How Immunocontraception Can Contribute to Elephant Management in Small, Enclosed Reserves: Munyawana Population as a Case Study

Immunocontraception has been widely used as a management tool to reduce population growth in captive as well as wild populations of various fauna. We model the use of an individual-based rotational immunocontraception plan on a wild elephant, Loxodonta africana, population and quantify the social and reproductive advantages of this method of implementation using adaptive management. The use of immunocontraception on an individual, rotational basis stretches the inter-calving interval for each individual female elephant to a management-determined interval, preventing exposing females to unlimited long-term immunocontraception use (which may have as yet undocumented negative effects). Such rotational immunocontraception can effectively lower population growth rates, age the population, and alter the age structure. Furthermore, such structured intervention can simulate natural process such as predation or episodic catastrophic events (e.g., drought), which regulates calf recruitment within an abnormally structured population. A rotational immunocontraception plan is a feasible and useful elephant population management tool, especially in a small, enclosed conservation area. Such approaches should be considered for other long-lived, social species in enclosed areas where the long-term consequences of consistent contraception may be unknown

Data from: Demography and social dynamics of an African elephant population 35 years after reintroduction as juveniles

1. Given their vulnerability to local extinction, the reintroduction of megafauna species (often long-lived, ecologically-influential and highly-social) is an increasingly relevant conservation intervention. Studies that evaluate past megafauna reintroductions are both critical and rare. 2. Between 1981 and 1996, 12 cohorts of a total of 200 juvenile (10 years old) composed 30% of the population in 2016. The population remains relatively young and forecasts suggest high potential for sustained growth over the next decade. 4. The first calf was born to a reintroduced female in 1990 and since then mother-calf units have gradually developed into semi-independent multi-generation families (7-15 individuals in size in 2016). The size of observed cow-calf groups was highly variable (mean=21.4 individuals, range: 7-109), with repeat observation of individual collared females revealing fusion and fission among different family groups through time, as is typical of more natural elephant populations. 5. Synthesis and applications: The development of normal elephant demography and sociality from an irregular founder population may be an encouragement for the reintroduction of other megaherbivores. The potential for rapid population growth must however be carefully considered, especially when ecologically-influential species are introduced to closed systems. The observed age class distribution and the estimated potential for future growth over the next decade have implications for the park’s contraception strategy. Finally, our study provides key long-term insights for elephant translocations, which are becoming an increasingly common and necessary management intervention (due to overpopulation in some areas and local extinction in others).04-Jun-201

Munyawana Conservancy.

<p>The dashed line indicates the position of the boundary fence between Phinda and the new sections of Zuka, and Mziki Pumalanga before the fences were removed during August 2004.</p

Modelled elephant population growth rate, population doubling time and population size for the contraception period 2006–2026.

i<p>Parameters for the age of sexual maturity were 8 years, 9 years (baseline) and 10 years.</p>ii<p>Parameters for the contraception implementation age were 8 years (prevent the first calf and only allow the first calf at 19 years after allowing an 8 year calving interval) or 10 years (baseline – allows the first natural birth, if the cow conceive at the baseline of 9 years age at sexual maturity).</p>iii<p>The length of time that a female was released from contraception to ensure conception, with the parameters of 1 year, 2 years (baseline) and 3 years.</p>iv<p>Parameters for the contraception induced calving intervals were 6 years, 8 years (baseline) and 10 years.</p>v<p>The growth rate was calculated for the 20-year time span (2006–2026) from the slope of regression on the natural log of population size against year.</p>vi<p>The time it takes for the population to double the starting numbers.</p>vii<p>The Munyawana elephant population total at the beginning of 2006, was calculated as if no females were on contraception for the past 3 years and would have conceived, accordingly a calving interval of 3 years was maintained from the age of the youngest calf.</p><p>The parameters for the eight individual modelled scenarios and the current implemented immunocontraception plans within the Munyawana population are presented within the table above.</p

The projected Phinda elephant population divided into age classes represented as absolute numbers under different immunocontraception scenarios.

<p>The age classes are classified as 0–2 years: infant, 2–4 years: juvenile, 5–8 years: intermediate, 9–12 years: sub-adults, older than 13 years are classified as an adult. Adult bulls are presented by white bars (with only two age classes), while all the individuals in the breeding herds are represented by the black bars which include males <13 years. (a). The Phinda elephant population in 2006 before any effects of immunocontraception had taken affect. The projected Phinda elephant population in 2026, (b). without any application of immunocontraception. (c). with a 100% application of immunocontraception. (d). with a rotational application of immunocontraception, as the current Phinda implemented immunocontraception plan.</p

Projected population size for the Munyawana elephant population under different immunocontraception scenarios for a 20-year time period.

<p>Results are shown for the current Munyawana immunocontraception plan, no application of immunocontraception on the population, and two contraception scenarios (Scenarios 6 and 7) that resulted in the most extreme projections. Scenario 6 was the prevention of the first calf and allowing the female to calf at 19 years of age, with a baseline contraception-induced calving interval of 8 years thereafter. Scenario 7 examined a shortened calving interval of 6 years.</p