12 km2) was fenced to exclude predators and was subject to intensive control actions, while a portion of the adjoining Carrarang pastoral lease (60 km2) was subject to a lesser level of control. Foxes (Vulpes vulpes) were largely absent at both sites owing to effective control. Densities of cats were highly variable over time, showing strong annual fluctuations over 14 years of records Three independent estimates of peak density were made, varying between 1.5 and 2.8 km–2. Rate of increase was assessed as 0.98 on the pastoral lease and 0.99 on the conservation reserve (to give an approximate doubling of the population every 8.5 months). A logistic model, with K = 1.5 km–2 and r of 0.98, gave a maximum sustained yield of 0.37 cats km–2 year–1 and a harvest rate of >0.6 cats km–2 year–1 for their elimination in 5 years or less (for K = 2.8 km–2, these values increase to 0.69 and >1.05 km–2 year–1 respectively). Harvest outcomes at both sites were consistent with these models. However, the effort required to maintain a given offtake rate increased 6-fold at low cat densities and offtake by trapping as a function of cat density took the form of a Type 3 functional response. The functional response for cat trapping (the offtake with constant effort per unit time) overlaid against the curve of cat productivity suggested a stable equilibrium point at low cat densities (0.07–0.13 cats km–2). Hence, trapping effort needed to be greatly intensified at low cat densities and/or augmented by other methods of control to eradicate cats from the closed system of the reserve. The strongly male-biased sex ratio of captures at the barrier fence suggested high levels of reinvasion from beyond the harvested area of the pastoral lease and this made effective control in this open system difficult.


Acknowledgments

Shark Bay Salt Joint Venture provided generous financial and logistic support for this project and community members from Useless Loop provided diverse assistance over many years. We are very grateful for their support. We thank Danielle Risbey for access to her data from cyanide trials and for her management of the database on cat captures in the period 1992–96. Work described in this paper was approved by the CSIRO Sustainable Ecosystems Animal Ethics Committee and its predecessor (#01/02–12, 98/99–17, and WAAP 27). Mike Calver, Roger Pech, Danielle Risbey and Patrick Smith reviewed an earlier draft of this manuscript.


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