Improving Muskox Survey Methods

A group of muskox in the tundra outside of Nome.

This methods paper builds on much of the work we have been doing to further develop distance sampling methods over the last decade. Specifically, this paper extends the open-distance sampling approach we published in 2017 for sheep into an integrated population modeling framework. Doing so allows us to extract a full suite of demographic rates (e.g., survival, recruitment) for a given population while relying primarily on aerial survey data rather than a large marked population. More broadly, it provides a roadmap for how we can formally integrate targeted research efforts into long-term monitoring efforts, thereby leveraging the strengths of each. The efficiencies of these types of approaches can be substantial and we expect that many of our programs will benefit from their application going forward.

Using Distance Sampling‐Based Integrated Population Models to Identify Key Demographic Parameters

Abstract

Effective wildlife management relies on rigorous estimates of population parameters, although data for small populations are often sparse, limiting inference. Integrated population models (IPMs) offer a potential solution by formally combining data sets in a unified analysis, thereby improving precision and allowing the estimation of latent parameters. We expected that incorporating open‐population distance sampling models into an IPM framework would provide further advantages for assessing population dynamics, particularly for rare species. We present an open‐distance IPM combining separate sources of abundance, composition, survival, and harvest data to better understand the dynamics of a small (~200 individuals) muskox (Ovibos moschatus) population in northwestern Alaska, USA. There was a 75% chance the muskox population in our study area was declining (λ<1.0), primarily because of a −4.3%/year decline in adult females, and estimated survival probabilities were 0.70, 0.87, and 0.89 for yearlings, adult females, and adult males (harvest excluded), respectively. Insufficient numbers of recruits drove the decline in adult females, and harvest likely limited the adult male component of the population, accounting for up to 50% of mortalities. Together, these results suggest more conservative harvest management might be appropriate moving forward. In contrast, the results from a more conventional analysis were largely ambiguous, which would inevitably lead to delays in the application of appropriate management actions. Our work furthers the development of open‐population distance sampling models and IPMs and demonstrates an efficient approach for managing small populations when extensive marking of individuals is not possible.

Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Schmidt, J. H. and H. L. Robison. 2019. Using distance sampling-based integrated population models to identify key demographic parameters. The Journal of WIldlife Management DOI: 10.1002/jwmg.21805