Microsatellite assessment of walrus (&lt;i&gt;Odobenus rosmarus rosmarus&lt;/i&gt;) stocks in Canada

Shafer, Aaron B. A.; Davis, Corey S.; Coltman, David W.; Stewart, Robert E.

doi:10.7557/3.2607

Cited by 16 publications

(28 citation statements)

References 38 publications

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“…The levels of genetic variation were similar to those observed in walruses (0.53-0.61, Shafer et al 2014) and other pinnipeds (HE = 0.59 to 0.81; Palo et al 2001, Hoelzel et al 2001, Davis et al 2002, Acevedo-Whitehouse et al 2003 elsewhere. They are also consistent with results in Andersen et al (2009), which included a subsample of the animals in this study (HE = ranging from 0.59-0.66) that had been examined with fewer markers.…”

Section: Genetic Variationsupporting

confidence: 80%

A genetic comparison of West Greenland and Baffin Island (Canada) walruses: Management implications

et al. 2014

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Until recently Atlantic walruses (Odobenus rosmarus rosmarus) have been subject to relatively intense exploitation in West Greenland. Animals in this stock have also been hunted in Nunavut/Canada. However, the demographic identity of these animals and their connection with walruses in neighbouring areas is poorly resolved, hampering the determination of sustainable harvest levels. It has been suggested that walruses in West Greenland are genetically linked with walruses at SE Baffin Island (Canada) where they are also hunted for subsistence purposes. To determine the relationship(s) between walruses in these areas we conducted a genetic analysis including recent samples from West Greenland, Southeast Baffin Island in western Davis Strait, Hudson Strait in Canada and Northwest Greenland in northern Baffin Bay. Seventeen microsatellite markers were applied to all samples. Walruses in West Greenland and at Southeast Baffin Island did not differ from each other and therefore may be regarded as belonging to the same stock. However, walruses in these two areas differed genetically from both Northwest Greenland and Hudson Strait walruses. These findings support (1) that there are subunits within the range of walruses in the Hudson Strait-Davis Strait-Baffin Bay region and (2) that walruses along E Baffin Island and W Greenland constitute a common population that receive some influx from Hudson Strait. Thus, sustainable catch levels in Southeast Baffin Island (Nunavut) and in West Greenland must be set in light of the finding that they belong to the same stock, which is exploited in these two areas. This requires Canadian-Greenlandic co-management of the W Greenland-SE Baffin Island walrus stock.

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Section: Genetic Variationsupporting

confidence: 80%

A genetic comparison of West Greenland and Baffin Island (Canada) walruses: Management implications

et al. 2014

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“…Recent work using microsatellites showed that walruses in central Canada are subdivided into two large subpopulations – known as the high and central Arctic – that might be attributed to vicariance during the last glacial maximum (Shafer et al . ). Further, dispersal seems to be predominantly from the north to the south (Shafer et al .…”

Section: Introductionmentioning

confidence: 97%

“…Further, dispersal seems to be predominantly from the north to the south (Shafer et al . ) and the species showed no clear genetic signature of a bottleneck (Andersen et al . ).…”

Section: Introductionmentioning

confidence: 99%

Demographic inferences using short‐read genomic data in an approximate Bayesian computation framework: in silico evaluation of power, biases and proof of concept in Atlantic walrus

et al. 2015

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Approximate Bayesian computation (ABC) is a powerful tool for model-based inference of demographic histories from large genetic data sets. For most organisms, its implementation has been hampered by the lack of sufficient genetic data. Genotyping-by-sequencing (GBS) provides cheap genome-scale data to fill this gap, but its potential has not fully been exploited. Here, we explored power, precision and biases of a coalescent-based ABC approach where GBS data were modelled with either a population mutation parameter (θ) or a fixed site (FS) approach, allowing single or several segregating sites per locus. With simulated data ranging from 500 to 50 000 loci, a variety of demographic models could be reliably inferred across a range of timescales and migration scenarios. Posterior estimates were informative with 1000 loci for migration and split time in simple population divergence models. In more complex models, posterior distributions were wide and almost reverted to the uninformative prior even with 50 000 loci. ABC parameter estimates, however, were generally more accurate than an alternative composite-likelihood method. Bottleneck scenarios proved particularly difficult, and only recent bottlenecks without recovery could be reliably detected and dated. Notably, minor-allele-frequency filters - usual practice for GBS data - negatively affected nearly all estimates. With this in mind, we used a combination of FS and θ approaches on empirical GBS data generated from the Atlantic walrus (Odobenus rosmarus rosmarus), collectively providing support for a population split before the last glacial maximum followed by asymmetrical migration and a high Arctic bottleneck. Overall, this study evaluates the potential and limitations of GBS data in an ABC-coalescence framework and proposes a best-practice approach.

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“…When walrus were seen, we revised the coordinates for the haulout site as required. Shafer et al 2014). Stock designations as used here (Stewart 2008) In 2005, aerial surveys were conducted using a Messerschmitt-Bolkow-Blohm (BO-105-CBS) helicopter based on the Canadian Coast Guard (CCG) icebreaker Henry Larsen.…”

Section: Methodsmentioning

confidence: 99%

“…1), two of which are shared with Greenland (Born et al 1995, NAMMCO 2006, Stewart 2008, Andersen et al 2009, Dietz et al 2014). The Hudson Bay-Davis Strait (HB-DS) stock, part of the central-Arctic population of walrus in Canada (Shafer et al 2014) ranges from West Greenland to eastern Baffin Island and into Hudson Strait, although it is thought the occupancy range in this region has diminished in modern history (COSEWIC 2006). Walrus in this stock are hunted in both Canada and Greenland (Born et al 1995, Priest andUsher 2004) but there is only limited information on the size of the population that supports these harvests.…”

Section: Introductionmentioning

confidence: 99%

Estimates of Minimum Population Size for Walrus near Southeast Baffin Island, Nunavut

et al. 2014

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To support management objectives in Canada and Greenland, joint research between the Department of Fisheries and Oceans and Greenland Institute of Natural Resources was begun in 2005. Direct counts were used to determine the Minimum Counted Population (MCP) in summer around SE Baffin Island. Aerial surveys examined the coast from roughly the Saddleback Island in northern Hudson Strait to Isabella Bay on eastern Baffin Island but concentrated on the area between Loks Land and Cape Dyer. The maximum count was obtained on 3–4 September 2007 during boat surveys. The MCP ranged from 716 (in 2006) to 1,056 (2007). Using the largest MCP adjusted with published maximum estimates of the proportion of walrus hauled out concurrently, we estimated 1,420 (95% CI: 1,219–1,622) walrus were present. In addition, four walrus had been fitted with satellite relayed data logger tags prior to the maximum counts in 2007. Using the simple proportion of ‘tags dry’ on 3 September to adjust counts on 3 and 4 September 2007 provided an estimate of 2,102 (CI = MCP-4,482). Using the proportion of time dry immediately preceding the survey to adjust the maximum count produced an estimate of 2,502 (CI = 1,660–3,345) walrus were present in Hoare Bay. We conclude approximately 2,100–2,500 walrus were present in Hoare Bay in late summer 2007. This number is a negatively biased estimator of the population of walrus around SE Baffin Island and in the Hudson Bay–Davis Strait stock as a whole. Broader survey coverage in a short period and more detailed information on the movement of walrus between Greenland and Canada and the summer dispersal of these animals within Canada are required to improve population estimates.

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Microsatellite assessment of walrus (<i>Odobenus rosmarus rosmarus</i>) stocks in Canada

Cited by 16 publications

References 38 publications

A genetic comparison of West Greenland and Baffin Island (Canada) walruses: Management implications

A genetic comparison of West Greenland and Baffin Island (Canada) walruses: Management implications

Demographic inferences using short‐read genomic data in an approximate Bayesian computation framework: in silico evaluation of power, biases and proof of concept in Atlantic walrus

Estimates of Minimum Population Size for Walrus near Southeast Baffin Island, Nunavut

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