Habitat use, spatial ecology, and stable isotope variability of the Pacific harbor seal (Phoca vitulina richardii) along the Oregon coast

Pacific harbor seals (Phoca vitulina richardii) are one of Oregon’s most common coastal predators, numbering between 10,000 and 12,000 individuals (Brown et al. 2005b). They consume more than 149 species or types of marine prey within the Pacific Northwest, which include a large variety of commercially important fisheries species. Despite their potential economic impacts and ecological role, little quantitative data are available regarding individual harbor seal spatial foraging behaviors and dietary habits along the Oregon coast, particularly outside of their estuarine habitat. In order to examine the movement and dietary ecology of Pacific harbor seals in Oregon, I used satellite telemetry to track 24 adult harbor seals captured in two locations on the Oregon coast from September 2014 to September 2015. I also collected a whisker from each animal for dietary estimation via stable isotope analysis, namely the quantification of δ13C and δ15N enrichment as proxies for trophic level and spatial habitat use. These data were examined from three separate perspectives to highlight the ecological role of harbor seals along the Oregon coast. Chapter 1 is a quantitative assessment of spatial habitat utilization of Pacific harbor seals. I quantified individual and population-level home range area, core area, foraging trip distance and duration, percent presence within eleven inland waters including bays and rivers, proximity to two wave energy test sites, use of Oregon’s five marine reserves as well as marine protected areas and comparison areas, and percent use of inshore vs. at-sea habitats for all study animals. Chapter 2 is a multi-level examination of variability and assessment of behavioral repeatability for harbor seals. It included an examination of differences and predictability in spatial behavior and diet for seals at the levels of individual, capture site, and whole sample population. This was accomplished by measuring ‘repeatability’ of specific behaviors. Repeatability and spatial use were compared to stable isotopes in generalized linear and linear mixed effects models to highlight strategies in foraging. Chapter 3 investigates how local oceanography, dietary composition, and spatial movement were related for seals. I utilized generalized linear mixed models and linear mixed effects models to examine which environmental and site-related variables were most associated with movement and dietary patterns of the study animals. This was examined from a series of models of individually summarized parameters (n = 24), and from three models examining the point-by-point parameters of haulout status, in bay vs. at sea, and distance from shore (n = 57,220). Overall, this dissertation demonstrates associations between stable isotope-derived diet and patterns in spatial habitat use, suggesting that stable isotope analysis of δ13C and δ15N can inform two-dimensional satellite telemetry, but also may provide post-hoc information regarding drivers of spatial movement of harbor seals. Results revealed a high degree of between-individual variability in diet and spatial behavior, a limited use of Oregon’s newly established marine reserves and wave energy sites, and extensive utilization of Oregon’s continental shelf. This dissertation represents the first in-depth description of spatial habitat use for Pacific harbor seals, a common marine mammal and upper trophic-level predator, along the Oregon coast

Fecal Methylmercury Correlates With Gut Microbiota Taxa in Pacific Walruses (Odobenus rosmarus divergens)

ObjectivesMethylmercury metabolism was investigated in Pacific walruses (Odobenus rosmarus divergens) from St. Lawrence Island, Alaska, United States.MethodsTotal mercury and methylmercury concentrations were measured in fecal samples and paired colon samples (n = 16 walruses). Gut microbiota composition and diversity were determined using 16S rRNA gene sequencing. Associations between fecal and colon mercury and the 24 most prevalent gut microbiota taxa were investigated using linear models.ResultsIn fecal samples, the median values for total mercury, methylmercury, and %methylmercury (of total mercury) were 200 ng/g, 4.7 ng/g, and 2.5%, respectively, while in colon samples, the median values for the same parameters were 28 ng/g, 7.8 ng/g, and 26%, respectively. In fecal samples, methylmercury was negatively correlated with one Bacteroides genus, while members of the Oscillospirales order were positively correlated with both methylmercury and %methylmercury (of total mercury). In colon samples, %methylmercury (of total mercury) was negatively correlated with members of two genera, Romboutsia and Paeniclostridium.ConclusionsMedian %methylmercury (of total mercury) was 10 times higher in the colon compared to the fecal samples, suggesting that methylmercury was able to pass through the colon into systemic circulation. Fecal total mercury and/or methylmercury concentrations in walruses were comparable to some human studies despite differences in seafood consumption rates, suggesting that walruses excreted less mercury. There are no members (at this time) of the Oscillospirales order which are known to contain the genes to methylate mercury, suggesting the source of methylmercury in the gut was from diet and not in vivo methylation

Space use of Pacific harbor seals (Phoca vitulina richardii) from two haulout locations along the Oregon coast.

BackgroundThere are approximately 10,000-12,000 Pacific harbor seals (Phoca vitulina richardii) inhabiting the Oregon coast, and unlike other species of pinnipeds in this region, are reliably present year-round. Despite this, and drastic rebounds in population since the enactment of the Marine Mammal Protection Act, limited data is available for the present period regarding their space use at sea, and within estuarine, riverine, or bay areas within the state.ObjectiveTo examine site-based differences in space use for 24 adult Pacific harbor seals captured and outfitted with satellite transmitters at two predominant haulout sites on the Oregon Coast, USA.DesignWe captured 24 adult harbor seals from two haulout sites on the Central Oregon coast between September 2014-16 and fitted them with external Wildlife Computers SPOT5 satellite transmitters to track movement. Using state-space modeled locations derived from satellite telemetry data, we evaluated spatial behavior of these animals using a correlated random walk model via R package crawl. Kernel density estimation was subsequently used to calculate home range and core area for each animal. Percent use of open ocean habitat versus use of estuaries, rivers and bays was quantified, as was an initial examination of presence within five newly-established marine reserves in Oregon. Examination of haulout site-related differences in spatial behavior were examined for seals captured in Netarts and Alsea Bays, Oregon and haul out behavior related to time of day, season, and tidal level was also investigated.ResultsThe average individual home range for seals was 364.47 ± 382.87 km2 with seals captured in Alsea bay demonstrating a significantly higher home range area than those captured in Netarts Bay. Alsea bay seals also tended to range farther from shore than Netarts Bay animals. The average calculated core area for seals encompassed on average 29.41 ± 29.23 km2 per animal, however the home range of one animal was so small, core area could not be calculated. Use of marine reserves was limited for animals in this study, representing less than 2% of locations with a majority occurring in Cape Perpetua Marine Reserve and North Marine Protected Area. Seals were more likely to haul out during low tides and periods of low light (dusk, night and dawn), and hauling out behavior increased in winter months.SignificanceThese findings demonstrate the first major documentation of space use of harbor seals in the state for nearly three decades, and lends itself to future comparison and formation of mechanistically-based hypotheses for behavior of a common marine mammal in the highly productive northern California Current System

Harbour Seals: Population Structure, Status, and Threats in a Rapidly Changing Environment

The harbour seal (Phoca vitulina) is the world’s most widely distributed pinniped species ranging from temperate to Arctic regions (30–78.5° N in the Atlantic, 28–61.2° N in the Pacific), but no detailed overview of the species status exists. The aims of this review are to (i) provide current information on the genetic structure, population status, and threats; (ii) review potential consequences of a changing climate; and (iii) identify knowledge gaps to guide future research and monitoring. Although the species is globally abundant, wide differences exist across the species’ broad range. As climate warms, populations at the edges of the species’ distributional range are likely to be more affected. The primary climate-related drivers include: (i) changes in weather patterns, which can affect thermoregulation; (ii) decrease in availability of haul-out substrates; (iii) large-scale changes in prey availability and inter-specific competition; (iv) shifts in the range of pathogens; (v) increase in temperature favouring the biotransformation of contaminants; and (vi) increased exposure to pollutant from increased freshwater run-off. Multiple anthropogenic stressors may collectively impact some populations. Coordinated monitoring efforts across and within regions is needed. This would allow for a spatially explicit management approach including population-specific responses to known stressors

Best practice recommendations for the use of external telemetry devices on pinnipeds

Pinnipeds spend large portions of their lives at sea, submerged, or hauled-out on land, often on remote of-shore islands. This fundamentally limits access by researchers to critical parts of pinniped life history and has spurred the development and implementation of a variety of externally attached telemetry devices (ETDs) to collect informa‑ tion about movement patterns, physiology and ecology of marine animals when they cannot be directly observed. ETDs are less invasive and easier to apply than implanted internal devices, making them more widely used. However, ETDs have limited retention times and their use may result in negative short- and long-term consequences includ‑ ing capture myopathy, impacts to energetics, behavior, and entanglement risk. We identify 15 best practice recom‑ mendations for the use of ETDs with pinnipeds that address experimental justifcation, animal capture, tag design, tag attachment, efects assessments, preparation, and reporting. Continued improvement of best practices is critical within the framework of the Three Rs (Reduction, Refnement, Replacement); these best practice recommendations provide current guidance to mitigate known potential negative outcomes for individuals and local populations. These recommendations were developed specifcally for pinnipeds; however, they may also be applicable to studies of other marine taxa. We conclude with four desired future directions for the use of ETDs in technology development, valida‑ tion studies, experimental designs and data sharing