Geology topics

Joel L. Garlich-Miller

Publications and source records attributed to Joel L. Garlich-Miller.

6 recordsLinked to original sources

USGS2024

Assessing the sustainability of Pacific walrus harvest in a changing environment

Harvest sustainability is a primary goal of wildlife management and conservation, and in a changing world, it is increasingly important to consider environmental drivers of population dynamics alongside harvest in cohesive management plans. This is particularly pertinent for harvested species that acutely experience effects of climate change. The Pacific walrus ( Odobenus rosmarus divergens ), a crucial subsistence resource for Indigenous communities, is simultaneously subject to rapid habitat loss associated with diminishing sea ice and an increasing anthropogenic footprint in the Arctic. We developed a theta-logistic population modeling-management framework to evaluate various harvest scenarios combined with 4 potential climate and disturbance scenarios (ranging from optimistic to pessimistic, based largely on sea ice projections from general circulation models) to simulate Pacific walrus population dynamics to the end of the twenty-first century, focusing on the independent-aged female subset of the population. We considered 2 types of harvest strategies: 1) state-dependent harvest scenarios wherein we calculated harvest as a percentage of the population and updated annual harvests at set intervals as the population was reassessed, and 2) annually consistent harvest scenarios wherein annual harvest levels remain consistent into the future. All climate and disturbance scenarios indicated declines of varying severity in Pacific walrus abundance to the end of the twenty-first century, even in the absence of harvest. However, we found that a state-dependent annual harvest of 1.23% of the independent-aged female subset of the population (e.g., 1,280 independent-aged females harvested in 2020, similar to contemporary harvest levels) met our criterion for sustainability under all climate and disturbance scenarios, considering a medium risk tolerance level of 25%. This indicates that the present rate of Pacific walrus harvest is sustainable and will continue to be—provided the population is assessed at regular intervals and harvest is adapted to match changes in population dynamics. Our simulations indicate that a sustainable annually-consistent harvest is also possible but only at low levels if the population declines as expected. Applying a constant annual harvest of 1,280 independent-aged females failed to meet our criterion for sustainability under 3 of the 4 climate and disturbance scenarios we evaluated and had a higher probability of quasi-extinction than an equivalent state-dependent harvest scenario (1.23%). We highlight the importance of state-dependent management strategies and suggest our modeling framework is useful for managing harvest sustainability in a changing climate.

Journal of Wildlife Management↗

USGS2024

Assessing the population consequences of disturbance and climate change for the Pacific walrus

Climate change and anthropogenic disturbance are increasingly affecting wildlife at a global scale. Predicting how varying types and degrees of disturbance may interact to influence population dynamics is a key management challenge. Population consequences of disturbance (PCoD) models provide a framework to link effects of anthropogenic disturbance on an individual’s behavior and physiology to population-level changes. In the present study, we develop a Pacific walrus ( Odobenus rosmarus divergens ) PCoD model to encompass the population-level effects of both anthropogenic disturbance and climate change. As the Arctic becomes increasingly ice-free, walruses spend more time at coastal (vs. ice-based) haulouts, from which they must expend more energy to reach foraging areas and where they have an elevated risk of mortality. Concurrently, sea ice loss is increasing the anthropogenic footprint in the Arctic (e.g. fisheries, shipping, energy exploration), which creates additional disturbance. We applied the PCoD model to 4 scenarios (ranging from optimistic to pessimistic) which incorporate different global sea ice model projections along with varying degrees of anthropogenic disturbance. All scenarios indicated a decline in Pacific walrus vital rates by the end of the 21st century, but our results demonstrated that the intensity of that decline could be mitigated by global efforts to reduce carbon emissions, along with local management and conservation efforts to protect important coastal haulouts and foraging grounds. In summary, we introduce a flexible PCoD modeling framework in a novel context which will prove useful to researchers studying species threatened by rapid environmental change.

Marine Ecology Progress Series↗

USGS2020

Panmixia in a sea ice-associated marine mammal: evaluating genetic structure of the Pacific walrus (Odobenus rosmarus divergens) at multiple spatial scales

The kin structure of a species at relatively fine spatial scales impacts broad-scale patterns in genetic structure at the population level. However, kin structure rarely has been elucidated for migratory marine mammals. The Pacific walrus ( Odobenus rosmarus divergens ) exhibits migratory behavior linked to seasonal patterns in sea ice dynamics. Consequently, information on the spatial genetic structure of the subspecies, including kin structure, could aid wildlife managers in designing future studies to evaluate the impacts of sea ice loss on the subspecies. We sampled 8,303 individual walruses over a 5-year period and used 114 single-nucleotide polymorphisms to examine both broad-scale patterns in genetic structure and fine-scale patterns in relatedness. We did not detect any evidence of genetic structure at broad spatial scales, with low F ST values (≤ 0.001) across all pairs of putative aggregations. To evaluate kin structure at fine spatial scales, we defined a walrus group as a cluster of resting individuals that were less than one walrus body length apart. We found weak evidence of kin structure at fine spatial scales, with 3.72% of groups exhibiting mean relatedness values greater than expected by chance, and a significantly higher overall observed mean value of relatedness within groups than expected by chance. Thus, the high spatiotemporal variation in the distribution of resources in the Pacific Arctic environment likely has favored a gregarious social system in Pacific walruses, with unrelated animals forming temporary associations.

Bering Sea↗

USGS2016

Pacific walrus coastal haulout database, 1852-2016— Background report

Walruses are large benthic predators that rest out of water between foraging bouts. Coastal “haulouts” (places where walruses rest) are formed by adult males in summer and sometimes by females and young when sea ice is absent, and are often used repeatedly across seasons and years. Understanding the geography and historical use of haulouts provides a context for conservation efforts. We summarize information on Pacific walrus haulouts from available reports (n =151), interviews with coastal residents and aviators, and personal observations of the authors. We provide this in the form of a georeferenced database that can be queried and displayed with standard geographic information system and database management software. The database contains 150 records of Pacific walrus haulouts, with a summary of basic characteristics on maximum haulout aggregation size, age-sex composition, season of use, and decade of most recent use. Citations to reports are provided in the appendix and as a bibliographic database. Haulouts were distributed across the coasts of the Pacific walrus range; however, the largest (maximum >10,000 walruses) of the haulouts reported in the recent 4 decades (n=19) were concentrated on the Russian shores in regions near the Bering Strait and northward into the western Chukchi Sea (n=17). Haulouts of adult female and young walruses primarily occurred in the Bering Strait region and areas northward, with others occurring in the central Bering Sea, Gulf of Anadyr, and Saint Lawrence Island regions. The Gulf of Anadyr was the only region to contain female and young walrus haulouts, which formed after the northward spring migration and prior to autumn ice formation.

Alaska↗

USGS2012

Potential population-level effects of increased haulout-related mortality of Pacific walrus calves

Availability of summer sea ice has been decreasing in the Chukchi Sea during recent decades, and increasing numbers of Pacific walruses have begun using coastal haulouts in late summer during years when sea ice retreats beyond the continental shelf. Calves and yearlings are particularly susceptible to being crushed during disturbance events that cause the herd to panic and stampede at these large haulouts, but the potential population-level effects of this mortality are unknown. We used recent harvest data, along with previous assumptions about demographic parameters for this population, to estimate female population size and structure in 2009 and project these numbers forward using a range of assumptions about future harvests and haulout-related mortality that might result from increased use of coastal haulouts during late summer. We found that if demographic parameters were held constant, the levels of harvest that occurred during 1990–2008 would have allowed the population to grow during that period. Our projections indicate, however, that an increase in haulout-related mortality affecting only calves has a greater effect on the population than an equivalent increase in harvest-related mortality distributed among all age classes. Therefore, disturbance-related mortality of calves at coastal haulouts may have relatively important population consequences.

Polar Biology↗

USGS2006

Development of airborne remote sensing methods for surveys of Pacific walrus

In April 2003, we conducted an operational test of an airborne multispectral scanner (AMS) over pack ice in the Bering Sea to evaluate the potential of this system as a survey tool for Pacific walruses. We scanned a total of 28,875 km2 of sea ice habitat at a spatial resolution of 4 m and collected high resolution photographs from a subset of the thermally detected walrus groups. We found a significant positive relationship between walrus group size and the amount of heat measured by the AMS and used this relationship to estimate total walrus numbers in the survey area. The number of walruses hauled out onto sea ice in our study area was estimated at 4,785 animals with a 95% confidence interval of 2,499–7,111. We believe that the AMS system as configured for this study would be a highly effective tool for surveying large areas of sea ice habitat for walrus groups. With a 6 km swath width, it should be possible to sample more 10,000 km2 in an 8-hr flight. Although walrus groups > 4 animals were easily detected and enumerated in the 4 m thermal data, the system was unable to detect individual walruses or seals ( Phoca spp . and Erignathus barbatus ). We found that most (94.6%) of the walruses photographed in our survey area occurred in groups > 6 animals, therefore we expect the magnitude of any bias due to undetected groups of hauled out animals would be relatively small.

Alaska↗