Abstract:

Wild boar (Sus scrofa) are of serious concern in numerous conservation areas such as El Palmar National Park, Argentina, where their increasing abundance affected the iconic palm tree Butia yatay. We assessed the effectiveness of an innovative management control program on wild boar population dynamics and ground rooting area over 10 years. Park personnel recruited and supervised local recreational hunters who regularly conducted controlled still shooting from widely distributed watchtowers and used trained dogs mainly during the first 2 years post-intervention (YPI). We used the detailed records of harvest and hunting effort to estimate time- and stage-specific catch-per-unit-effort (CPUE) indices and stochastic population growth rates (μ). Catch was linearly related to hunting effort except at large effort levels. CPUE indices declined exponentially at 5–7 % month−1 over 0–1 YPI and thereafter stabilized with μ indistinguishable from 0. Relative to baseline levels, culling reduced annual pregnancy rates, the fraction of juveniles and older adults, and ground rooting area below target values (<1.3 %). Incipient population recovery followed one of two periods of marginal hunting effort. The program generated few undesirable collateral effects mainly related to dog-hunting. Mesopredator abundance (foxes) steadily increased following a large outbreak of canine distemper at baseline. The combined use of standardized CPUE indices, body-length data and simple population viability analysis models provided reliable metrics for wild boar trend analysis and management. Unlike a preceding plan, a highly structured multi-stakeholder program proved to be sustainable and brought wild boar abundance to a low-density, unstable equilibrium causing minimal damage.

Author affiliation: Gurtler, Ricardo Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Author affiliation: Martín Izquierdo, V.. Administración de Parques Nacionales; Argentina

Author affiliation: Gil, Guillermo Pablo. Administración de Parques Nacionales; Argentina

Author affiliation: Cavicchia, Marcelo. Administración de Parques Nacionales; Argentina

Author affiliation: Maranta, Aristóbulo. Administración de Parques Nacionales; Argentina

Abstract:

Exotic ungulates are among the top global invasive mammals and a threat to biodiversity. Axis deer (Axis axis) and wild boar (Sus scrofa) are of increasing concern in multiple regions. A management program reduced wild boar abundance and soil damage below target levels through controlled still shooting from watchtowers and dog-hunting performed by recreational hunters at El Palmar National Park, Argentina. Here we assess program impacts on axis deer over a 10-year period in which 2380 deer were dispatched, and document two largely unexpected outcomes: increasing axis deer abundance toward a plateau, and a strong inverse correlation between deer and wild boar numbers. Unlike the initial steep decline and subsequent stabilization of wild boar, deer abundance indexed by standardized catch-per-unit-effort increased at 37.6% per year over 0–5 years post-intervention (YPI) and stabilized from 7 YPI on when still-shooting effort averaged 948 hunting party-hours per quarter. Deer catch was non-linearly related to still-shooting effort. Timing of deer and boar catches did not differ significantly regardless of sex, season and YPI. Catch-per-unit-effort indices and nightly spotlight deer counts showed similarly increasing trends. The fraction of older adult deer declined over 0–4 YPI and remained stable thereafter. Sex ratios were consistently skewed toward males only among older adults. Failure to reduce deer abundance may be explained by several major processes: protracted exponential growth of the deer population after park invasion; deer regional expansion with increasing immigration; insufficient sex- and stage-biased hunting mortality, and competitor (and perhaps predator) release from wild boar.

Author affiliation: Gurtler, Ricardo Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Author affiliation: Rodríguez Planes, Lucía Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Author affiliation: Gil, Guillermo. Administración de Parques Nacionales; Argentina

Author affiliation: Izquierdo, V. Martín. Administración de Parques Nacionales; Argentina

Author affiliation: Cavicchia, Marcelo. Administración de Parques Nacionales; Argentina

Author affiliation: Maranta, Aristóbulo. Administración de Parques Nacionales; Argentina