Killer whale respiration rates

Measuring breathing rates is a means by which oxygen intake and metabolic rates can be estimated to determine food requirements and energy expenditure of killer whales (Orcinus orca) and other cetaceans. This relatively simple measure also allows the energetic consequences of environmental stressors to cetaceans to be understood but requires knowing respiration rates while they are engaged in different behaviours such as resting, travelling and foraging. We calculated respiration rates for different behavioural states of southern and northern resident killer whales using video from UAV drones and concurrent biologging data from animal-borne tags. Behavioural states of dive tracks were predicted using hierarchical hidden Markov models (HHMM) parameterized with time-depth data and with labeled tracks of drone-identified behavioural states (from drone footage that overlapped with the time-depth data). Dive tracks were sequences of dives and surface intervals lasting ≥ 10 minutes cumulative duration. We calculated respiration rates and estimated oxygen consumption rates for the predicted behavioural states of the tracks. We found that juvenile killer whales breathed at a higher rate when travelling (1.6 breaths min-1) compared to resting (1.2) and foraging (1.5)-and that adult males breathed at a higher rate when travelling (1.8) compared to both foraging (1.7) and resting (1.3). The juveniles in our study were estimated to consume 2.5-18.3 L O2 min-1 compared with 14.3-59.8 L O2 min-1 for adult males across all behaviours based on estimates of mass-specific tidal volume and oxygen extraction. Our findings confirm that killer whales take single breaths between dives and indicate that energy expenditure derived from respirations requires using sex, age, and behavioural-specific respiration rates. These findings can be applied to bioenergetics models on a behavioural-specific basis, and contribute towards obtaining better predictions of dive behaviours, energy expenditure and the food requirements of apex predators.

Ultrasound images of the ascending aorta of anesthetized northern fur seals and Steller sea lions confirm that the aortic bulb maintains continuous blood flow

The increased size and enhanced compliance of the aortic bulb-the enlargement of the ascending aorta-are believed to maintain blood flow in pinnipeds during extended periods of diastole induced by diving bradycardia. The aortic bulb has been described ex vivo in several species of pinnipeds, but in vivo measurements are needed to investigate the relationship between structure and function. We obtained ultrasound images using electrocardiogram-gated transesophageal echocardiography during anesthesia and after atropine administration to assess the relationship between aortic bulb anatomy and cardiac function (heart rate, stroke volume, cardiac output) in northern fur seals (Callorhinus ursinus) and Steller sea lions (Eumetopias jubatus). We observed that the aortic bulb in northern fur seals and Steller sea lions expands during systole and recoils over the entire diastolic period indicating that blood flow is maintained throughout the entire cardiac cycle as expected. The stroke volumes we measured in the fur seals and sea lions fit the values predicted based on body size in mammals and did not change with increased heart rates, suggesting that greater stroke volumes are not needed for aortic bulb function. Overall, our results suggest that peripheral vasoconstriction during diving is sufficient to modulate the volume of blood in the aortic bulb to ensure that flow lasts over the entire diastolic period. These results indicate that the shift of blood into the aortic bulb of pinnipeds is a fundamental mechanism caused by vasoconstriction while diving, highlighting the importance of this unique anatomical adaptation.

Aquaculture related humpback whale entanglements in coastal waters of British Columbia from 2008-2021

Over the past two decades, increasing numbers of humpback whales have been returning to feed in the inshore waters of British Columbia (BC) where marine aquaculture farms are situated. This has led to growing concerns that the presence of aquaculture farms may pose an entanglement threat to humpback whales. However, it is not known whether aquaculture facilities attract humpback whales, or whether there are factors that increase the likelihood of humpback whale, becoming entangled and dying. We examined eight reports of humpback whales interacting with Atlantic salmon farms in BC from 2008 to 2021 to evaluate the conditions that may have contributed to their entanglements. Of the eight entangled humpbacks, three individuals died and five were successfully disentangled and released. All were young animals (1 calf, 7 subadults). Multiple factors were associated with two or more of the reported incidents. These included facility design, environmental features, seasonality, humpback whale age, and feeding behaviour. We found that humpback whales were most commonly entrapped in the predator nets of the aquaculture facilities (6/8 incidents), and were less often entangled in anchor support lines (2/8). The presence of salmon smolts did not appear to be an attractant for humpback whales given that half of the reported entanglements (4/8) occurred at fallowed salmon farms. Almost all of the entanglements (7/8) occurred in late winter (prior to the seasonal return of humpbacks) and during late fall (after most humpbacks have migrated south). Overall, the number of humpback whales impacted by fish farms was small compared to the numbers that return to BC (> 7,000) and accounted for <6% of all types of reported entanglements in BC. Human intervention was required to release humpback whales at fish farms, which points to the need to have well-established protocols to minimize entanglements and maximize successful releases.

Foraging behaviour and ecology of transient killer whales within a deep submarine canyon system

Transient killer whales have been documented hunting marine mammals across a variety of habitats. However, relatively little has been reported about their predatory behaviours near deep submarine canyons and oceanic environments. We used a long-term database of sightings and encounters with these predators in and around the Monterey Submarine Canyon, California to describe foraging behaviour, diet, seasonal occurrence, and habitat use patterns. Transient killer whales belonging to the outer coast subpopulation were observed within the study area 261 times from 2006-2021. Occurrences, behaviours, and group sizes all varied seasonally, with more encounters occurring in the spring as grey whales migrated northward from their breeding and calving lagoons in Mexico (March-May). Groups of killer whales foraged exclusively in open water, with individuals within the groups following the contours of the submarine canyon as they searched for prey. Focal follows revealed that killer whales spent 51% of their time searching for prey (26% of their time along the shelf-break and upper slope of the canyon, and 25% in open water). The remainder of their time was spent pursuing prey (10%), feeding (23%), travelling (9%), socializing (6%), and resting (1%). Prey species during 87 observed predation events included California sea lions, grey whale calves, northern elephant seals, minke whales, common dolphins, Pacific white-sided dolphins, Dall's porpoise, harbour porpoise, harbour seals, and sea birds. The calculated kill rates (based on 270 hours of observing 50 predation events) were 0.26 California sea lions per killer whale over 24 hours, 0.11 grey whale calves, and 0.15 for all remaining prey species combined. These behavioural observations provide insights into predator-prey interactions among apex predators over submarine canyons and deep pelagic environments.

Chinook salmon depth distributions on the continental shelf are shaped by interactions between location, season, and individual condition

BACKGROUND

Ecological and physical conditions vary with depth in aquatic ecosystems, resulting in gradients of habitat suitability. Although variation in vertical distributions among individuals provides evidence of habitat selection, it has been challenging to disentangle how processes at multiple spatio-temporal scales shape behaviour.

METHODS

We collected thousands of observations of depth from > 300 acoustically tagged adult Chinook salmon Oncorhynchus tshawytscha, spanning multiple seasons and years. We used these data to parameterize a machine-learning model to disentangle the influence of spatial, temporal, and dynamic oceanographic variables while accounting for differences in individual condition and maturation stage.

RESULTS

The top performing machine learning model used bathymetric depth ratio (i.e., individual depth relative to seafloor depth) as a response. We found that bathymetry, season, maturation stage, and spatial location most strongly influenced Chinook salmon depth. Chinook salmon bathymetric depth ratios were deepest in shallow water, during winter, and for immature individuals. We also identified non-linear interactions among covariates, resulting in spatially-varying effects of zooplankton concentration, lunar cycle, temperature and oxygen concentration.

CONCLUSIONS

Our results suggest Chinook salmon vertical habitat use is a function of ecological interactions, not physiological constraints. Temporal and spatial variation in depth distributions could be used to guide management decisions intended to reduce fishery impacts on Chinook salmon. More generally, our findings demonstrate how complex interactions among bathymetry, seasonality, location, and life history stage regulate vertical habitat selection.

An integrated system to assess marine extinctions

More than 20 global marine extinctions and over 700 local extinctions have reportedly occurred during the past 500 years. However, available methods to determine how many of these species can be confidently declared true disappearances tend to be data-demanding, time-consuming, and not applicable to all taxonomic groups or scales of marine extinctions (global [G] and local [L]). We developed an integrated system to assess marine extinctions (ISAME) that can be applied to any taxonomic group at any geographic scale. We applied the ISAME method to 10 case studies to illustrate the possible ways in which the extinction status of marine species can be categorized as unverified, possibly extinct, or extinct. Of the 10 case studies we assessed, the ISAME method concludes that 6 should be categorized as unverified extinctions due to problems with species' identity and lack of reliable evidence supporting their disappearance (periwinkle-Littoraria flammea [G], houting-Coregonus oxyrinchus [G], long-spined urchin-Diadema antillarum [L], smalltooth sawfish-Pristis pectinata [L], and largetooth sawfish-P. pristis [L]). In contrast, ISAME classified the Guadalupe storm-petrel (Oceanodroma macrodactyla [G]) and the lost shark (Carcharhinus obsolerus [G]) as possibly extinct because the available evidence indicates that their extinction is plausible-while the largetooth sawfish [L] and Steller's sea cow (Hydrodamalis gigas [G]) were confirmed to be extinct. Determining whether a marine population or species is actually extinct or still extant is needed to guide conservation efforts and prevent further biodiversity losses.

Data on the diets of Salish Sea harbour seals from DNA metabarcoding

Marine trophic ecology data are in high demand as natural resource agencies increasingly adopt ecosystem-based management strategies that account for complex species interactions. Harbour seal (Phoca vitulina) diet data are of particular interest because the species is an abundant predator in the northeast Pacific Ocean and Salish Sea ecosystem that consumes Pacific salmon (Oncorhynchus spp.). A multi-agency effort was therefore undertaken to produce harbour seal diet data on an ecosystem scale using, 1) a standardized set of scat collection and analysis methods, and 2) a newly developed DNA metabarcoding diet analysis technique designed to identify prey species and quantify their relative proportions in seal diets. The DNA-based dataset described herein contains records from 4,625 harbour seal scats representing 52 haulout sites, 7 years, 12 calendar months, and a total of 11,641 prey identifications. Prey morphological hard parts analyses were conducted alongside, resulting in corresponding hard parts data for 92% of the scat DNA samples. A custom-built prey DNA sequence database containing 201 species (192 fishes, 9 cephalopods) is also provided.

Electrocardiographic Scaling Reveals Differences in Electrocardiogram Interval Durations Between Marine and Terrestrial Mammals

Although the ability of marine mammals to lower heart rates for extended periods when diving is well documented, it is unclear whether marine mammals have electrophysiological adaptations that extend beyond overall bradycardia. We analyzed electrocardiographic data from 50 species of terrestrial mammals and 19 species of marine mammals to determine whether the electrical activity of the heart differs between these two groups of mammals. We also tested whether physiological state (i.e., anesthetized or conscious) affects electrocardiogram (ECG) parameters. Analyses of ECG waveform morphology (heart rate, P-wave duration, and PQ, PR, QRS, and QT intervals) revealed allometric relationships between body mass and all ECG intervals (as well as heart rate) for both groups of mammals and specific differences in ECG parameters between marine mammals and their terrestrial counterparts. Model outputs indicated that marine mammals had 19% longer P-waves, 24% longer QRS intervals, and 21% shorter QT intervals. In other words, marine mammals had slower atrial and ventricular depolarization, and faster ventricular repolarization than terrestrial mammals. Heart rates and PR intervals were not significantly different between marine and terrestrial mammals, and physiological state did not significantly affect any ECG parameter. On average, ECG interval durations of marine and terrestrial mammals scaled with body mass to the power of 0.21 (range: 0.19–0.23) rather than the expected 0.25—while heart rate scaled with body mass to the power of –0.22 and was greater than the widely accepted –0.25 derived from fractal geometry. Our findings show clear differences between the hearts of terrestrial and marine mammals in terms of cardiac timing that extend beyond diving bradycardia. They also highlight the importance of considering special adaptations (such as breath-hold diving) when analyzing allometric relationships.

Behavioral context of echolocation and prey-handling sounds produced by killer whales (Orcinus orca) during pursuit and capture of Pacific salmon (Oncorhynchus spp.)

Availability of preferred salmonid prey and a sufficiently quiet acoustic environment in which to forage are critical to the survival of resident killer whales (Orcinus orca) in the northeastern Pacific. Although piscivorous killer whales rely on echolocation to locate and track prey, the relationship between echolocation, movement, and prey capture during foraging by wild individuals is poorly understood. We used acoustic biologging tags to relate echolocation behavior to prey pursuit and capture during successful feeding dives by fish-eating killer whales in coastal British Columbia, Canada. The significantly higher incidence and rate of echolocation prior to fish captures compared to afterward confirms its importance in prey detection and tracking. Extremely rapid click sequences (buzzes) were produced before or concurrent with captures of salmon at depths typically exceeding 50 m, and were likely used by killer whales for close-range prey targeting, as in other odontocetes. Distinctive crunching and tearing sounds indicative of prey-handling behavior occurred at relatively shallow depths following fish captures, matching concurrent observations that whales surfaced with fish prior to consumption and often shared prey. Buzzes and prey-handling sounds are potentially useful acoustic signals for estimating foraging efficiency and determining if resident killer whales are meeting their energetic requirements.

Foraging habitat of North Atlantic right whales has declined in the Gulf of St. Lawrence, Canada, and may be insufficient for successful reproduction

Climate-induced changes in calanoid copepod (Calanus spp.) availability in traditional feeding areas might explain why a large proportion of the North Atlantic right whale Eubalaena glacialis population has fed in the Gulf of St. Lawrence (Canada) in recent years. However, little is known about the distribution of copepods in the gulf, and whether their abundance is sufficient to energetically sustain right whales. We used a mechanistic modelling approach to predict areas within the gulf that have foraging potential for adult female right whales, based on the annual energetic needs of resting, pregnant and lactating females, and their theoretical prey density requirements. We identified suitable foraging areas for right whales by coupling a foraging bioenergetics model with a 12 yr data set (2006-2017) describing the abundance and 3-dimensional distribution of late-stage Calanus spp. in the gulf. Prey densities in the southern gulf (from Shediac Valley to the Magdalen Islands) supported all 3 reproductive states in most (≥6) years. However, foraging habitat became progressively sparse in the southern gulf over time, with noticeably less suitable habitat available after 2014. Few other potentially suitable foraging areas were identified elsewhere in the gulf. Overall, the availability of foraging habitat in the gulf varied considerably between years, and was higher for resting females than for pregnant and lactating females. Our findings are consistent with the recent low calving rates, and indicate that prey biomass in the Gulf of St. Lawrence may be insufficient in most years to support successful reproduction of North Atlantic right whales.

Prey composition impacts lipid and protein digestibility in northern fur seals (Callorhinus ursinus)

Pinnipeds have specific macronutrient (protein, lipid) requirements to satisfy physiological functions, yet little is known about how diet characteristics affect macronutrient digestibility. We measured relative and absolute lipid and protein digestibility in six female northern fur seals (Callorhinus ursinus (Linnaeus, 1758)) fed eight experimental diets composed variously of four prey species (Pacific herring, Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847; walleye pollock, Gadus chalcogrammus Pallas, 1814 (formerly Theragra chalcogramma (Pallas, 1814)); capelin, Mallotus villosus (Müller, 1776); magister armhook squid, Berryteuthis magister (Berry, 1913)). We quantified how digestibility was affected by proximate composition of the diet (% lipid or % protein), levels of food mass and macronutrient intake, and tested for any potential benefit of multi-species diets. Overall, digestibility of both protein and lipid were high across diets, although macronutrient retention of lipids (96.0%–98.4%) was significantly higher than protein (95.7%–96.7%) for all but the two highest protein diets. Increased levels of protein intake resulted in increased protein retention, but decreased lipid digestibility. There was no evidence that mixed-species diets provide greater macronutrient digestibility over single-species diets. The results suggest that high to moderate lipid diets are more beneficial to northern fur seals because they lead to increased levels of lipid retention without large decreases in protein digestibility. This raises concerns that dietary factors may be contributing to the population declines of northern fur seals in the Bering Sea.

Growth and development of North Pacific gray whales (Eschrichtius robustus)

Understanding variability in growth patterns of marine mammals provides insights into the health of individuals and status of populations. Body growth of gray whales (Eschrichtius robustus) has been described for particular life stages, but has not been quantified across all ages. We derived a comprehensive growth equation for gray whales by fitting a two-phased growth model to age-specific length data of eastern North Pacific gray whales that were captured, stranded, or harvested between 1926 and 1997. To predict mass-at-age, we used the allometric relationship between mass and length. We found that on average (± SD), calves were 4.6 ± 0.043 m and 972 ± 26 kg at birth, and reached 8.5 ± 0.095 m and 6,019 ± 196 kg by the end of their first year of life (n = 118). Thus, calves almost double (2×) in length and octuple (8×) in mass while nursing, and are effectively about two-thirds of their asymptotic adult length and one-third of their maximum mass when weaned. The large sample of aged individuals (n = 730) indicates that gray whales live up to ~48 years and have a life expectancy of < 30 years. Adult females attain a mean (± SD) asymptotic size of 13.1 ± 0.048 m and 20,758 ± 222 kg, while the smaller males average 12.6 ± 0.048 m and 19,938 ± 222 kg at ~40 years of age. Females are thereby ~4% longer and heavier than males. These age-specific estimates of body size can be used to estimate food requirements and assess nutritional status of individuals.

Evidence of molting and the function of "rock-nosing" behavior in bowhead whales in the eastern Canadian Arctic

Bowhead whales (Balaena mysticetus) have a nearly circumpolar distribution, and occasionally occupy warmer shallow coastal areas during summertime that may facilitate molting. However, relatively little is known about the occurrence of molting and associated behaviors in bowhead whales. We opportunistically observed whales in Cumberland Sound, Nunavut, Canada with skin irregularities consistent with molting during August 2014, and collected a skin sample from a biopsied whale that revealed loose epidermis and sloughing. During August 2016, we flew a small unmanned aerial system (sUAS) over whales to take video and still images to: 1) determine unique individuals; 2) estimate the proportion of the body of unique individuals that exhibited sloughing skin; 3) determine the presence or absence of superficial lines representative of rock-rubbing behavior; and 4) measure body lengths to infer age-class. The still images revealed that all individuals (n = 81 whales) were sloughing skin, and that nearly 40% of them had mottled skin over more than two-thirds of their bodies. The video images captured bowhead whales rubbing on large rocks in shallow, coastal areas—likely to facilitate molting. Molting and rock rubbing appears to be pervasive during late summer for whales in the eastern Canadian Arctic.

Activity-specific metabolic rates for diving, transiting, and resting at sea can be estimated from time-activity budgets in free-ranging marine mammals

Time and energy are the two most important currencies in animal bioenergetics. How much time animals spend engaged in different activities with specific energetic costs ultimately defines their likelihood of surviving and successfully reproducing. However, it is extremely difficult to determine the energetic costs of independent activities for free-ranging animals. In this study, we developed a new method to calculate activity-specific metabolic rates, and applied it to female fur seals. We attached biologgers (that recorded GPS locations, depth profiles, and triaxial acceleration) to 12 northern (Callorhinus ursinus) and 13 Antarctic fur seals (Arctocephalus gazella), and used a hierarchical decision tree algorithm to determine time allocation between diving, transiting, resting, and performing slow movements at the surface (grooming, etc.). We concomitantly measured the total energy expenditure using the doubly-labelled water method. We used a general least-square model to establish the relationship between time-activity budgets and the total energy spent by each individual during their foraging trip to predict activity-specific metabolic rates. Results show that both species allocated similar time to diving (~29%), transiting to and from their foraging grounds (~26-30%), and resting (~8-11%). However, Antarctic fur seals spent significantly more time grooming and moving slowly at the surface than northern fur seals (36% vs. 29%). Diving was the most expensive activity (~30 MJ/day if done non-stop for 24 hr), followed by transiting at the surface (~21 MJ/day). Interestingly, metabolic rates were similar between species while on land or while slowly moving at the surface (~13 MJ/day). Overall, the average field metabolic rate was ~20 MJ/day (for all activities combined). The method we developed to calculate activity-specific metabolic rates can be applied to terrestrial and marine species to determine the energetic costs of daily activities, as well as to predict the energetic consequences for animals forced to change their time allocations in response to environmental shifts.

Lesser devil rays Mobula cf. hypostoma from Venezuela are almost twice their previously reported maximum size and may be a new sub-species

Three rays opportunistically obtained near Margarita Island, Venezuela, were identified as lesser devil rays Mobula cf. hypostoma, but their disc widths were between 207 and 230 cm, which is almost double the reported maximum disc width of 120 cm for this species. These morphometric data suggest that lesser devil rays are either larger than previously recognized or that these specimens belong to an unknown sub-species of Mobula in the Caribbean Sea. Better data are needed to describe the distribution, phenotypic variation and population structure of this poorly known species.

Fine-scale foraging movements by fish-eating killer whales (Orcinus orca) relate to the vertical distributions and escape responses of salmonid prey (Oncorhynchus spp.)

BACKGROUND

We sought to quantitatively describe the fine-scale foraging behavior of northern resident killer whales (Orcinus orca), a population of fish-eating killer whales that feeds almost exclusively on Pacific salmon (Oncorhynchus spp.). To reconstruct the underwater movements of these specialist predators, we deployed 34 biologging Dtags on 32 individuals and collected high-resolution, three-dimensional accelerometry and acoustic data. We used the resulting dive paths to compare killer whale foraging behavior to the distributions of different salmonid prey species. Understanding the foraging movements of these threatened predators is important from a conservation standpoint, since prey availability has been identified as a limiting factor in their population dynamics and recovery.

RESULTS

Three-dimensional dive tracks indicated that foraging (N = 701) and non-foraging dives (N = 10,618) were kinematically distinct (Wilks' lambda: λ16 = 0.321, P < 0.001). While foraging, killer whales dove deeper, remained submerged longer, swam faster, increased their dive path tortuosity, and rolled their bodies to a greater extent than during other activities. Maximum foraging dive depths reflected the deeper vertical distribution of Chinook (compared to other salmonids) and the tendency of Pacific salmon to evade predators by diving steeply. Kinematic characteristics of prey pursuit by resident killer whales also revealed several other escape strategies employed by salmon attempting to avoid predation, including increased swimming speeds and evasive maneuvering.

CONCLUSIONS

High-resolution dive tracks reconstructed using data collected by multi-sensor accelerometer tags found that movements by resident killer whales relate significantly to the vertical distributions and escape responses of their primary prey, Pacific salmon.

Physiological constraints and energetic costs of diving behaviour in marine mammals: a review of studies using trained Steller sea lions diving in the open ocean

Marine mammals are characterized as having physiological specializations that maximize the use of oxygen stores to prolong time spent under water. However, it has been difficult to undertake the requisite controlled studies to determine the physiological limitations and trade-offs that marine mammals face while diving in the wild under varying environmental and nutritional conditions. For the past decade, Steller sea lions (Eumetopias jubatus) trained to swim and dive in the open ocean away from the physical confines of pools participated in studies that investigated the interactions between diving behaviour, energetic costs, physiological constraints, and prey availability. Many of these studies measured the cost of diving to understand how it varies with behaviour and environmental and physiological conditions. Collectively, these studies show that the type of diving (dive bouts or single dives), the level of underwater activity, the depth and duration of dives, and the nutritional status and physical condition of the animal affect the cost of diving and foraging. They show that dive depth, dive and surface duration, and the type of dive result in physiological adjustments (heart rate, gas exchange) that may be independent of energy expenditure. They also demonstrate that changes in prey abundance and nutritional status cause sea lions to alter the balance between time spent at the surface acquiring oxygen (and offloading CO₂ and other metabolic by-products) and time spent at depth acquiring prey. These new insights into the physiological basis of diving behaviour further our understanding of the potential scope for behavioural responses of marine mammals to environmental changes, the energetic significance of these adjustments, and the consequences of approaching physiological limits.

Flipper strokes can predict energy expenditure and locomotion costs in free-ranging northern and Antarctic fur seals

Flipper strokes have been proposed as proxies to estimate the energy expended by marine vertebrates while foraging at sea, but this has never been validated on free-ranging otariids (fur seals and sea lions). Our goal was to investigate how well flipper strokes correlate with energy expenditure in 33 foraging northern and Antarctic fur seals equipped with accelerometers, GPS, and time-depth recorders. We concomitantly measured field metabolic rates with the doubly-labelled water method and derived activity-specific energy expenditures using fine-scale time-activity budgets for each seal. Flipper strokes were detected while diving or surface transiting using dynamic acceleration. Despite some inter-species differences in flipper stroke dynamics or frequencies, both species of fur seals spent 3.79 ± 0.39 J/kg per stroke and had a cost of transport of ~1.6–1.9 J/kg/m while diving. Also, flipper stroke counts were good predictors of energy spent while diving (R² = 0.76) and to a lesser extent while transiting (R² = 0.63). However, flipper stroke count was a poor predictor overall of total energy spent during a full foraging trip (R² = 0.50). Amplitude of flipper strokes (i.e., acceleration amplitude × number of strokes) predicted total energy expenditure (R² = 0.63) better than flipper stroke counts, but was not as accurate as other acceleration-based proxies, i.e. Overall Dynamic Body Acceleration.

Dive, food, and exercise effects on blood microparticles in Steller sea lions (Eumetopias jubatus): exploring a biomarker for decompression sickness

Recent studies of stranded marine mammals indicate that exposure to underwater military sonar may induce pathophysiological responses consistent with decompression sickness (DCS). However, DCS has been difficult to diagnose in marine mammals. We investigated whether blood microparticles (MPs, measured as number/μl plasma), which increase in response to decompression stress in terrestrial mammals, are a suitable biomarker for DCS in marine mammals. We obtained blood samples from trained Steller sea lions (Eumetopias jubatus, 4 adult females) wearing time-depth recorders that dove to predetermined depths (either 5 or 50 meters). We hypothesized that MPs would be positively related to decompression stress (depth and duration underwater). We also tested the effect of feeding and exercise in isolation on MPs using the same blood sampling protocol. We found that feeding and exercise had no effect on blood MP levels, but that diving caused MPs to increase. However, blood MP levels did not correlate with diving depth, relative time underwater, and presumed decompression stress, possibly indicating acclimation following repeated exposure to depth.

Net energy gained by northern fur seals (Callorhinus ursinus) is impacted more by diet quality than by diet diversity

Understanding whether northern fur seals (Callorhinus ursinus (L., 1758)) are negatively affected by changes in prey quality or diversity could provide insights into their on-going population decline in the central Bering Sea. We investigated how six captive female fur seals assimilated energy from eight different diets consisting of four prey species (walleye pollock (Gadus chalcogrammus Pallas, 1814, formerly Theragra chalcogrammus (Pallas, 1814)), Pacific herring (Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847), capelin (Mallotus villosus (Müller, 1776)), and magister armhook squid (Berryteuthis magister (Berry, 1913))) fed alone or in combination. Net energy was quantified by measuring fecal energy loss, urinary energy loss, and heat increment of feeding. Digestible energy (95.9%–96.7%) was high (reflecting low fecal energy loss) and was negatively affected by ingested mass and dietary protein content. Urinary energy loss (9.3%–26.7%) increased significantly for high-protein diets. Heat increment of feeding (4.3%–12.4%) was significantly lower for high-lipid diets. Overall, net energy gain (57.9%–83.0%) was affected by lipid content and varied significantly across diets. Mixed-species diets did not provide any energetic benefit over single-species diets. Our study demonstrates that diet quality was more important in terms of energy gain than diet diversity. These findings suggest that fur seals consuming low-quality prey in the Bering Sea would be more challenged to obtain sufficient energy to satisfy energetic and metabolic demands, independent of high prey abundance.

Dive behaviour can predict metabolic expenditure in Steller sea lions

Quantification of costs associated with foraging contributes to understanding the energetic impact that changes in prey availability have on the energy balance of an animal and the fitness of populations. However, estimating the costs of foraging is difficult for breath-hold divers, such as Steller sea lions, that feed underwater. We developed models parameterized with data from free-diving captive Steller sea lions to estimate the costs incurred by wild animals while foraging. We measured diving metabolic rate of trained sea lions performing four types of dives to 10 and 40 m in the open ocean and estimated the separate costs of different dive components: surface time; bottom time; and transiting to and from depth. We found that the sea lions' diving metabolic rates were higher while transiting (20.5 ± 13.0 ml O2 min(-1) kg(-1)) than while swimming at depth (13.5 ± 4.1 ml O2 min(-1) kg(-1)), and both were higher than metabolism at the surface (9.2 ± 1.6 ml O2 min(-1) kg(-1)). These values were incorporated into an energetic model that accurately predicted oxygen consumption for dives only (within 9.5%) and dive cycles (within 7.7%), although it consistently overestimated costs by 5.9% for dives and 21.8% for dive cycles. Differences in the costs of individual components of dives also explained differences in the efficiency of different dive strategies. Single dives were energetically less costly than bout dives; however, sea lions were more efficient at replenishing oxygen stores after bout dives and could therefore spend a greater portion of their time foraging than when undertaking single dives. The metabolic rates we measured for the different behavioural components of diving can be applied to time-depth recordings from wild Steller sea lions to estimate the energy expended while foraging. In turn, this can be used to understand how changes in prey availability affect energy balance and the health of individuals in declining populations.

Validating the relationship between 3-dimensional body acceleration and oxygen consumption in trained Steller sea lions

We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption ([Formula: see text]) in freely diving Steller sea lions (Eumetopias jubatus) while resting at the surface and diving. The trained sea lions executed three dive types-single dives, bouts of multiple long dives with 4-6 dives per bout, or bouts of multiple short dives with 10-12 dives per bout-to depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from [Formula: see text]. We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type were analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged, or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7-11 %, and standard error of the estimated AMR was 5-32 %. Overall, the extensive range of dive behaviors and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

Assessment of Competition between Fisheries and Steller Sea Lions in Alaska Based on Estimated Prey Biomass, Fisheries Removals and Predator Foraging Behaviour

A leading hypothesis to explain the dramatic decline of Steller sea lions (Eumetopias jubatus) in western Alaska during the latter part of the 20th century is a change in prey availability due to commercial fisheries. We tested this hypothesis by exploring the relationships between sea lion population trends, fishery catches, and the prey biomass accessible to sea lions around 33 rookeries between 2000 and 2008. We focused on three commercially important species that have dominated the sea lion diet during the population decline: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility) using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estimate the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass. Of 304 comparisons, we found 3 statistically significant relationships, all suggesting that sea lion populations increased with increasing prey accessibility. Given that the majority of comparisons showed no significant effect, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s.

Accelerometers identify new behaviors and show little difference in the activity budgets of lactating northern fur seals (Callorhinus ursinus) between breeding islands and foraging habitats in the eastern Bering Sea

We tagged 82 lactating northern fur seals (Callorhinus ursinus) with tri-axial accelerometers and magnetometers on two eastern Bering Sea islands (Bogoslof and St. Paul) with contrasting population trajectories. Using depth data, accelerometer data and spectral analysis we classified time spent diving (30%), resting (~7%), shaking and grooming their pelage (9%), swimming in the prone position (~10%) and two types of previously undocumented rolling behavior (29%), with the remaining time (~15%) unspecified. The reason for the extensive rolling behavior is not known. We ground-truthed the accelerometry signals for shaking and grooming and rolling behaviors—and identified the acceleration signal for porpoising—by filming tagged northern fur seals in captivity. Speeds from GPS interpolated data indicated that animals traveled fastest while in the prone position, suggesting that this behavior is indicative of destination-based swimming. Very little difference was found in the percentages of time spent in the categorical behaviors with respect to breeding islands (Bogoslof or St. Paul Island), forager type (cathemeral or nocturnal), and the region where the animals foraged (primarily on-shelf <200m, or off-shelf > 200m). The lack of significant differences between islands, regions and forager type may indicate that behaviors summarized over a trip are somewhat hardwired even though foraging trip length and when and where animals dive are known to vary with island, forager type and region.

A nutrigenomic approach to detect nutritional stress from gene expression in blood samples drawn from Steller sea lions

Gene expression profiles are increasingly being used as biomarkers to detect the physiological responses of a number of species to disease, nutrition, and other stressors. However, little attention has been given to using gene expression to assess the stressors and physiological status of marine mammals. We sought to develop and validate a nutrigenomic approach to quantify nutritional stress in Steller sea lions (Eumetopias jubatus). We subjected 4 female Steller sea lions to 3 feeding regimes over 70-day trials (unrestricted food intake, acute nutritional stress, and chronic nutritional stress), and drew blood samples from each animal at the end of each feeding regime. We then extracted the RNA of white blood cells and measured the response of 8 genes known to react to diet restriction in terrestrial mammals. Overall, we found that the genomic response of Steller sea lions experiencing nutritional stress was consistent with how terrestrial mammals respond to dietary restrictions. Our nutritionally stressed sea lions down-regulated some cellular processes involved in immune response and oxidative stress, and up-regulated pro-inflammatory responses and metabolic processes. Nutrigenomics appears to be a promising means to monitor nutritional status and contribute to mitigation measures needed to assist in the recovery of Steller sea lions and other at-risk species of marine mammals.

Feeding kinematics and performance of basal otariid pinnipeds, Steller sea lions (Eumetopias jubatus), and northern fur seals (Callorhinus ursinus): implications for the evolution of mammalian feeding

Feeding performance studies can address questions relevant to feeding ecology and evolution. Our current understanding of feeding mechanisms for aquatic mammals is poor. Therefore, we characterized the feeding kinematics and performance of 5 Steller sea lions (Eumetopias jubatus) and 6 northern fur seals (Callorhinus ursinus). We tested the hypotheses that both species use suction as their primary feeding mode, and that rapid jaw opening was related to suction generation. Steller sea lions used suction as their primary feeding mode, but also used a biting feeding mode. In contrast, Northern fur seals only used a biting feeding mode. Kinematic profiles of Steller sea lions were all indicative of suction feeding (i.e., a small gape, small gape angle, large depression of the hyolingual apparatus and lip pursing). However, jaw opening as measured by Gape Angle Opening Velocity (GAOV) was relatively slow in Steller sea lions. In contrast to Steller sea lions, the GAOV of Northern fur seals was extremely fast, but their kinematic profiles indicated a biting feeding mode (i.e., northern fur seals exhibited a greater gape, a greater gape angle, and minimal depression of the hyolingual apparatus compared to Steller sea lions). Steller sea lions produced both subambient and suprambient pressures at 45 kPa, respectively. In contrast, northern fur seals produced no detectable pressure measurements. Steller sea lions have a broader feeding repertoire than northern fur seals, which likely enables them to feed on a greater variety of prey, in more diverse habitats. Based on the basal phylogenetic position of northern fur seals, craniodental morphological data of the Callorhinus lineage, and the performance data provided in this study, we suggest that a northern fur seals may be exhibiting their ancestral feeding mode.

Inflation and deflation pressure-volume loops in anesthetized pinnipeds confirms compliant chest and lungs

We examined structural properties of the marine mammal respiratory system, and tested Scholander's hypothesis that the chest is highly compliant by measuring the mechanical properties of the respiratory system in five species of pinniped under anesthesia (Pacific harbor seal, Phoca vitulina; northern elephant seal, Mirounga angustirostris; northern fur seal Callorhinus ursinus; California sea lion, Zalophus californianus; and Steller sea lion, Eumetopias jubatus). We found that the chest wall compliance (CCW) of all five species was greater than lung compliance (airways and alveoli, CL) as predicted by Scholander, which suggests that the chest provides little protection against alveolar collapse or lung squeeze. We also found that specific respiratory compliance was significantly greater in wild animals than in animals raised in an aquatic facility. While differences in ages between the two groups may affect this incidental finding, it is also possible that lung conditioning in free-living animals may increase pulmonary compliance and reduce the risk of lung squeeze during diving. Overall, our data indicate that compliance of excised pinniped lungs provide a good estimate of total respiratory compliance.

Drag, but not buoyancy, affects swim speed in captive Steller sea lions

Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus) that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m) under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC) tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (∼12–26% subcutaneous fat). Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag) showed that swim speed was best predicted by two variables, drag and dive phase (AIC = −139). Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy.

Sensitivity to hypercapnia and elimination of CO2 following diving in Steller sea lions (Eumetopias jubatus)

The diving ability of marine mammals is a function of how they use and store oxygen and the physiological control of ventilation, which is in turn dependent on the accumulation of CO2. To assess the influence of CO2 on physiological control of dive behaviour, we tested how increasing levels of inspired CO2 (hypercarbia) and decreasing inspired O2 (hypoxia) affected the diving metabolic rate, submergence times, and dive recovery times (time to replenish O2 stores and eliminate CO2) of freely diving Steller sea lions. We also measured changes in breathing frequency of diving and non-diving individuals. Our findings show that hypercarbia increased breathing frequency (as low as 2 % CO2), but did not affect metabolic rate, or the duration of dives or surface intervals (up to 3 % CO2). Changes in breathing rates indicated respiratory drive was altered by hypercarbia at rest, but blood CO2 levels remained below the threshold that would alter normal dive behaviour. It took the sea lions longer to remove accumulated CO2 than it did for them to replenish their O2 stores following dives (whether breathing ambient air, hypercarbia, or hypoxia). This difference between O2 and CO2 recovery times grew with increasing dive durations, increasing hypercarbia, and was greater for bout dives, suggesting there could be a build-up of CO2 load with repeated dives. Although we saw no evidence of CO2 limiting dive behaviour, the longer time required to remove CO2 may eventually exhibit control over the overall time they can spend in apnoea and overall foraging duration.

Short-term episodes of imposed fasting have a greater effect on young northern fur seals (Callorhinus ursinus) in summer than in winter

An unexpected shortage of food may affect wildlife in a different way depending on the time of year when it occurs. We imposed 48 h fasts on six female northern fur seals (Callorhinus ursinus; ages 6-24 months) to identify times of year when they might be particularly sensitive to interruptions in food supply. We monitored changes in their resting metabolic rates and their metabolic response to thermal challenges, and also examined potential bioenergetic causes for seasonal differences in body mass loss. The pre-fast metabolism of the fur seals while in ambient air or submerged in water at 4°C was higher during summer (June to Sepember) than winter (November to March), and submergence did not significantly increase metabolism, indicating a lack of additional thermoregulatory costs. There was no evidence of metabolic depression following the fasting periods, nor did metabolism increase during the post-fast thermal challenge, suggesting that mass loss did not negatively impact thermoregulatory capacity. However, the fur seals lost mass at greater rates while fasting during the summer months, when metabolism is normally high to facilitate faster growth rates (which would ordinarily have been supported by higher food intake levels). Our findings suggest that summer is a more critical time of year than winter for young northern fur seals to obtain adequate nutrition.

Steller sea lions (Eumetopias jubatus) have greater blood volumes, higher diving metabolic rates and a longer aerobic dive limit when nutritionally stressed

Marine mammal foraging behaviour inherently depends on diving ability. Declining populations of Steller sea lions may be facing nutritional stress that could affect their diving ability through changes in body composition or metabolism. Our objective was to determine whether nutritional stress (restricted food intake resulting in a 10% decrease in body mass) altered the calculated aerobic dive limit (cADL) of four captive sea lions diving in the open ocean, and how this related to changes in observed dive behaviour. We measured diving metabolic rate (DMR), blood O2 stores, body composition and dive behaviour prior to and while under nutritional restriction. We found that nutritionally stressed sea lions increased the duration of their single long dives, and the proportion of time they spent at the surface during a cycle of four dives. Nutritionally stressed sea lions lost both lipid and lean mass, resulting in potentially lower muscle O2 stores. However, total body O2 stores increased due to rises in blood O2 stores associated with having higher blood volumes. Nutritionally stressed sea lions also had higher mass-specific metabolic rates. The greater rise in O2 stores relative to the increase in mass-specific DMR resulted in the sea lions having a longer cADL when nutritionally stressed. We conclude that there was no negative effect of nutritional stress on the diving ability of sea lions. However, nutritional stress did lower foraging efficiency and require more foraging time to meet energy requirements due to increases in diving metabolic rates and surface recovery times.

Improving accuracy of DNA diet estimates using food tissue control materials and an evaluation of proxies for digestion bias

Ecologists are increasingly interested in quantifying consumer diets based on food DNA in dietary samples and high-throughput sequencing of marker genes. It is tempting to assume that food DNA sequence proportions recovered from diet samples are representative of consumer's diet proportions, despite the fact that captive feeding studies do not support that assumption. Here, we examine the idea of sequencing control materials of known composition along with dietary samples in order to correct for technical biases introduced during amplicon sequencing and biological biases such as variable gene copy number. Using the Ion Torrent PGM(©) , we sequenced prey DNA amplified from scats of captive harbour seals (Phoca vitulina) fed a constant diet including three fish species in known proportions. Alongside, we sequenced a prey tissue mix matching the seals' diet to generate tissue correction factors (TCFs). TCFs improved the diet estimates (based on sequence proportions) for all species and reduced the average estimate error from 28 ± 15% (uncorrected) to 14 ± 9% (TCF-corrected). The experimental design also allowed us to infer the magnitude of prey-specific digestion biases and calculate digestion correction factors (DCFs). The DCFs were compared with possible proxies for differential digestion (e.g. fish protein%, fish lipid%) revealing a strong relationship between the DCFs and percent lipid of the fish prey, suggesting prey-specific corrections based on lipid content would produce accurate diet estimates in this study system. These findings demonstrate the value of parallel sequencing of food tissue mixtures in diet studies and offer new directions for future research in quantitative DNA diet analysis.

Inter-population movements of steller sea lions in Alaska with implications for population separation

Genetic studies and differing population trends support the separation of Steller sea lions (Eumetopias jubatus) into a western distinct population segment (WDPS) and an eastern DPS (EDPS) with the dividing line between populations at 144° W. Despite little exchange for thousands of years, the gap between the breeding ranges narrowed during the past 15–30 years with the formation of new rookeries near the DPS boundary. We analyzed >22,000 sightings of 4,172 sea lions branded as pups in each DPS from 2000–2010 to estimate probabilities of a sea lion born in one DPS being seen within the range of the other DPS (either ‘West’ or ‘East’). Males from both populations regularly traveled across the DPS boundary; probabilities were highest at ages 2–5 and for males born in Prince William Sound and southern Southeast Alaska. The probability of WDPS females being in the East at age 5 was 0.067 but 0 for EDPS females which rarely traveled to the West. Prince William Sound-born females had high probabilities of being in the East during breeding and non-breeding seasons. We present strong evidence that WDPS females have permanently emigrated to the East, reproducing at two ‘mixing zone’ rookeries. We documented breeding bulls that traveled >6,500 km round trip from their natal rookery in southern Alaska to the northern Bering Sea and central Aleutian Islands and back within one year. WDPS animals began moving East in the 1990s, following steep population declines in the central Gulf of Alaska. Results of our study, and others documenting high survival and rapid population growth in northern Southeast Alaska suggest that conditions in this mixing zone region have been optimal for sea lions. It is unclear whether eastward movement across the DPS boundary is due to less-optimal conditions in the West or a reflection of favorable conditions in the East.

Quantifying sequence proportions in a DNA-based diet study using Ion Torrent amplicon sequencing: which counts count?

A goal of many environmental DNA barcoding studies is to infer quantitative information about relative abundances of different taxa based on sequence read proportions generated by high-throughput sequencing. However, potential biases associated with this approach are only beginning to be examined. We sequenced DNA amplified from faeces (scats) of captive harbour seals (Phoca vitulina) to investigate whether sequence counts could be used to quantify the seals' diet. Seals were fed fish in fixed proportions, a chordate-specific mitochondrial 16S marker was amplified from scat DNA and amplicons sequenced using an Ion Torrent PGM™. For a given set of bioinformatic parameters, there was generally low variability between scat samples in proportions of prey species sequences recovered. However, proportions varied substantially depending on sequencing direction, level of quality filtering (due to differences in sequence quality between species) and minimum read length considered. Short primer tags used to identify individual samples also influenced species proportions. In addition, there were complex interactions between factors; for example, the effect of quality filtering was influenced by the primer tag and sequencing direction. Resequencing of a subset of samples revealed some, but not all, biases were consistent between runs. Less stringent data filtering (based on quality scores or read length) generally produced more consistent proportional data, but overall proportions of sequences were very different than dietary mass proportions, indicating additional technical or biological biases are present. Our findings highlight that quantitative interpretations of sequence proportions generated via high-throughput sequencing will require careful experimental design and thoughtful data analysis.

Prey patch patterns predict habitat use by top marine predators with diverse foraging strategies

Spatial coherence between predators and prey has rarely been observed in pelagic marine ecosystems. We used measures of the environment, prey abundance, prey quality, and prey distribution to explain the observed distributions of three co-occurring predator species breeding on islands in the southeastern Bering Sea: black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia), and northern fur seals (Callorhinus ursinus). Predictions of statistical models were tested using movement patterns obtained from satellite-tracked individual animals. With the most commonly used measures to quantify prey distributions - areal biomass, density, and numerical abundance - we were unable to find a spatial relationship between predators and their prey. We instead found that habitat use by all three predators was predicted most strongly by prey patch characteristics such as depth and local density within spatial aggregations. Additional prey patch characteristics and physical habitat also contributed significantly to characterizing predator patterns. Our results indicate that the small-scale prey patch characteristics are critical to how predators perceive the quality of their food supply and the mechanisms they use to exploit it, regardless of time of day, sampling year, or source colony. The three focal predator species had different constraints and employed different foraging strategies – a shallow diver that makes trips of moderate distance (kittiwakes), a deep diver that makes trip of short distances (murres), and a deep diver that makes extensive trips (fur seals). However, all three were similarly linked by patchiness of prey rather than by the distribution of overall biomass. This supports the hypothesis that patchiness may be critical for understanding predator-prey relationships in pelagic marine systems more generally.

A review of the effects of different marking and tagging techniques on marine mammals

Wildlife research often requires marking and tagging animals to collect data on survival, reproduction, movement, behaviour and physiology. Identification of individual marine mammals can be carried out using tags, brands, paint, dye, photogrammetry, telemetry and other techniques. An analysis of peer-reviewed articles published from January 1980 to April 2011 addressing the effects of marking revealed a preponderance of studies focussed on short-term effects such as injuries and behavioural changes. Some marking techniques were reported to cause pain and to change swimming and haul-out behaviour, maternal attendance, and duration of foraging trips. However, marking has typically not been found to affect survival. No published research has addressed other possible long-term effects of marking related to injuries or pain responses. Studies of the more immediate effects of marking (mostly related to externally attached devices such as radio-transmitters) have shown a variety of different types and magnitudes of responses. It is important to note that studies failing to find treament differences are less likely to be published, meaning that the present and any other reviews based on published literature may be a biased sample of all research conducted on the topic. Publishing results that found no or low impacts (i.e. best practices) as well as those that found significant impacts on animals should both be encouraged. Future research under more controlled conditions is required to document acute effects of marking, including injury and pain, and to better understand longer-term effects on health, reproduction and survival. We recommend that studies using marked animals standardise their reports, with added detail on methodology, monitoring and sampling design, and address practices used to minimise the impact of marking on marine mammals.

Dive behaviour impacts the ability of heart rate to predict oxygen consumption in Steller sea lions (Eumetopias jubatus) foraging at depth

The predictive relationship between heart rate (f(H)) and oxygen consumption (VO2) has been derived for several species of marine mammals swimming horizontally or diving in tanks to shallow depths. However, it is unclear how dive activity affects the f(H):VO2 relationship and whether the existing equations apply to animals diving to deeper depths. We investigated these questions by simultaneously measuring the f(H) and VO2 of Steller sea lions (Eumetopias jubatus) under different activity states (surface resting or diving), types of dives (single dives or dive bouts), and depths (10 or 40 m). We examined the relationship over dives only and also over dive cycles (dive + surface interval). We found that f(H) could only predict VO2 over a complete single dive cycle or dive bout cycle (i.e. surface intervals had to be included). The predictive equation derived for sea lions resting on the surface did not differ from that for single dive cycles. However, the equation derived over dive bout cycles (multiple dives + surface intervals) differed from those for single dive cycles or surface resting, with similar f(H) for multiple dive bout equations yielding higher predicted VO2 than that for single dive bout cycles (or resting). The f(H):VO2 relationships were not significantly affected by dive duration, dive depth, water temperature or cumulative food consumed under the conditions tested. Ultimately, our results demonstrate that f(H) can be used to predict activity-specific metabolic rates of diving Steller sea lions, but only over complete dive cycles that include a post-dive surface recovery period.

Convergent evolution in locomotory patterns of flying and swimming animals

Locomotion is one of the major energetic costs faced by animals and various strategies have evolved to reduce its cost. Birds use interspersed periods of flapping and gliding to reduce the mechanical requirements of level flight while undergoing cyclical changes in flight altitude, known as undulating flight. Here we equipped free-ranging marine vertebrates with accelerometers and demonstrate that gait patterns resembling undulating flight occur in four marine vertebrate species comprising sharks and pinnipeds. Both sharks and pinnipeds display intermittent gliding interspersed with powered locomotion. We suggest, that the convergent use of similar gait patterns by distinct groups of animals points to universal physical and physiological principles that operate beyond taxonomic limits and shape common solutions to increase energetic efficiency. Energetically expensive large-scale migrations performed by many vertebrates provide common selection pressure for efficient locomotion, with potential for the convergence of locomotory strategies by a wide variety of species.

Proportion of prey consumed can be determined from faecal DNA using real-time PCR

Reconstructing the diets of pinnipeds by visually identifying prey remains recovered in faecal samples is challenging because of differences in digestion and passage rates of hard parts. Analysing the soft-matrix of faecal material using DNA-based techniques is an alternative means to identify prey species consumed, but published techniques are largely nonquantitative, which limits their usefulness for some applications. We further developed and validated a real-time PCR technique using species-specific mitochondrial DNA primers to quantify the proportion of prey in the diets of Steller sea lions (Eumetopias jubatus), a pinniped species thought to be facing significant diet related challenges in the North Pacific. We first demonstrated that the proportions of prey tissue DNA in mixtures of DNA isolated from four prey species could be estimated within a margin of ∼ 12% of the percent in the mix. These prey species included herring Clupea palasii, eulachon Thaleichthyes pacificus, squid Loligo opalescens and rosethorn rockfish Sebastes helvomaculatus. We then applied real-time PCR to DNA extracted from faecal samples obtained from Steller sea lions in captivity that were fed 11 different combinations of herring, eulachon, squid and Pacific ocean perch rockfish (Sebastes alutus), ranging from 7% to 75% contributions per meal (by wet weight). The difference between the average percentage estimated by real-time PCR and the percentage of prey consumed was generally <12% for all diets fed. Our findings indicate that real-time PCR of faecal DNA can detect the approximate relative quantity of prey consumed for complex diets and prey species, including cephalopods and fish.