Flipper Stroke Research Articles

Heart rate reduction during voluntary deep diving in free-ranging loggerhead sea turtles.

Air-breathing vertebrates exhibit cardiovascular responses to diving including heart rate reduction (diving bradycardia). Field studies on aquatic mammals and birds have shown that the intensity of bradycardia can vary depending on diving behaviour, such as the depth of dives and dive duration. However, in aquatic reptiles, the variation in heart rate during deep dives under natural conditions has not been fully investigated. In this study, we released five loggerhead sea turtles (Caretta caretta) outfitted with recorders into the sea and recorded their electrocardiogram, depth, water temperature and longitudinal acceleration. After 3days, the recorders automatically detached from the turtles. The heart rate signals were detected from the electrodes placed on the surface of the plastron. The mean (±s.d.) heart rate of 12.8±4.1beatsmin-1 during dives was significantly lower than that of 20.9±4.1beatsmin-1 during surface periods. Heart rate during dives varied with dive depth, although it remained lower than that at the surface. When the turtle dived deeper than 140m, despite the relatively high flipper stroke rate (approximately 19strokesmin-1), the heart rate dropped rapidly to approximately 2beatsmin-1 temporarily. The minimum instantaneous heart rate during dives was lower at deeper dive depths. Our results indicate that loggerhead sea turtles show variations in the intensity of diving bradycardia depending on their diving behaviour, similar to that shown by marine mammals and birds.

Home ranges and diving behavior of endangered New Zealand sea lions along the Catlins coast of South Island, New Zealand

AbstractNew Zealand sea lions (NZSL, Phocarctos hookeri) were extirpated from mainland New Zealand during pre‐European subsistence hunting. They began reoccupying South Island in 1994, and the newest breeding colony arose in 2006 along the Catlins Coast on southeastern South Island and currently consists of <10 individuals. The goal of this study was to use animal‐borne satellite telemeters and miniature data recorders (MDRs) to determine home ranges, three‐dimensional movements, and foraging strategy of female NZSL along the Catlins Coast during the austral winter of 2019. Total home ranges were small (97 km2) and primarily restricted to nearshore areas. Dives were shallow (8.9 m), short in duration (1.4 min), and had a mean swimming speed of 1.5 m s−1. We identified three dive types based primarily on total dive duration, mean maximum depth, total distance swam, and path linearity. The estimated at‐sea metabolic rate varied among dive types because of differences in flipper stroke frequency and swim speed. Female NZSL along the Catlins Coast have smaller home ranges and make shorter foraging trips compared with females in the Auckland Islands, and suitable habitat for breeding and prey availability along the southeast coast are encouraging for future population growth.

On the utility of accelerometers to predict stroke rate using captive fur seals and sea lions

ABSTRACTThe energy expenditure of free-living fur seals and sea lions is difficult to measure directly, but may be indirectly derived from flipper stroke rate. We filmed 10 captive otariids swimming with accelerometers either attached to a harness (Daily Diary: sampling frequency 32 Hz, N=4) or taped to the fur (G6a+: 25 Hz, N=6). We used down sampling to derive four recording rates from each accelerometer (Daily Diary: 32, 16, 8, 4 Hz; G6a+: 25, 20, 10, 5 Hz). For each of these sampling frequencies, we derived 20 combinations of two parameters (RMW, the window size used to calculate the running mean; and m, the minimum number of points smaller than a local maxima used to detect a peak) from the dynamic acceleration of x, z and x+z, to estimate stroke rate from the accelerometers. These estimates differed by up to ∼20% in comparison to the actual number of foreflipper strokes counted from videos. RMW and the choice of axis used to make the calculations (x, z or x+z) had little effect on the overall differences, though the variability was reduced when using x+z. The best m varied depending on the axis used and the sampling frequency; a larger m was needed for higher sampling frequencies. This study demonstrates that when parameters are appropriately tuned, accelerometers are a simple yet valid tool for estimating the stroke rates of swimming otariids.

Flipper stroke rate and venous oxygen levels in free-ranging California sea lions.

The depletion rate of the blood oxygen store, development of hypoxemia and dive capacity are dependent on the distribution and rate of blood oxygen delivery to tissues while diving. Although blood oxygen extraction by working muscle would increase the blood oxygen depletion rate in a swimming animal, there is little information on the relationship between muscle workload and blood oxygen depletion during dives. Therefore, we examined flipper stroke rate, a proxy of muscle workload, and posterior vena cava oxygen profiles in four adult female California sea lions (Zalophus californianus) during foraging trips at sea. Flipper stroke rate analysis revealed that sea lions minimized muscle metabolism with a stroke-glide strategy when diving, and exhibited prolonged glides during the descent of deeper dives (>100 m). During the descent phase of these deep dives, 55±21% of descent was spent gliding, with the longest glides lasting over 160 s and covering a vertical distance of 340 m. Animals also consistently glided to the surface from 15 to 25 m depth during these deeper dives. Venous hemoglobin saturation (SO2 ) profiles were highly variable throughout dives, with values occasionally increasing during shallow dives. The relationship between SO2 and flipper stroke rate was weak during deeper dives, while this relationship was stronger during shallow dives. We conclude that (1) the depletion of oxygen in the posterior vena cava in deep-diving sea lions is not dependent on stroke effort, and (2) stroke-glide patterns during dives contribute to a reduction of muscle metabolic rate.

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.

Averaged Propulsive Body Acceleration (APBA) Can Be Calculated from Biologging Tags That Incorporate Gyroscopes and Accelerometers to Estimate Swimming Speed, Hydrodynamic Drag and Energy Expenditure for Steller Sea Lions.

Forces due to propulsion should approximate forces due to hydrodynamic drag for animals horizontally swimming at a constant speed with negligible buoyancy forces. Propulsive forces should also correlate with energy expenditures associated with locomotion—an important cost of foraging. As such, biologging tags containing accelerometers are being used to generate proxies for animal energy expenditures despite being unable to distinguish rotational movements from linear movements. However, recent miniaturizations of gyroscopes offer the possibility of resolving this shortcoming and obtaining better estimates of body accelerations of swimming animals. We derived accelerations using gyroscope data for swimming Steller sea lions (Eumetopias jubatus), and determined how well the measured accelerations correlated with actual swimming speeds and with theoretical drag. We also compared dive averaged dynamic body acceleration estimates that incorporate gyroscope data, with the widely used Overall Dynamic Body Acceleration (ODBA) metric, which does not use gyroscope data. Four Steller sea lions equipped with biologging tags were trained to swim alongside a boat cruising at steady speeds in the range of 4 to 10 kph. At each speed, and for each dive, we computed a measure called Gyro-Informed Dynamic Acceleration (GIDA) using a method incorporating gyroscope data with accelerometer data. We derived a new metric—Averaged Propulsive Body Acceleration (APBA), which is the average gain in speed per flipper stroke divided by mean stroke cycle duration. Our results show that the gyro-based measure (APBA) is a better predictor of speed than ODBA. We also found that APBA can estimate average thrust production during a single stroke-glide cycle, and can be used to estimate energy expended during swimming. The gyroscope-derived methods we describe should be generally applicable in swimming animals where propulsive accelerations can be clearly identified in the signal—and they should also prove useful for dead-reckoning and improving estimates of energy expenditures from locomotion.

Kinematics of swimming and thrust production during powerstroking bouts of the swim frenzy in green turtle hatchlings.

ABSTRACTHatchling sea turtles emerge from nests, crawl down the beach and enter the sea where they typically enter a stereotypical hyperactive swimming frenzy. During this swim the front flippers are moved up and down in a flapping motion and are the primary source of thrust production. I used high-speed video linked with simultaneous measurement of thrust production in tethered hatchlings, along with high-speed video of free swimming hatchlings swimming at different water speeds in a swim flume to investigate the links between kinematics of front flipper movement, thrust production and swimming speed. In particular I tested the hypotheses that (1) increased swimming speed is achieved through an increased stroke rate; (2) force produced per stroke is proportional to stroke amplitude, (3) that forward thrust is produced during both the down and up phases of stroking; and (4) that peak thrust is produced towards the end of the downstroke cycle. Front flipper stroke rate was independent of water speed refuting the hypothesis that swimming speed is increased by increasing stroke rate. Instead differences in swimming speed were caused by a combination of varying flipper amplitude and the proportion of time spent powerstroking. Peak thrust produced per stroke varied within and between bouts of powerstroking, and these peaks in thrust were correlated with both flipper amplitude and flipper angular momentum during the downstroke supporting the hypothesis that stroke force is a function of stroke amplitude. Two distinct thrust production patterns were identified, monophasic in which a single peak in thrust was recorded during the later stages of the downstroke, and biphasic in which a small peak in thrust was recorded at the very end of the upstroke and this followed by a large peak in thrust during the later stages of the downstroke. The biphasic cycle occurs in ∼20% of hatchlings when they first started swimming, but disappeared after one to two hours of swimming. The hypothesis that forward thrust is produced during both the up and down stroke was only supported relatively rarely in hatchlings that exhibited the diphasic cycle, the majority of time forward thrust was only produced during the downstroke phase. The hypothesis that peak forward thrust is produced during the end of the downstroke was supported in both the monophasic and biphasic thrust producing stroke cycles.

Free-swimming northern elephant seals have low field metabolic rates that are sensitive to an increased cost of transport.

Widely ranging marine predators often adopt stereotyped, energy-saving behaviours to minimize the energetic cost of transport while maximizing energy gain. Environmental and anthropogenic disturbances can disrupt energy balance by prompting avoidance behaviours that increase transport costs, thereby decreasing foraging efficiency. We examined the ability of 12 free-ranging, juvenile northern elephant seals (Mirounga angustirostris) to mitigate the effects of experimentally increased transport costs by modifying their behaviour and/or energy use in a compensatory manner. Under normal locomotion, elephant seals had low energy requirements (106.5±28.2 kJ kg(-1) day(-1)), approaching or even falling below predictions of basal requirements. Seals responded to a small increase in locomotion costs by spending more time resting between dives (149±44 s) compared with matched control treatments (102±11 s; P<0.01). Despite incurred costs, most other dive and transit behaviours were conserved across treatments, including fixed, rhythmic swimming gaits. Because of this, and because each flipper stroke had a predictable effect on total costs (P<0.001), total energy expenditure was strongly correlated with time spent at sea under both treatments (P<0.0001). These results suggest that transiting elephant seals have a limited capacity to modify their locomotory behaviour without increasing their transport costs. Based on this, we conclude that elephant seals and other ocean predators occupying similar niches may be particularly sensitive to increased transport costs incurred when avoiding unanticipated disturbances.

Optimization of transit strategies while diving in foraging king penguins

AbstractOptimal foraging theories predict that air‐breathing, diving foragers should maximize time spent at feeding depths, and minimize time spent travelling between surface and depth (transits). The second part of this hypothesis was tested in free‐ranging king penguins Aptenodytes patagonicus using measurements of vertical speed, swimming speed, body angle and flipper stroke frequency during transits in relation to an index of foraging success (number of wiggles), during the bottom and the ascent phases of the dive. We found that, except for flipper stroke frequency, all measured variables increased with diving depth and foraging activity. The change in vertical speed was driven mainly by a change in body angle and a slight change in swimming speed. These results suggest a shortening of transit duration in response to increased foraging activity. Whereas the time spent commuting between the surface and foraging depths was reduced when foraging activity was high, vertical speed was only at its maximum over a small part of both ascent and descent phases of the dive. Within the first 10 m of descent, vertical speed increased with maximum dive depth and an index of foraging activity, suggesting that penguins anticipated their diving depth and foraging activity. Our results show that foraging king penguins adjust their diving behaviour in response to both diving depth and foraging activity. Further studies should consider ecological, physiological or mechanical constraints as factors that may limit foraging optimization.

Behaviour and Physiology: The Thermal Strategy of Leatherback Turtles

BackgroundAdult leatherback turtles (Dermochelys coriacea) exhibit thermal gradients between their bodies and the environment of ≥8°C in sub-polar waters and ≤4°C in the tropics. There has been no direct evidence for thermoregulation in leatherbacks although modelling and morphological studies have given an indication of how thermoregulation may be achieved.Methodology/Principal FindingsWe show for the first time that leatherbacks are indeed capable of thermoregulation from studies on juvenile leatherbacks of 16 and 37 kg. In cold water (< 25°C), flipper stroke frequency increased, heat loss through the plastron, carapace and flippers was minimized, and a positive thermal gradient of up to 2.3°C was maintained between body and environment. In warm water (25 – 31°C), turtles were inactive and heat loss through their plastron, carapace and flippers increased. The thermal gradient was minimized (0.5°C). Using a scaling model, we estimate that a 300 kg adult leatherback is able to maintain a maximum thermal gradient of 18.2°C in cold sub-polar waters.Conclusions/SignificanceIn juvenile leatherbacks, heat gain is controlled behaviourally by increasing activity while heat flux is regulated physiologically, presumably by regulation of blood flow distribution. Hence, harnessing physiology and behaviour allows leatherbacks to keep warm while foraging in cold sub-polar waters and to prevent overheating in a tropical environment.

Swimming depth and ocean currents affect transit costs in Steller sea lions Eumetopias jubatus

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 10:139-148 (2010) - DOI: https://doi.org/10.3354/ab00279 Swimming depth and ocean currents affect transit costs in Steller sea lions Eumetopias jubatus Allyson G. Hindle*, David A. S. Rosen, Andrew W. Trites Marine Mammal Research Unit, Fisheries Centre, AERL, University of British Columbia, 2202 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada *Email: allyson.hindle@gmail.com ABSTRACT: Transit costs associated with commuting between resting sites ashore and foraging areas at sea constitute an appreciable portion of foraging expenditures in pinnipeds. We examined transit swimming in 3 Steller sea lions Eumetopias jubatus trained to follow a moving boat at different speeds and depths. We measured dive behavior (duration) and focused specifically on activity measures (fore-flipper stroking and overall dynamic body acceleration [ODBA], an overall measure of body motion), which may be proxies for metabolic expenditure. Sea lions appeared to increase efficiency while transiting at depths that approached 3 times their body diameters (mean depth = 151 ± 1 cm SEM, n = 87). Although the response was not uniform for all tested scenarios, all of the observed significant adjustments to dive behavior and swimming mechanics supported an increased efficiency at this depth. An increase in transit speed (4.5 versus 3.5 knots [kn] surface speed) was associated with elevated flipper stroke frequencies (+5%) and stroke output (ODBA stroke–1, +48%). Sea lions transiting against the flow of a tidal current had reduced dive durations (–10%), while total ODBA was consistently elevated (+8% overall). This response to tidal flow was accompanied either by elevated ODBA stroke–1 (3.5 kn) or a parallel increase in stroking (4.5 kn). Our data demonstrate that small changes in the physical environment affect transiting in Steller sea lions, and imply that altered prey fields or changing ocean conditions can carry energetic consequences. KEY WORDS: Diving · Overall dynamic body acceleration · ODBA · Flipper stroking · Locomotion · Hydrodynamics · Foraging Full text in pdf format PreviousNextCite this article as: Hindle AG, Rosen DAS, Trites AW (2010) Swimming depth and ocean currents affect transit costs in Steller sea lions Eumetopias jubatus. Aquat Biol 10:139-148. https://doi.org/10.3354/ab00279 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 10, No. 2. Online publication date: August 24, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

Swimming for your life: locomotor effort and oxygen consumption during the green turtle (Chelonia mydas) hatchling frenzy

Swimming effort and oxygen consumption of newly emerged green turtle Chelonia mydas hatchlings was measured simultaneously and continuously for the first 18 h of swimming after hatchlings entered the water. Oxygen consumption was tightly correlated to swimming effort during the first 12 h of swimming indicating that swimming is powered predominantly by aerobic metabolism. The patterns of swimming effort and oxygen consumption could be divided into three distinct phases: (1) the rapid fatigue phase from 0 to 2 h when the mean swim thrust decreased from 45 to 30 mN and oxygen consumption decreased from 33 to 18 ml h(-1); (2) the slow fatigue phase from 2 to 12 h when the mean swim thrust decreased from 30 to 22 mN and oxygen consumption decreased from 18 to 10 ml h(-1); and (3) the sustained effort phase from 12 to 18 h when mean swim thrust averaged 22 mN and oxygen consumption averaged 10 ml h(-1). The decrease in mean swim thrust was caused by a combination of a decrease in front flipper stroke rate during a power stroking bout, a decrease in mean maximum thrust during a power stroking bout and a decrease in the proportion of time spent power stroking. Hence hatchlings maximise their swimming thrust as soon as they enter the water, a time when a fast swimming speed will maximise the chance of surviving the gauntlet of predators inhabiting the shallow fringing reef before reaching the relative safety of deeper water.

Acoustic determination of activity and flipper stroke rate in foraging northern fur seal females

Foraging effort for lactating female otariid pinnipeds is largely a function of the energy expended swimming to a site and diving in search of prey. This is especially true for northern fur seal Callorhinus ursinus females, which predictably punctuate their suckling with 7 to 12 d foraging trips at sea, with swimming distances often exceeding 400 km. In the present study we tested a unique approach (flow noise from onboard acoustic dataloggers) to empirically measure swim effort in free ranging female northern fur seals, the first such field measurements on an otariid pinniped. We first measured behavioural activity budgets of seals from a combination of satellite telemetry, pressure (depth), and onboard acoustic data. From these data we were able to quantify the time spent in each of 4 mutually exclusive forms of behaviour: locomoting, diving, resting, and surface activity. Second, flipper stroke rates and stroke rate patterns were measured from the acoustic data for each seal dur- ing 3 dive types (i.e. locomoting, shallow and mid/deep dives) and during 3 dive parts (descent, bot- tom time and ascent). Although stroke rates during each of the 3 dive types were similar (ca. 0.5 Hz), they were distinct during the different parts of a dive. In each case, variation among individuals was significant. Stroke rate patterns were distinct for the different dive types and dive parts. Overall, in addition to applying a unique technique to measure foraging effort in a declining population, the results emphasize the importance of accounting for individual variation to obtain accurate estimates of foraging cost.

TURNING MANEUVERS IN STELLER SEA LIONS (EUMATOPIAS JUBATUS)

AbstractSteller sea lions are highly maneuverable marine mammals (expressed as minimum turning radius). Video recordings of turns (n= 195) are analyzed from kinematic measurements for three captive animals. Speed‐time plots of 180° turns have a typical “V‐shape.” The sea lions decelerated during the first half of the turn, reached a minimum speed in the middle of the curved trajectory and reaccelerated by adduction of the pectoral flippers. The initial deceleration was greater than that for passive gliding due to pectoral flipper braking and/or change in body contour from a stiff, straight streamlined form. Centripetal force and thrust were determined from the body acceleration. Most thrust was produced during the power phase of the pectoral flipper stroke cycle. Contrary to previous findings on otariids, little or no thrust was generated during initial abduction of the pectoral flippers and during the final drag‐based paddling phase of the stroke cycle. Peak thrust force at the center of gravity occurs halfway through the power phase and the centripetal force is maximal at the beginning of the power stroke. Performance is modulated by changes in the duration and intensity of movements without changing their sequence. Turning radius, maximum velocity, maximum acceleration and turning duration were 0.3 body lengths, 3.5 m/s, 5 m/s2, and 1.6 s, respectively. The relative maneuverability based on velocity and length specific minimum turning radius is comparable to other otariids, superior to cetaceans but inferior to many fish.

Respiratory frequency, dive behaviour and social interactions of leatherback turtles, Dermochelys coriacea during the inter-nesting interval

We collected simultaneous dive Time Depth Recorder (TDR) data and video images from free swimming adult female leatherback turtles, Dermochelys coriacea, during the first 24 h after nesting on the beach, in order to determine relationships between dive parameters, activity, overall respiratory frequency and behaviour. We identified three different underwater locomotory activities (subsurface swimming, V-shaped dives and U-shaped dives) from video and TDR data that varied in their mean depth, duration and a number of other parameters. Overall respiratory frequency (overall f R) was significantly different between all locomotory activities, with turtles taking 1.7±0.1 breaths min −1 while subsurface swimming, 0.78 breaths min −1 after V-shaped dives and 0.57 breaths min −1 after U-shaped dives. Descent rates and ascent rates were significantly faster in U-shaped dives (descent 0.19±0.010 m s −1, ascent 0.28±0.015 m s −1) than in V-shaped dives (descent 0.10±0.008 m s −1, ascent 0.12±0.012 m s −1). Flipper stroke rates were significantly lower during the bottom component of U-shaped dives (0.18±0.02 strokes s −1) than during the descent (0.29±0.03 strokes s −1) or ascent (0.29±0.03 strokes s −1). From overall f R and flipper stroke rate data, we inferred that turtles used less energy during U-shaped dives than the other activity types. We recorded interactions between male turtles and the study females that lasted up to 11 min, during which male turtles displayed the characteristic courtship behaviour of sea turtles. It appeared that females attempted to avoid males by aborting ascent and extending dive duration to swim to the sea floor when males were present.