304 research outputs found
Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer
No full text© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sato, M., Trites, A. W., & Gauthier, S. Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer. Canadian Journal of Fisheries and Aquatic Sciences, 78(11), (2021): 1732–1743, https://doi.org/10.1139/cjfas-2020-0445.The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon, Oncorhynchus tshawytscha) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4–6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident killer whales are experiencing a prey shortage in the Salish Sea during summer and suggest a combination of other factors is affecting overall foraging success.This study was funded by Fisheries and Oceans Canada
Steller sea lion (<i>Eumetopias jubatus</i> (Schreber, 1776)) model fits.
No full text<p>Winship and Trites <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077389#pone.0077389-Winship1" target="_blank">[42]</a> (WT) (A1–A2) and Calkins and Pitcher <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077389#pone.0077389-Calkins1" target="_blank">[32]</a> (CP) (B1–B2).</p
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
Studying diving energetics of trained Steller sea lions in the open sea
No full textThe costs associated with diving are a central component of a sea lion's energy budget. Accurate estimates of diving costs are needed to assess energetic and physiological constraints on foraging behavior, including the potential effects of changes in prey distribution or density. However, information on sea lion diving physiology is limited to relatively few species of pinnipeds, and there is currently no information for Steller sea lions. Information on diving energetics of pinnipeds has traditionally been gathered using either wild or captive animals. Studies with wild animals are logistically challenging and are limited by the opportunistic nature of data collection, while studies in captivity have been constrained by the physical restrictions of the holding facility. To circumvent some of these limitations, we combined the best aspects of both techniques by conducting diving metabolism studies with trained Steller sea lions in an open ocean environment. Two captive-reared Steller sea lions were housed in a holding pen and transported by boat to a diving trial area. The animals were trained to dive to predetermined depths for controlled periods of time using an underwater light targeting system and a video system to monitor behavior. At the end of each dive the sea lions returned to a respirometry dome on the surface where oxygen consumption was measured to estimate diving metabolism. This paper describes the experimental setup used to evaluate diving metabolism, discusses the logistical challenges of the study and the advantages of using such an approach to carry out physiological experiments with sea lions, and provides preliminary data on the diving energetics of Steller sea lions.</p
Top predators, food webs, and ecosystem-based fisheries management (EBFM)
No full textNo abstracts are to be cited without prior reference to the author.Conveners:Chris Lynam (UK), Anita Gilles (Germany), Ian Mitchell (UK), Andrew W. Trites (PICES)
Due to the cancellation of ICES ASC 2020, some contributions submitted that year were also included in ASC 2021.</p
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
Bowhead whales use two foraging strategies in response to fine-scale differences in zooplankton vertical distribution
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fortune, S. M. E., Ferguson, S. H., Trites, A. W., Hudson, J. M., & Baumgartner, M. F. Bowhead whales use two foraging strategies in response to fine-scale differences in zooplankton vertical distribution. Scientific Reports, 10(1), (2020): 20249, doi:10.1038/s41598-020-76071-9.As zooplanktivorous predators, bowhead whales (Balaena mysticetus) must routinely locate patches of prey that are energy-rich enough to meet their metabolic needs. However, little is known about how the quality and quantity of prey might influence their feeding behaviours. We addressed this question using a new approach that included: (1) multi-scale biologging and unmanned aerial system observations of bowhead whales in Cumberland Sound, Nunavut (Canada), and (2) an optical plankton counter (OPC) and net collections to identify and enumerate copepod prey species through the water column. The OPC data revealed two prey layers comprised almost exclusively of lipid-rich calanoid copepods. The deep layer contained fewer, but larger, particles (10% greater overall biomass) than the shallow prey layer. Dive data indicated that the whales conducted long deep Square-shaped dives (80% of dives; averaging depth of 260.4 m) and short shallow Square-shaped dives (16%; averaging depth of 22.5 m) to feed. The whales tended to dive proportionally more to the greater biomass of zooplankton that occurred at depth. Combining behavioural recordings with prey sampling showed a more complex feeding ecology than previously understood, and provides a means to evaluate the energetic balance of individuals under current environmental conditions.Funding was awarded to S.H.F and provided by: Fisheries and Oceans Canada (Emerging Fisheries), World Wildlife Fund Canada (Arctic Species Conservation Fund), Nunavut Wildlife Research Trust Fund, Nunavut General Monitoring Program, Ocean Tracking Network and ArcticNet Centre of Excellence. Personal support was awarded to S.M.E.F and provided by Natural Sciences and Engineering Research Council Canadian Graduate Scholarship, Northern Scientific Training Program (Canadian Polar Commission), The Molson Foundation and the W.Garfield Weston Foundation
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