1,721,151 research outputs found
The fishery for Antarctic krill – conflicts between industrial production, protection of biodiversity, and legal governance
No full textThe Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for conserving the Antarctic marine ecosystem, where conservation also includes the management of commercial fisheries. The largest fishery (by weight) in Antarctic waters is that for Antarctic krill, a species vital to biogeochemical cycles and carbon sequestration, and a critical dietary item for a broad guild of marine predators. Fishing interests grew from the 1960s onwards, but catches then declined following the breakup of the Soviet Union. Now catches are again increasing, CCAMLR has been developing a revised krill fishery management framework intended to reduce ecosystem risks to predators at critical times of year. At the CCAMLR meeting in 2024, ongoing development of the revised framework was considered, however no progress was made. Progress is urgent, since part of the existing management approach was not renewed. Consequently, by default, catches in the southwest Atlantic may now aggregate in space and time; the interim catch limit for krill (620,000 t) can now be taken from anywhere and at any time, including at times and in places critical to krill predators, possibly with unintended consequences. Allowing catches to aggregate in space and time is something CCAMLR has long sought to avoid. Existing voluntary measures implemented by the fishery will help distribute catches, but are no substitute for de jure management. In addition to risks to the ecosystem, the current situation also presents risks for fishing nations and for CCAMLR itself. Rapid progress with the revised management framework now depends upon rebuilding consensus.</p
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Intra-seasonal variation in feeding rates and diel foraging behavior in a seasonally fasting mammal, the humpback whale (Megaptera novaeangliae)
Full text linkSouthern hemisphere humpbacks whales are seasonally fasting mammals who concentrate foraging in summer when Southern Ocean waters are most productive, coincident when their primary prey, the Antarctic krill, are most accessible. To accumulate blubber energy stores necessary to fuel energetically costly migrations and breeding events during the winter fasting period, humpbacks optimize foraging behaviors to exploit the ephemeral distribution and behavior of their prey. While humpback foraging in fall, prior to a northward migration, is well described, foraging upon arrival to the foraging grounds in summer is poorly understood. Between 2010-2019 we deployed suction cup attached biologgers onto 83 adult humpbacks along the Western Antarctic Peninsula throughout the austral summer and early fall. Tags remained attached for 18 hours on average, recording high resolution motion, depth and audio of the animal. Using idiosyncratic motion signals, we manually detected feeding lunges for each deployment, yielding 33,246 total detected lunge events between depths of 0 – 461 meters. Our results did not support previous hypotheses of increased humpback foraging from summer to fall along the WAP, conversely, we found a 51% reduction in daily feeding rates over the same period. There was nearly continuous daylight during the early summer period where whales fed during all hours of the day, this changed such that foraging occurred mostly during nighttime hours in the fall. Changes in lunge depths observed over the season indicate that humpbacks track the diel vertical migrations of krill that appear to change over the foraging season. Our results provide novel information on seasonal changes in foraging behavior of humpback whales and demonstrate that these animals, contrary to nearly all other animals that seasonally fast, likely maximize their food intake immediately upon exiting the fasting period. More direct information on krill densities concurrent to whale foraging would allow quantification of food intake to better test this hypothesis
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First Description of Migratory Behavior of Humpback Whales from an Antarctic Feeding Ground to a Tropical Breeding Ground
Full text linkDespite exhibiting one of the longest migrations in the world, half of the humpback whale migratory cycle has remained unexamined; until this point, no study has provided a continuous description of humpback whale migratory behavior from a feeding ground to a breeding ground. We present new information on the satellite derived offshore migratory movements of 16 humpback whales from Antarctic feeding grounds to South American breeding grounds. Satellite locations were used to demonstrate migratory corridors, while the impact of departure date on migration speed was assessed using a linear regression, and a Bayesian hierarchical state-space animal movement model was utilized to investigate the presence of feeding behavior en route. 35,642 Argos locations from 16 tagged whales from 2012-2017 were collected. The 16 whales were tracked for an average of 38.5 days of migration (range 10-151 days). The length of individually derived tracks ranged from 645–6,381 km. Southern hemisphere humpback whale populations are recovering quickly from intense commercial whaling and, around the Antarctic Peninsula, are doing so in the face of a rapidly changing environment. The current lack of scientific knowledge on marine mammal migration is a major barrier to cetacean conservation. This multi-year study sets a baseline against which the effects of climate change on humpback whales can be studied across years and conditions and provides an excellent starting point for the investigation into humpback whale migration
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Auditory Masking in Sea Lions, Seals, and Walruses
Full text linkDespite its importance within marine habitats, most of what we know about auditory masking is based on terrestrial species and theoretical assumptions about signal processing in animals. To fill data gaps and improve models that predict active listening space for marine mammals, I have measured hearing thresholds for tonal sounds with highly trained sea lions, walruses, and seals in the presence of precisely and experimentally varied background noise conditions. My aim is to provide empirical measurements of frequency-dependent masking parameters to inform a quantitative understanding of the acoustic scenarios encountered by free-ranging individuals. Three frequency-dependent aspects of masking are considered: critical ratios, critical bandwidths, and masker level effects. Critical ratios (CR), or the signal-to-noise ratios required for auditory detection of pure tones embedded in controlled, spectrally-flat noise, were measured for sea lion and walrus subjects across a frequency span from 0.2 to 16 kHz. Despite differences in hearing sensitivity, these masking metrics were similar for the subjects and followed expected frequency-dependent trends observed in terrestrial carnivores. When compared to published data for seals, sea lion and walrus CRs were generally higher, indicating that, among these marine Carnivores, seals are especially adapted for hearing in noise. To evaluate how the spectral content of noise contributes to masking, I determined the frequency bandwidth of noise that interferes with the detection of a given tonal signal, the ‘critical bandwidth’ (CBW). I conducted hearing measurements with three subjects–a sea lion, walrus, and seal–while varying the frequency content of surrounding noise. The study subjects showed an expected increase in absolute CBW with increasing frequency. While data for the sea lion and walrus were similar, the seal exhibited narrower CBWs that increased as a constant percentage of center frequency, further suggesting additional specialization for hearing in noise for this group. Finally, to explore how noise level contributes to masking, I conducted a series of tone detection measurements with one California sea lion in a highly controlled acoustic environment. Across experimental trials, I gradually increased the amplitude of surrounding noise from a level of no effect to capture masking onset. The data revealed a frequency-and bandwidth-dependent transition zone that occurs before complete masking is evident.
The reported masking parameters provide insight into how some marine mammals hear within noisy conditions. These data, obtained using behavioral, psychoacoustic methods, can be applied to estimate masking effects for amphibious marine carnivores listening in air or water. Further, because they extend to lower frequencies where noise tends to be high and few hearing data are available, these results have clear and actionable outcomes and implications for real-world scenarios and conservation. The findings identify the frequencies where these species are most vulnerable to noise, highlight differences in auditory biology among pinniped lineages, and enable improved predictions of the extent of masking in marine environments dominated by natural and anthropogenic noise
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Using Tissue Biomarkers to Understand the Demography and Recovery of Baleen Whales in a Rapidly Changing Environment
Full text linkBaleen whale populations in the Southern Ocean are recovering after intense commercial whaling in the 20th century. Along the Western Antarctic Peninsula (WAP), this recovery is occurring in one of the planet's most rapidly changing marine ecosystems. Understanding how climate-driven changes influence the population dynamics of whales in this region is critical for understanding what conservation and management actions must be prioritized to maintain the structure and function of this marine ecosystem. This is even more important as this region has seen extraordinary increases in industrial krill fishery pressure, which overlaps in both time and space with whales foraging in this region, as well as increased human presence in the form of ecotourism. Thus, to begin understanding the dynamics of whale recovery under continued environmental change, we need to study these whales' demography and population dynamics. My dissertation aimed to examine and describe the demographics and population dynamics of two species of Southern Hemisphere baleen whales (Antarctic minke whales and Southern Hemisphere humpback whales) in the context of a rapidly changing ecosystem. To do this, I used one of the most extensive, non-lethal tissue archives of these two species, collected as part of the National Science Foundations (NSF) Palmer Station long-term ecological research (LTER) project. I found that on average, Antarctic minke whales reproduced each year and estimated that two-thirds of females along the WAP were sexually mature. More importantly, these data represent the first non-lethal approach to studying this species. Furthermore, I found that broad-scale environmental variation affecting krill abundance and availability along the WAP adversely impacted humpback whale pregnancy rates. This indicates that continued warming along the WAP that results in subsequent changes in the distribution and abundance of prey may adversely affect the recovery of this humpback whale population. Lastly, I found that blubber cortisol levels were not significantly different between male and female humpback whales but were significantly different across different demographic groups of females and across months. Blubber cortisol levels also significantly decreased in 2021, a year when human presence along the WAP was greatly reduced due to the COVID-19 pandemic. These findings provide a critical baseline of cortisol levels for whales in a rapidly changing region and show direct relationships between cortisol levels and human presence.
These are some of the first non-lethal quantitative observations of the demography and population dynamics of recovering whale populations in the Antarctic and provide a critical reference point for future work as the Antarctic climate continues to change and populations continue to recover from whaling.
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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