Akinori Takahashi

Akinori Takahashi
National Institute of Polar Research

About

167
Publications
43,250
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5,457
Citations
Citations since 2017
49 Research Items
3314 Citations
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20172018201920202021202220230100200300400500600
20172018201920202021202220230100200300400500600
20172018201920202021202220230100200300400500600

Publications

Publications (167)
Article
Full-text available
Since the last Arctic Monitoring and Assessment Programme (AMAP) effort to review biological effects of mercury (Hg) on Arctic biota in 2011 and 2018, there has been a considerable number of new Arctic bird studies. This review article provides contemporary Hg exposure and potential health risk for 36 Arctic seabird and shorebird species, represent...
Article
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The darkness of the deep ocean limits the vision of diving predators, except when prey emit bioluminescence. It is hypothesized that deep-diving seals rely on highly developed whiskers to locate their prey. However, if and how seals use their whiskers while foraging in natural conditions remains unknown. We used animal-borne tags to show that free-...
Article
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One direct consequence of Arctic warming is the expansion of navigable portions of the Arctic Ocean. As a result, vessel traffic and the accompanying threats of spills, strikes and disturbance is intensifying throughout the Arctic. In the Bering Sea, these threats to the environment, wildlife and to the people who rely on marine resources for food...
Article
Ocean circulation plays a key role in structuring marine ecosystems in the Southern Ocean. However, the seasonal dynamics of ocean circulation are poorly understood in the ice‐covered continental shelves due to difficulties in conducting observations. We, therefore, investigated spatial and temporal variations in oceanographic conditions and their...
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Small mesopelagic fishes dominate the world's total fish biomass, yet their ecological importance as prey for large marine animals is poorly understood. To reveal the little-known ecosystem dynamics, we identified prey, measured feeding events, and quantified the daily energy balance of 48 deep-diving elephant seals throughout their oceanic migrati...
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Seasonal resource pulses can have enormous impacts on species interactions. In marine ecosystems, air-breathing predators often drive their prey to deeper waters. However, it is unclear how ephemeral resource pulses such as near-surface phytoplankton blooms alter the vertical trade-off between predation avoidance and resource availability in consum...
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Migratory marine species cross political borders and enter the high seas, where the lack of an effective global management framework for biodiversity leaves them vulnerable to threats. Here, we combine 10,108 tracks from 5775 individual birds at 87 sites with data on breeding population sizes to estimate the relative year-round importance of nation...
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Like landscapes of fear, animals are hypothesized to strategically use lightscapes based on intrinsic motivations. However, longitudinal evidence of state-dependent risk aversion has been difficult to obtain in wild animals. Using high-resolution biologgers, we continuously measured body condition, time partitioning, three-dimensional movement, and...
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https://arctox.cnrs.fr/en/home/ Mercury (Hg) is a natural trace element found in high concentrations in top predators, including Arctic seabirds. Most current knowledge about Hg concentrations in Arctic seabirds relates to exposure during the summer breeding period when researchers can easily access seabirds at colonies. However, the few studies f...
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Plastic pollution, and its associated impacts on marine fauna due to chemical contamination, is an area of growing global concern. We analyzed 145 preen gland oil samples from 32 seabird species belonging to 8 families with different foraging habits and life history strategies from around the world for plastic additives and legacy persistent organi...
Article
Recent dramatic reductions of winter sea ice in the northern Bering Sea have raised the possibility that a rapid ecological transformation is underway. It has been hypothesized that with sufficient sea ice loss the cold pool thermal barrier separating the northern and southern Bering Sea would be breached, potentially benefiting piscivorous seabird...
Article
Die-offs of seabirds in Alaska have occurred with increased frequency since 2015. In 2018, on St. Lawrence Island, seabirds were reported washing up dead on beaches starting in late May, peaking in June, and continuing until early August. The cause of death was documented to be starvation, leading to the conclusion that a severe food shortage was t...
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Assessing impacts of environmental change on Arctic-breeding seabirds requires a better understanding of their year-round movement and foraging ecology. Here we examined the post-breeding movements and diving behavior of thick-billed (Uria lomvia) and common murres (U. aalge) breeding on St. Lawrence Island, northern Bering Sea, by using geolocator...
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Population trends and breeding success variability of Adélie penguins, a bioindicator of Antarctic environments, have been attributed to changing sea-ice extents; however, causative mechanisms remain unclear. By electronically tagging 175 penguins in four seasons with contrasting sea-ice conditions, we show that ice-free environments enhance, not d...
Article
Arctic ecosystems are altered profoundly by climate changes. However, the responses of Arctic marine and terrestrial ecosystems as well as their biodiversity to global warming remain largely unknown. This article provides comprehensive insights into the results and major findings from the Arctic Challenge for Sustainability (ArCS) Project – an Arct...
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Southern Ocean ecosystems are under pressure from resource exploitation and climate change1,2. Mitigation requires the identification and protection of Areas of Ecological Significance (AESs), which have so far not been determined at the ocean-basin scale. Here, using assemblage-level tracking of marine predators, we identify AESs for this globally...
Article
Theoretical models on the movement of colonial animals predict that neighbouring colonies may segregate their foraging areas, and many seabird studies have reported the presence of such segregations. However, they often lacked the appropriate null model to test the effect of neighbouring colonies on foraging areas, especially in small colonies or i...
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The Retrospective Analysis of Antarctic Tracking Data (RAATD) is a Scientific Committee for Antarctic Research project led jointly by the Expert Groups on Birds and Marine Mammals and Antarctic Biodiversity Informatics, and endorsed by the Commission for the Conservation of Antarctic Marine Living Resources. RAATD consolidated tracking data for mul...
Article
The Retrospective Analysis of Antarctic Tracking Data (RAATD) is a Scientific Committee for Antarctic Research project led jointly by the Expert Groups on Birds and Marine Mammals and Antarctic Biodiversity Informatics, and endorsed by the Commission for the Conservation of Antarctic Marine Living Resources. RAATD consolidated tracking data for mul...
Article
Knowledge of the diet of marine mammals is fundamental to understanding their role in marine ecosystems and response to environmental change. Recently, animal-borne video cameras have revealed the diet of marine mammals that make short foraging trips. However, novel approaches that allocate video time to target prey capture events is required to ob...
Article
During the breeding season, penguins travel tens or sometimes hundreds of kilometres between their nesting colony on land and foraging areas at sea (e.g. Ancel et al. 1992, Bost et al. 1997, Ryan et al. 2004, Cottin et al. 2012). For these movements, they use two locomotion modes with different speeds and costs of transport, i.e. swimming and walki...
Article
Marine methylmercury concentrations vary geographically and with depth, exposing organisms to different mercury levels in different habitats. Red-legged kittiwakes (Rissa brevirostris), a specialist predator, forage on fish and invertebrates from the mesopelagic zone, a part of the ocean with elevated methylmercury concentrations. We used kittiwake...
Article
Spatiotemporal dynamics of ecosystems can challenge the pertinence of Marine Protected Area (MPA) planning. Seasonal environmental changes are extreme in polar regions, however MPA planning in East Antarctica relies mostly on species' summer distribution only. Thirteen Adélie penguins were tracked from Ile des Pétrels (Terre Adélie), and their seas...
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Animal behavior is the final and integrated output of brain activity. Thus, recording and analyzing behavior is critical to understand the underlying brain function. While recording animal behavior has become easier than ever with the development of compact and inexpensive devices, detailed behavioral data analysis requires sufficient prior knowled...
Article
There have been efforts around the globe to track individuals of many marine species and assess their movements and distribution, with the putative goal of supporting their conservation and management. Determining whether, and how, tracking data have been successfully applied to address real-world conservation issues is, however, difficult. Here, w...
Preprint
Animal behavior is the final and integrated output of the brain activity. Thus, recording and analyzing behavior is critical to understand the underlying brain function. While recording animal behavior has become easier than ever with the development of compact and inexpensive devices, detailed behavioral data analysis requires sufficient previous...
Article
Full-text available
Prey size is an important factor for predators as it affects prey quality (energy content) and hence total energy gain. However, it remains challenging to obtain information about prey size from free‐ranging marine predators. Here, we developed a method that estimates prey size using mandible acceleration in captive northern elephant seals and then...
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Situated at high positions on marine food webs, seabirds accumulate high concentrations of persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane and its metabolites (DDTs), and hexachlorocyclohexanes (HCHs). Our previous studies proposed the usefulness of seabirds preen gland oil as a nondes...
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1.Interspecific competition can drive niche partitioning along multidimensional axes, including allochrony. Competitor matching will arise where the phenology of sympatric species with similar ecological requirements respond to climate change at different rates such that allochrony is reduced. 2.Our study quantifies the degree of niche segregation...
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Aim To provide a method of analyzing penguin tracking data to identify priority at‐sea areas for seabird conservation (marine IBAs), based on pre‐existing approaches for flying seabirds but revised according to the specific ecology of Pygoscelis penguin species. Location Waters around the Antarctic Peninsula, South Shetland, and South Orkney archi...
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Analyzing how animals are distributed in space and time is important to understand the behavioural interactions that underlie population dynamics, especially for highly social species. Thick-billed murres (Uria lomvia) breed in some of the largest and densest colonies of any seabird. Although this bird is known to aggregate at sea, little is known...
Article
Knowing the spatial scales at which effective management can be implemented is fundamental for conservation planning. This is especially important for mobile species, which can be exposed to threats across large areas, but the space use requirements of different species can vary to an extent that might render some management approaches inefficient....
Article
Knowing the spatial scales at which effective management can be implemented is fundamental for conservation planning. This is especially important for mobile species, which can be exposed to threats across large areas, but the space use requirements of different species can vary to an extent that might render some management approaches inefficient....
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Full-text available
In the Southern Ocean, the at-sea distributions of most predators of Antarctic krill are poorly known, primarily because tracking studies have only been undertaken on a restricted set of species, and then only at a limited number of sites. For chinstrap penguins, one of the most abundant krill predators breeding across the Antarctic Peninsula, we s...
Article
The Southern Ocean is currently experiencing major environmental changes, including in sea‐ice cover. Such changes strongly influence ecosystem structure and functioning and affect the survival and reproduction of predators such as seabirds. These effects are likely mediated by reduced availability of food resources. As such, seabirds are reliable...
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Specialization can make animals vulnerable to rapid environmental changes. For longlived seabirds, foraging specialization may make individuals especially sensitive, as climatic changes are currently occurring over the course of one lifetime. The Bering Sea is a dynamic subarctic and arctic ecosystem where windblown sea ice mediates annual producti...
Article
Pair bonds are considered important for successful breeding in monogamous birds, but their maintenance may be challenging for migratory species, as mates can be separated for months during the non-breeding period. To investigate whether mates of monogamous migratory seabirds stay together or not throughout the non-breeding period and how and when a...
Article
The identification of Ecologically or Biologically Significant Areas (EBSAs) as candidate Marine Protected Areas is a critical step in protecting marine ecosystems and biodiversity from the impacts of human activity. However, delineating EBSAs in offshore pelagic waters can be difficult due to the high cost of collecting biological information in s...
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Jellyfish and other pelagic gelatinous organisms (“gelata”) are increasingly perceived as an important component of marine food webs but remain poorly understood. Their importance as prey in the oceans is extremely difficult to quantify due in part to methodological challenges in verifying predation on gelatinous structures. Miniaturized animal-bor...
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Little is known about the foraging behavior of top predators in the deep mesopelagic ocean. Elephant seals dive to the deep biota-poor oxygen minimum zone (OMZ) (>800 m depth) despite high diving costs in terms of energy and time, but how they successfully forage in the OMZ remains largely unknown. Assessment of their feeding rate is the key to und...
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Antarctica and the Southern Ocean are increasingly affected by fisheries, climate change and human presence. Antarctic seabirds are vulnerable to all these threats because they depend on terrestrial and marine environments to breed and forage. We assess the current distribution and total abundance of Adélie penguins in East Antarctica and find ther...
Article
Modeling metapopulation dynamics is potentially a useful and powerful tool for ecologists and conservation biologists. However, the key processes driving metapopulation dynamics are colonization and extinction events, which are notoriously difficult to study. A recent global assessment of Adelie Penguin (Pygoscelis adeliae) breeding populations rep...
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Warm oceanographic conditions of the continental shelf regions in the southeastern Bering Sea are associated with drastic increases in the abundance of juvenile walleye pollock Gadus chalcogrammus at shallow depths. We hypothesized that thick-billed murres Uria lomvia would benefit from these warm conditions by taking advantage of such an abundant...
Article
Seabirds breeding on the Antarctic continent must cope with extreme changes in sea ice cover and day length throughout the year. Adélie penguins are expected to adjust their migratory movements and diving activity to seasonal changes in foraging conditions, but their winter diving activities have not been examined previously. Here, we tracked 18 an...
Article
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It is a golden age for animal movement studies and so an opportune time to assess priorities for future work. We assembled 40 experts to identify key questions in this field, focussing on marine megafauna, which include a broad range of birds, mammals, reptiles, and fish. Research on these taxa has both underpinned many of the recent technical deve...
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1. Temperature strongly regulates the distribution and fitness of ectotherms, and many studies have measured the temperature-dependence of physiological performance in controlled laboratory settings. In contrast, little is known about how temperature influences ectotherm performance in the wild, so the ecological significance of physiological perfo...
Article
Full-text available
It is a golden age for animal movement studies and so an opportune time to assess priorities for future work. We assembled 40 experts to identify key questions in this field, focussing on marine megafauna, which include a broad range of birds, mammals, reptiles, and fish. Research on these taxa has both underpinned many of the recent technical deve...
Article
Concern of pelagic gelatinous organisms takingover perturbed marine ecosystems has led to a recentincrease in research into this group. However, the significanceof this group as prey remains challenging to assess,and hence, gelatinous consumers are often depicted incorrectlyas dead ends of pelagic food webs. In the SouthernOcean, where a shift in t...
Article
Foraging theory predicts that predators adjust their movements according to the spatial distribution of prey. Since prey is often patchily distributed, area-restricted search (ARS) behaviour, characterized by sinuous search paths of predators with increased turning frequency, should be effective in foraging. However, it remains unclear whether ARS...
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Subarctic environmental changes are expected to affect the foraging ecology of marine top predators, but the response to such changes may vary among species if they use food resources differently. We examined the characteristics of foraging behavior of two sympatric congeneric diving seabird: common (Uria aalge: hereafter COMUs) and thick-billed (U...
Article
Full-text available
Seasonal sea-ice cover has been decreasing in the southeastern Bering Sea shelf, which might affect ecosystem dynamics and availability of food resources to marine top predators breeding in the region. In this study, we investigated the foraging responses of two seabird species, surface-foraging red-legged kittiwakes Rissa brevirostris (hereafter,...
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Background In animals, recoil motion resulting from underwater propulsion can destabilise trajectory and decrease locomotory performance. The posture of diving seabirds fluctuates simultaneously with their appendage beat, especially in the vertical plane, because of the recoil force of the beat. Seabirds that fly and swim face trade-offs between ma...
Article
Aim: In general, within temperate latitudes, races of endotherms tend to show larger body size at higher latitudes, while smaller bodied ones tend to be found at lower latitudes, a pattern known as Bergmann's rule (or James's rule for intra-specific patterns). The adaptive basis of this geographical variation in body size is explained mostly by the...
Article
The relationship between atmospheric bioaerosols and ecosystems is currently of global importance. Antarctica has an extreme climate, meaning that ecosystem behavior in this region is relatively simple. Direct sampling of atmospheric bioaerosols was performed at an Adélie penguin (Pygoscelis adeliae) colony at Hukuro Cove, Langhovde, Antarctica on...
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Sub-arctic environmental changes are expected to affect the ecology of marine top predators. We examined the characteristics of foraging behavior of two sympatric congeneric diving seabirds, common (Uria aalge: hereafter COMU) and thick-billed (U. lomvia: hereafter TBMU) murres breeding on St. George Island located in the seasonal sea-ice region of...
Article
Full-text available
Seasonal sea-ice cover has been decreasing in the southeastern Bering Sea shelf, which might affect ecosystem dynamics and availability of food resources to marine top predators breeding in the region. In this study, we investigated the foraging responses of two seabird species, surface-foraging red-legged kittiwakes Rissa brevirostris (hereafter,...
Article
Full-text available
Seabirds are considered to be useful and practical indicators of the state of marine ecosystems because they integrate across changes in the lower trophic levels and the physical environment. Signals from this key group of species can indicate broad scale impacts or response to environmental change. Recent studies of penguin populations, the most c...
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Narrow foraging specialization may increase the vulnerability of marine predators to climate change. The red-legged kittiwake (Rissa brevirostris) is endemic to the Bering Sea and has experienced drastic population fluctuations in recent decades, presumably due to climate-driven changes in food resources. Red-legged kittiwakes are presumed to be a...
Article
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Identifying marine features that support high foraging performance of predators is useful to determine areas of ecological importance. This study aimed to identify marine features that are important for foraging of chinstrap penguins (Pygoscelis antarcticus), an abundant upper-trophic level predator in the Antarctic Peninsula region. We investigate...