1,721,028 research outputs found
Energy requirements of grey whales
No full textEastern North Pacific grey whales (Eschrichtius robustus) rely on energy reserves obtained on their northern feeding grounds to complete their annual 17,000 km round-trip migration between the Arctic and Mexico. However, estimates of how much food is required to complete the annual migration is limited to adult whales of average size, and is not readily available across all age classes of males and females. I constructed an age-structured bioenergetics model using detailed information on the grey whale life cycle and migration timings to predict the energy requirements of different cohorts of grey whales. Results show that nursing calves require 24–35 L of milk daily in their first 9 to 10 months. Once weaned, juveniles require ~345 kg day⁻¹ of benthic invertebrates (4.5% of body weight), while the largest adult whales will need a minimum of ~870 kg day⁻¹ (4.3% of body weight) during the ~5 month (154 days) summer foraging season in the Arctic. In contrast, pregnant individuals need 1,630–1,969 kg of prey day⁻¹ (9.3–10.3% of body weight) during this same period to support foetal growth and store sufficient energy to produce milk once the calves are born in Mexico. Lactating whales returning to the Arctic with their calves will require 1,360–1,960 kg of prey day⁻¹ (8.2–8.9% of body weight) over the next 4.5 months to continue producing milk. My results can be combined with measured densities of benthic prey in the Arctic to assess and anticipate the likelihood of climate change or conspecific competition causing starvation-related mortality of grey whales in the future. My age-structured bioenergetics model is simple and flexible enough to adapt to any migratory species of interest, including rare, endangered species that may otherwise be considered data deficient.Science, Faculty ofResources, Environment and Sustainability (IRES), Institute forGraduat
Killer whale use of the inside waters of Vancouver Island, British Columbia
No full textKiller whales (Orcinus orca) play an important role in the coastal ecosystems of British
Columbia. In recent decades, west coast transient and southern resident killer whales (two of the
main ecotypes of killer whales in BC) have changed their use of coastal BC waters. However,
seasonal abundance and distribution changes, and reasons for why the changes occurred remain
relatively unknown. I used sighting reports of transient and southern resident killer whales from
2016-2023 in the inside waters of Vancouver Island (the Salish Sea and North Island Waters) to
evaluate how these ecotypes use the area, and the relative importance of the area to their
populations. I determined the proportion of the BC west coast transient killer whale population
that use the inside waters and compared these results with southern resident killer whale seasonal
variation in occupancy to analyze the difference in use of the Salish Sea between the two
ecotypes. I found that approximately 70% of the BC west coast transient population uses the
inside waters annually. Transient killer whales were present in the inside waters year-round, with
seasonal highs from March-September each year, which corresponded with the presence of prey
species that are drawn to the area during times that key fish species spawn. I also discovered an
odd vs. even year pattern in transient killer whale presence where transient abundance varies in
July of alternating years, which may be related to the return of pink salmon. Southern residents
were not observed consistently throughout the year in the Salish Sea and had a fluctuating
seasonal presence that peaked in March, July, September and November. These peaks also
corresponded with spawning times of key fish species that southern residents rely on for prey.
Overall, my results show that the inside waters of Vancouver Island are important for both
ecotypes of killer whales, and that their presence in the area relates to spawning seasons of key
fish species. These findings contribute to the conservation of west coast transient and southern
resident killer whales and highlights the need to maintain the health of the inside waters.Science, Faculty ofZoology, Department ofGraduat
Ecology, behaviour, and habitat use of transient killer whales in the California Current System
No full textTransient (mammal-eating) killer whales inhabiting the California Current Ecosystem—from southern British Columbia to southern California—belong to the genetically distinct west coast population. Variations in their association patterns and habitat use suggest that they are not a single uniform group. I analysed 2,232 georeferenced encounters with individually identified transient killer whales from 2005 to 2021 using data from dedicated surveys and opportunistic sightings. By applying behavioural, social, and geospatial analyses, I identified two subpopulations of west coast transients: an inner coast subpopulation that frequents nearshore coastal areas and an outer coast subpopulation that inhabits deeper waters near the continental shelf-break. The inner coast subpopulation consisted of 345 identified whales and is primarily found within 5 km of shore where they fed on pinnipeds and small cetaceans in nearshore waters. The outer coast subpopulation, with 211 identified whales, tended to occur within 9 km of the continental shelf break and in offshore areas near submarine canyons where they preyed on pelagic pinnipeds, oceanic dolphins, and large cetaceans. A detailed analysis of the predatory behaviours of outer coast transients showed that they exploited deep submarine canyons and oceanic environments. They also demonstrated seasonal variations in occurrences, behaviours, and group sizes—with more encounters occurring off California and in the spring as grey whales migrated northward from their breeding and calving lagoons in Mexico. Groups of killer whales foraged exclusively in open water, with individuals typically following the contours of submarine canyons as they searched for prey. The outer coast transients that were encountered near submarine canyons spent 50% of their time searching for prey, and the remainder pursuing prey, feeding, travelling, socializing, and resting. I analyzed sightings of 49 killer whales of unknown ecotype encountered in the deep oceanic waters offshore California and Oregon (>65 km), and concluded that they may represent a distinct oceanic subpopulation of transient killer whales or an undescribed mammal-eating oceanic population. These findings underscore the complex ecological, behavioural, and social structure of transient killer whales, and highlight the need for conservation strategies that address the distinct habitat preferences, prey choices, and social dynamics of these subpopulations.Science, Faculty ofOceans and Fisheries, Institute for theGraduat
Estimating the relative energetic cost of foraging in Pacific Coast Feeding Group grey whales from biologging data
No full textBiologging tags that record high-resolution tri-axial accelerometry data are proving to be integral
to the study of foraging ecology of large, free-roaming marine mammals, such as whales. They
have been applied to a number of baleen whale species that feed pelagically through lunges or
ram filtration to quantitatively define behaviours and estimate energetic costs. However, few
behavioural ecology studies using accelerometry data have been conducted on grey whales, a
unique baleen whale that performs benthic suction feeding. Using suction cup tri-axial
accelerometer tag deployments on 10 Pacific Coast Feeding Group (PCFG) grey whales along
the Oregon and Washington coasts, I defined signals of foraging behaviour at both the broad
state (dive) and foraging tactic (roll event) scales. I then estimated the relative energetic cost of
these behaviours using energy expenditure proxies derived from the accelerometry data—Overall
Dynamic Body Acceleration (ODBA; ms⁻²), stroke rate (Hz), stroke amplitude (radians per s),
and duration of dives with different foraging tactics performed (min). Hidden Markov Models
(HMMs) defined three biologically distinct states—forage, search, and transit—using turn angle,
dive duration, dive tortuosity and presence of roll events. Classification and Regression Tree
(CART) models best defined the foraging tactics of headstands, benthic digs, and side swims
using median pitch, depth to body length ratio, and absolute value of the median roll. These
definitions of grey whale foraging signals using accelerometry data add to the quantitative
descriptions of foraging behaviours previously described for baleen whales. Stroke rate identified
foraging and headstanding as being the most energetically costly activities at the broad state and
foraging tactic scales. These findings contribute to the foundational understanding of grey whale
foraging energetics needed to assess the impacts of various conservation concerns on the fitness
and interpret patterns of behaviour choice of this unique group of grey whales.Science, Faculty ofOceans and Fisheries, Institute for theGraduat
Mechanisms that facilitate and control the dive response in pinnipeds
No full textCardiovascular adaptations enable marine mammals to breath-hold dive for long durations. However, the mechanisms that maintain blood flow and control heart rate in diving mammals are not fully understood. To address this, I used ultrasound imaging, implantable cardiac monitors, and comparative methods in pinnipeds to determine 1) the adaptive function of the aortic bulb, 2) the implications of heart rate fluctuations during diving, and 3) the autonomic regulation of the circulatory system. Imaging the ascending aorta of anaesthetized Steller sea lions and northern fur seals supported the hypothesis that the aortic bulb maintains blood flow throughout the cardiac cycle and also indicated that stroke volume did not change with heart rate. These results suggest that the increased filling of the aortic bulb needed to support continual blood flow in the face of low diving heart rates is primarily driven by increased vascular resistance rather than increased stroke volume. Comparing my aortic bulb measurements of Steller sea lions and northern fur seals with five other pinniped species revealed that aortic bulb diameter scales allometrically and that species with relatively wider aortic bulbs dive for longer durations. These results indicate that the aortic bulb is a critical vascular adaptation to diving that supports the low heart rates that occur as part of the dive response. Heart rate monitoring in diving Steller sea lions demonstrated that heart rate slowly decreases and then oscillates throughout the dive. The rate at which heart rate initially declines appears to be related to the conditions of the dive, while the oscillations may reflect blood pressure regulation by the baroreflex. Measuring heart rate and heart rate variability in resting, free-moving, and diving Steller sea lions showed that diving resulted in the highest parasympathetic and baroreflex activity, affirming that heart rate is vagally controlled and blood pressure is actively managed during dives. Overall, these findings provide new insights into some of the cardiovascular adaptations that enhance the diving capabilities of marine mammals.Science, Faculty ofZoology, Department ofGraduat
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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