Restoration of a bighorn sheep population impeded by Mycoplasma ovipneumoniae exposure

Abstract

Bighorn sheep (Ovis canadensis) were once extirpated from the Black Hills region of South Dakota, U.S.A., mirroring declining populations throughout North America. Since the 1960s, several reintroductions have occurred in the Black Hills to reestablish populations, with varying success. We translocated 26 bighorn sheep from Alberta, Canada, to the Black Hills (February 2015) to restore bighorn sheep to their historic range. Due to prior examinations of cause‐specific survival, subsequent genetic diversity and disease prevalence analyses were required to evaluate success of the restoration effort. We measured a mean allelic diversity of 5.23 (SE = 0.44 [mean number of alleles]) and an observed heterozygosity of 0.71 (SE = 0.06; expected = 0.64 ± 0.05) in the translocated individuals. Translocated bighorn sheep tested negative for Mycoplasma ovipneumoniae at capture. An autogenous vaccine was administered prior to release in an attempt to safeguard the translocated bighorn sheep from infection with a strain known to be resident in adjacent bighorn sheep populations. However, the year following the translocation, a different strain of M. ovipneumoniae was associated with a pneumonia outbreak that resulted in 57.9% mortality. Our results suggest that allelic diversity and heterozygosity were sufficient for long‐term herd establishment, reducing the potential for founder effects. However, the overwhelming mortality associated with pneumonia, via the transfer of M. ovipneumoniae from an unknown source, limited the success or our reintroduction efforts. Successful attempts to restore bighorn sheep to their historic ranges must consider and mitigate potential routes for M. ovipneumoniae transmission pre‐ and post‐reintroduction.

A review of population and landscape level dynamics associated with pneumonia outbreaks in bighorn sheep with implications for land management

“…Future population level management can benefit from a clearer understanding of how population structure (e.g., population size, age classes) and contact with reservoir species can lead to pneumonia outbreaks and poor population recovery (Cassirer et al, 2018; Dassanayake et al, 2009; Lawrence et al, 2010; Manlove et al, 2014; Rovani et al, 2019). Landscape level research on genetic variation, metapopulation connectivity, and environmental heterogeneity can assist in developing broad scale management to reduce pneumonia outbreaks (Borg et al, 2017; Dekelaita et al, 2020; Gille et al, 2019; Poirier et al, 2019; Werdel et al, 2020). From this review, we identify key management questions that remain at both the population and landscape levels (Figure 3).…”

“…Managers frequently translocate bighorn sheep into new areas which can benefit adjacent populations or into unrelated populations, both of which can increase genetic diversity within the population, or to supplement population numbers. In many augmented populations, bighorn sheep exhibit greater reproductive success, larger‐bodied offspring, and either maintained or increased genetic diversity (Gille et al, 2019; Jahner et al, 2019; Love Stowell et al, 2020; Miller et al, 2012; Poirier et al, 2019; Werdel et al, 2020). However, translocating animals as a management tool to preserve genetic diversity across landscapes also requires additional considerations (Gille et al, 2019; Olson et al, 2013; Roffler et al, 2016; Thompson et al, 2001).…”

“…Higher individual fitness in some augmented bighorn sheep populations has been attributed to genetic rescue (e.g., Hogg et al, 2006), but many populations have still failed to recover (Singer et al, 2001;Singer, Papouchis, et al, 2000). Despite translocating animals to restore populations, additional factors including local adaptation and strain-specific immunity may hinder translocation success (Bleich et al, 2018;Werdel et al, 2020), and local pneumonia-associated extirpations remain a substantial threat to bighorn sheep. Pneumonia in bighorn sheep is a polymicrobial disease.…”

“…Translocated animals without local adaptations face added challenges when placed in novel environments. Other studies found translocated bighorn sheep had an increased risk of acquiring detrimental pathogens as compared to native populations, which had developed some level of immunity (Plowright et al, 2013;Werdel et al, 2020). Similarly, translocated animals can present a risk to native populations by introducing pneumonia pathogens from developed strain-specific immunities or lack of knowledge surrounding their infection status (i.e., not all individuals are typically tested).…”

Restoration of bighorn sheep: History, successes, and remaining conservation issues

“…If the presence of pathogens is confirmed, or if substantial uncertainty regarding health status of either the source or recipient (or nearby) populations exists, translocations should be avoided (Brewer et al, 2014). Even when such guidelines are followed, however, the potential for spillover or pathogen transmission between wild populations remains a reality (Werdel et al, 2020).…”