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Maui Island Modeling Scenarios for the Management of Axis Deer 1959-2014

August 23, 2021

Our objectives were to examine the population history of axis deer on Maui, estimate observed population growth, and then use species-specific demographic parameters in a VORTEX population viability analysis to examine removal scenarios that would most effectively reduce the population. Only nine deer were introduced in 1959, but recent estimates of less than 10,000 deer suggest population growth rates (r) ranging between 0.147 and 0.160 although at least 11,200 have been removed by hunters and resource managers. In the VORTEX simulations, we evaluated an initial population size of 6,000 females and 4,000 males, reflecting the probable 3F:2M sex ratio on Maui because of male biased hunting. Scenarios were modeled over a 10-year period with removal rates of 10%, 20%, and 30% of each annual population estimate, considering both growth and removals. A removal rate of 10% the annual population estimate (1,000 deer in the first year), and an evenly distributed effort that would remove an approximate ratio of 3F:2M resulted in a positive growth rate of 0.103 ± 0.001. A 20% removal rate resulted in only a slight negative growth, while a 30% removal rate dropped the estimate to 2,759 ± 15 deer in 10 years. By increasing the ratio of females removed to 4F:1M in the 30% removals scenario, the rate of decline nearly doubled and resulted in a mean population of 1,086 ± 15 deer. Our results indicate that effectively reducing an axis deer population would require an annual removal of approximately 20–30% of the estimated population and maintaining a ratio of 4F:1M would result in the steepest population decline.

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