Johnston David W.

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Johnston
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David W.
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  • Article
    Google haul out : Earth observation imagery and digital aerial surveys in coastal wildlife management and abundance estimation
    (Oxford University Press, 2017-06-14) Moxley, Jerry ; Bogomolni, Andrea L. ; Hammill, Mike O. ; Moore, Kathleen M. T. ; Polito, Michael J. ; Sette, Lisa ; Sharp, W. Brian ; Waring, Gordon T. ; Gilbert, James R. ; Halpin, Patrick N. ; Johnston, David W.
    As the sampling frequency and resolution of Earth observation imagery increase, there are growing opportunities for novel applications in population monitoring. New methods are required to apply established analytical approaches to data collected from new observation platforms (e.g., satellites and unmanned aerial vehicles). Here, we present a method that estimates regional seasonal abundances for an understudied and growing population of gray seals (Halichoerus grypus) in southeastern Massachusetts, using opportunistic observations in Google Earth imagery. Abundance estimates are derived from digital aerial survey counts by adapting established correction-based analyses with telemetry behavioral observation to quantify survey biases. The result is a first regional understanding of gray seal abundance in the northeast US through opportunistic Earth observation imagery and repurposed animal telemetry data. As species observation data from Earth observation imagery become more ubiquitous, such methods provide a robust, adaptable, and cost-effective solution to monitoring animal colonies and understanding species abundances.
  • Article
    Prevalence of influenza A virus in live-captured North Atlantic gray seals : a possible wild reservoir
    (Nature Publishing Group, 2016-08-03) Puryear, Wendy Blay ; Keogh, Mandy ; Hill, Nichola ; Moxley, Jerry ; Josephson, Elizabeth ; Davis, Kimberly Ryan ; Bandoro, Christopher ; Lidgard, Damian ; Bogomolni, Andrea L. ; Levin, Milton ; Lang, Shelley ; Hammill, Michael ; Bowen, Don ; Johnston, David W. ; Romano, Tracy ; Waring, Gordon T. ; Runstadler, Jonathan
    Influenza A virus (IAV) has been associated with multiple unusual mortality events (UMEs) in North Atlantic pinnipeds, frequently attributed to spillover of virus from wild-bird reservoirs. To determine if endemic infection persists outside of UMEs, we undertook a multiyear investigation of IAV in healthy, live-captured Northwest Atlantic gray seals (Halichoerus grypus). From 2013 to 2015, we sampled 345 pups and 57 adults from Cape Cod, MA, USA and Nova Scotia, Canada consistently detecting IAV infection across all groups. There was an overall viral prevalence of 9.0% (95% confidence interval (CI): 6.4%–12.5%) in weaned pups and 5.3% (CI: 1.2%–14.6%) in adults, with seroprevalences of 19.3% (CI: 15.0%–24.5%) and 50% (CI: 33.7%–66.4%), respectively. Positive sera showed a broad reactivity to diverse influenza subtypes. IAV status did not correlate with measures of animal health nor impact animal movement or foraging. This study demonstrated that Northwest Atlantic gray seals are both permissive to and tolerant of diverse IAV, possibly representing an endemically infected wild reservoir population.
  • Article
    Temporal and regional variability in the skin microbiome of humpback whales along the Western Antarctic Peninsula
    (American Society for Microbiology, 2017-12-21) Bierlich, Kevin C. ; Miller, Carolyn A. ; DeForce, Emelia A. ; Friedlaender, Ari S. ; Johnston, David W. ; Apprill, Amy
    The skin is the first line of defense between an animal and its environment, and disruptions in skin-associated microorganisms can be linked to an animal's health and nutritional state. To better understand the skin microbiome of large whales, high-throughput sequencing of partial small subunit ribosomal RNA genes was used to study the skin-associated bacteria of 89 seemingly healthy humpback whales (Megaptera novaeangliae) sampled along the Western Antarctic Peninsula (WAP) during early (2010) and late (2013) austral summers. Six core genera of bacteria were present in 93% or more of all humpback skin samples. A shift was observed in the average relative abundance of these core genera over time, with the emergence of four additional core genera corresponding to a decrease in water temperature, possibly caused by seasonal or foraging related changes in skin biochemistry that influenced microbial growth, or other temporal-related factors. The skin microbiome differed between whales sampled at several regional locations along the WAP, suggesting that environmental factors or population may also influence the whale skin microbiome. Overall, the skin microbiome of humpback whales appears to provide insight into animal and environmental-related factors and may serve as a useful indicator for animal health or ecosystem alterations.
  • Article
    Seasonal gain in body condition of foraging humpback whales along the Western Antarctic Peninsula
    (Frontiers Media, 2022-11-21) Bierlich, K. C. ; Hewitt, Joshua ; Schick, Robert S. ; Pallin, Logan ; Dale, Julian ; Friedlaender, Ari S. ; Christiansen, Fredrik ; Sprogis, Kate R. ; Dawn, Allison H. ; Bird, Clara N. ; Larsen, Gregory D. ; Nichols, Ross ; Shero, Michelle R. ; Goldbogen, Jeremy ; Read, Andrew J. ; Johnston, David W.
    Most baleen whales are capital breeders that use stored energy acquired on foraging grounds to finance the costs of migration and reproduction on breeding grounds. Body condition reflects past foraging success and can act as a proxy for individual fitness. Hence, monitoring the seasonal gain in body condition of baleen whales while on the foraging grounds can inform how marine mammals support the costs of migration, growth, and reproduction, as well as the nutritional health of the overall population. Here, we use photogrammetry from drone-based imagery to examine how the body condition of humpback whales (Megaptera novaeangliae) changed over the foraging season (November to June) along the Western Antarctic Peninsula (WAP) from 2017 to 2019. This population (IWC stock G) is recovering from past whaling and is growing rapidly, providing an opportunity to study how whales store energy in a prey-rich environment. We used a body area index (BAI) to estimate changes in body condition and applied a Bayesian approach to incorporate measurement uncertainty associated with different drone types used for data collection. We used biopsy samples to determine sex and pregnancy status, and a length-based maturity classification to assign reproductive classes (n= 228; calves = 31, juveniles = 82, lactating females = 31, mature males = 12, mature unknown sex = 56, non-pregnant females = 12, pregnant females = 3, pregnant & lactating females = 1). Average BAI increased linearly over the feeding season for each reproductive class. Lactating females had lower BAI compared to other mature whales late in the season, reflecting the high energetic costs of nursing a calf. Mature males and non-pregnant females had the highest BAI values. Calves and juvenile whales exhibited an increase in BAI but not structural size (body length) over the feeding season. The body length of lactating mothers was positively correlated with the body length of their calves, but no relationship was observed between the BAI of mothers and their calves. Our study establishes a baseline for seasonal changes in the body condition for this humpback whale population, which can help monitor future impacts of disturbance and climate change.
  • Article
    Shaped by their environment: variation in Blue Whale morphology across three productive coastal ecosystems
    (Oxford University Press, 2023-11-20) Barlow, Dawn R. ; Bierlich, Kevin C. ; Oestreich, William K. ; Chiang, Gustavo ; Durban, John W. ; Goldbogen, Jeremy A. ; Johnston, David W. ; Leslie, Matthew S. ; Moore, Michael J. ; Ryan, John P. ; Torres, Leigh G.
    Species ecology and life history patterns are often reflected in animal morphology. Blue whales are globally distributed, with distinct populations that feed in different productive coastal regions worldwide. Thus, they provide an opportunity to investigate how regional ecosystem characteristics may drive morphological differences within a species. Here, we compare physical and biological oceanography of three different blue whale foraging grounds: (1) Monterey Bay, California, USA; (2) the South Taranaki Bight (STB), Aotearoa New Zealand; and (3) the Corcovado Gulf, Chile. Additionally, we compare the morphology of blue whales from these regions using unoccupied aircraft imagery. Monterey Bay and the Corcovado Gulf are seasonally productive and support the migratory life history strategy of the Eastern North Pacific (ENP) and Chilean blue whale populations, respectively. In contrast, the New Zealand blue whale population remains in the less productive STB year-round. All three populations were indistinguishable in total body length. However, New Zealand blue whales were in significantly higher body condition despite lower regional productivity, potentially attributable to their non-migratory strategy that facilitates lower risk of spatiotemporal misalignment with more consistently available foraging opportunities. Alternatively, the migratory strategy of the ENP and Chilean populations may be successful when their presence on the foraging grounds temporally aligns with abundant prey availability. We document differences in skull and fluke morphology between populations, which may relate to different feeding behaviors adapted to region-specific prey and habitat characteristics. These morphological features may represent a trade-off between maneuverability for prey capture and efficient long-distance migration. As oceanographic patterns shift relative to long-term means under climate change, these blue whale populations may show different vulnerabilities due to differences in migratory phenology and feeding behavior between regions.