Dive Cycle Research Articles

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.

Structure and dynamics of minke whale surfacing patterns in the Gulf of St. Lawrence, Canada.

Animal behavioral patterns can help us understand physiological and ecological constraints on animals and its influence on fitness. The surfacing patterns of aquatic air-breathing mammals constitute a behavioral pattern that has evolved as a trade-off between the need to replenish oxygen stores at the surface and the need to conduct other activities underwater. This study aims to better understand the surfacing pattern of a marine top predator, the minke whale (Balaenoptera acutorostrata), by investigating how their dive duration and surfacing pattern changes across their activity range. Activities were classified into resting, traveling, surface feeding and foraging at depth. For each activity, we classified dives into short and long dives and then estimated the temporal dependence between dive types. We found that minke whales modified their surfacing pattern in an activity-specific manner, both by changing the expression of their dives (i.e. density distribution) and the temporal dependence (transition probability) between dive types. As the depth of the prey layer increased between activities, the surfacing pattern of foraging whales became increasingly structured, going from a pattern dominated by long dives, when feeding at the surface, to a pattern where isolated long dives were followed by an increasing number of breaths (i.e. short dives), when the whale was foraging at depth. A similar shift in surfacing pattern occurred when prey handling time (inferred from surface corralling maneuvers) increased for surface feeding whales. The surfacing pattern also differed between feeding and non-feeding whales. Resting whales did not structure their surfacing pattern, while traveling whales did, possibly as a way to minimize cost of transport. Our results also suggest that minke whales might balance their oxygen level over multiple, rather than single, dive cycles.

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.

Sex differences in risk perception in deep‐diving bottlenose dolphins leads to decreased foraging efficiency when exposed to human disturbance

Summary Individuals make behavioural decisions by weighing potential advantages and costs (e.g. increased food intake vs. increased risk of predation). When animals change their activities in response to a perceived threat, their energetic input may decline. Marine ecotourism, including whale and dolphin watching, is growing globally and cetaceans perceive interactions with tour vessels as a form of risk. Observable behavioural changes need to be linked to bioenergetic effects to determine the potential population consequences of this disturbance. We developed a theoretical optimal dive model for bottlenose dolphins under three potential types of perceived risk resulting from human interactions at the surface (decreasing instantaneous risk, increasing instantaneous risk and no risk). We compared the predictions of these theoretical models to observed dive cycles of foraging male and female dolphins in the presence and absence of tour vessels. We used mixture models to classify dive types and mixed effects models to analyse changes in the interbreath interval of surface and bottom dives and the frequency of estimated bottom dives. Males significantly increased bottom time and performed fewer bottom dives when boats were present, matching predictions of our theoretical model for perceived decreasing instantaneous risk. In contrast, females significantly decreased bottom times and increased the frequency of bottom dives, matching predictions from the model for perceived increasing instantaneous risk. Therefore, our empirical results suggest differences in the perception of risk between sexes. Synthesis and applications. By comparing theoretical predictions with observed dive data, our study suggests that boat interactions during foraging can cause decreased net energy gain over a foraging bout for both sexes, with females being more impacted. The population under study is currently listed as critically endangered. Understanding whether these predicted energetic impacts affect an individual's vital rates will provide a link to the population‐level consequences of this disturbance. Previous analytical approaches have failed to capture the costs associated with disturbance during foraging, leading to management recommendations that only protect animals from increased energetic expenditure. We suggest that the current management scheme should be revised to include foraging areas in order to secure the energy intake of animals.

Decreasing the radiated acoustic and vibration noise of both prop-driven and buoyancy-driven autonomous underwater vehicles

Our previously published results from decreasing the radiated acoustic and vibration noise of a mid-size, prop-driven autonomous underwater vehicle (AUV) show self noise levels recorded at sea by an AUV-mounted hydrophone array that are at, or below, typical background ocean noise levels across the frequency band above 200 Hz. The remaining noise below 200 Hz is primarily vibration induced. The modifications required to achieve this 20–50 dB reduction in propulsion and steering system noise levels will be reviewed in this talk. In addition, at-sea measurements of the acoustic noise radiated by the large (30 L) buoyancy engine on a 20-ft wing span flying wing autonomous underwater glider are presented. Whereas a prop-driven system operates continuously, the buoyancy-driven propulsion system has a very low duty cycle of a few percent; it is on only for about 3 min during each dive cycle. Onboard self noise from the glider's internal fluid-based roll control system far exceeds that from an aileron-based system. However, the former system provides control authority at or near neutral buoyancy. [Work supported by the Office of Naval Research and BP.]

Analysis on Hybrid Effects of Parallel Pneumatic Hybrid Vehicle

To reveal the potential and means of energy saving and emission reduction for the parallel pneumatic hybrid vehicle (PHV) proposed in this article, the comparison analysis between parallel PHV and conventional diesel vehicle (CDV) was made on the dive cycles of NEDC, UDDS, HWFET and JAPAN10-15 using the mathematic model. The results show: For the drive cycles of NEDC, UDDS, HWFET and JAPAN10-15, the PHV could decrease emissions by 58.84%, 38.76%, 14.54%, and 66.59% and save energy by 13.12%, 14.06%, -6.27% and 28.06% respectively com-pared to the CDV; Of the five hybrid means of shutting down the ICE at idle, regenerative braking, optimizing working area of ICE, using the exhaust heat of ICE and downsizing ICE, using the ex-haust heat of ICE along with shutting down the ICE at idle have the most impact on energy saving, and then is the downsizing ICE, but using exhaust heat would increase energy consumption; Opti-mizing working area of ICE and shutting down the ICE at idle have the greatest contribution to re-duction emissions, followed is also downsizing ICE. The efficiency of regenerative braking is very low, as well as the heat exchange efficiency of the adopted heat exchanger, requiring further opti-mization and design.

Foraging dives of sperm whales in the north-western Mediterranean Sea

Oceanic odontocetes rely on echolocation to forage on pelagic or benthic prey, but their feeding ecology is difficult to study. We studied sperm whale foraging dives during summer in the north-western Mediterranean, using visual and passive acoustic observations. Clicking and creaking activities were recorded during dives of focal whales, at distances <3000 m using a towed hydrophone and DAT recorder. A total of 52 sperm whales were recorded over at least one full dive cycle. Data were obtained for 156 complete dives in total, including sequences of up to nine consecutive dives. Various dive and environmental variables were entered in multiple linear regression and principal components analysis, as well as estimated mass of whales. Creak rate was 0.80 creak/minute on average, with moderate variance. Bigger whales tended to dive longer at greater depths (as suggested by ascent durations), and emitted more creaks during a dive: 20.2 creaks/dive on average for individuals <24 tons, compared to 25.6 creaks/dive for animals >24 tons of estimated mass. For individual whales, creak rates did not vary significantly with size (range 0.78–0.80 creak/minute), but decreased with time of the day, and increased for shorter foraging phases. For different dives, higher creak rates were also observed earlier in the day, and linked to shorter foraging phases and surface durations. Although the exact significance of creak emissions (i.e. foraging attempt or prey capture) is not precisely determined, creak rates may be reliably used to quantify sperm whale foraging when single animal dives can be followed acoustically.

Differences in Diving Behaviour Optimality May Cause Differences in Reproductive Success in Chinstrap Penguins: A Cases Study

Bio-logging is a useful technique for obtaining information on foraging behaviour, physiology, and environ- mental conditions from animals in marine ecosystems. By integrating this information, researchers can investigate the ecology of general prey-predator system in terms of their behaviour with the help of theoretical models. In the present study, I analyse the diving behaviour of two chinstrap penguins using an index of diving behaviour optimality as a case study. Because of small sample size in the study, I demonstrate possibility to prove the association between calcu- lated optimality index and breeding success in birds and how it basically would be possible if more individuals would be included in analyses. This index is the proportion of observed dive time to standard dive time. Standard dive time is de- fined as an optimal dive time that maximises the proportion of bottom time to the duration of a dive cycle for a given travel time. Using this index, I found a difference in the optimality of diving behaviour and prey conditions experienced between birds, which may cause differences in chick growth rate. Because many dives have already been recorded using bio-logging techniques, using this index to analyse diving behaviour could give new insights into the foraging ecology of top predators in marine ecosystems.

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.

WHEN, AND WHEN NOT, TO ESTIMATE METABOLISM FROM HEART RATE

Energy is the currency of life and knowing how much organisms use as they go about their daily activities is essential for ecologists wishing to understand the complex interactions underpinning ecosystems. However, estimating energy consumption is far from straightforward, and most of the current methods have drawbacks. Beth Young and her colleagues from the University of British Columbia and Vancouver Aquarium, Canada, explain that many scientists convert heart rate measurements collected from active animals into energy expenditure. However, the calculation is based on measurements taken from animals in laboratory settings and the team says, ‘The artificial modes of locomotion and environments employed in these studies raise questions of applicability to animals that spend considerable time diving to depth.’ Curious to find out how reliable these estimates are for diving animals in their natural surroundings, Young and her colleagues measured the heart and oxygen consumption rates of Stellar sea lions foraging in open water and tested whether heart rate could predict an animal's diving and average metabolic rates (p. 2267).Training three sea lions to make a sequence of dives for fish to depths of 10 and 40 m, the team found that heart rate was a good indicator of average metabolic rate over a single dive and a series of dives, including the time spent at the surface catching their breath. However, heart rate was not a good indicator of the sea lion's metabolic rate during the dive.Also, the team found that the equations that they derived to predict oxygen consumption from heart rate were different for multiple dives and single dives. For single dives the equation was essentially the same as that for resting sea lions. However, the animals that dived repeatedly consumed more oxygen per heartbeat than the single divers, presumably because they accumulated a greater oxygen debt.So, heart rate measurements can be used to estimate average metabolic rate in diving sea lions, but only over complete dive cycles where the recovery period is also included. The team admits, ‘Logistically, it is not always possible to distinguish single recovery dive cycles from dive bout cycles in free-ranging animals,’ and recommends that physiologists calculate the average metabolic rate over a dive bout to provide the most accurate metabolic rate estimates.

Interpreted acoustic ocean observations from Argo floats.

While it is technically possible to record high bandwidth ambient noise, practically the ocean ambient sound data need to be subsampled and interpreted for users. A new configuration of Argo float has been augmented with passive aquatic listener (PAL) technology to monitor the ocean ambient sound during the drift phase of the Argo float mission, typically at 1000 m depth for 10 days at a time. These ocean ambient sound data are interpreted as wind speed, rainfall rate, and marine animal detections. These data are reported to users via two-way iridium satellite communication link when the float surfaces at the end of each dive cycle. Changes in sampling strategies can be implemented if desired. The first set of these floats has been deployed and additional deployments are ongoing. The data will be used to study the fresh water cycle of the ocean as part of the NASA Aquarius/SAC-D satellite mission scheduled to be launched this year.

Assessing the Validity of the Accelerometry Technique for Estimating the Energy Expenditure of Diving Double-Crested CormorantsPhalacrocorax auritus

Over the past few years, acceleration-data loggers have been used to provide calibrated proxies of energy expenditure: the accelerometry technique. Relationships between rate of oxygen consumption and a derivation of acceleration data termed "overall dynamic body acceleration" (ODBA) have now been generated for a range of species, including birds, mammals, and amphibians. In this study, we examine the utility of the accelerometry technique for estimating the energy expended by double-crested cormorants Phalacrocorax auritus to undertake a dive cycle (i.e., a dive and the subsequent pause at the surface before another dive). The results show that ODBA does not calibrate with energy expenditure in diving cormorants, where energy expenditure is calculated from measures of oxygen uptake during surface periods between dives. The possible explanations include reasons why energy expenditure may not relate to ODBA but also reasons why oxygen uptake between dives may not accurately represent energy expenditure during a dive cycle.

Foraging behaviour and diving pattern of Little Cormorant Phalacrocorax niger (Vieillot) (Pelecaniformes: Phalacrocoracidae) at Kallampara backwaters, Kerala, India

The foraging behaviour and diving patterns of Little Cormorant Phalacrocorax niger were studied during August 2005 to March 2006 by direct observation of individuals foraging at Kallampara River (11009’25.5”N & 75051’02.0”E), near the Kadalundy Bird Sanctuary, Kozhikode District, Kerala, India. The individuals observed, foraged solitarily in shallow waters and displayed relatively short diving bouts composed of several dives (25.3 � plus or minus 5.75). The dive duration was positively related to surface resting time. Also, duration of dives decreased with increase in the number of dive cycles per bout. The mean diving efficiency was within the range reported for Phalacrocoracidae. Little Cormorants are opportunistic foragers utilizing the availability of prey to the maximum depending on tidal cycles. This study shows a specific relation between body mass, dive duration and diving efficiency.

Predator-induced modifications to diving behavior vary with foraging mode

Breath-hold divers are strongly interacting species whose top – down infl uence on aquatic communities is shaped by factors governing their diving decisions. Although some of these factors (e.g. physiological constraints, energetic needs) have been scrutinized, the possibility that predation risk infl uences diving behavior has been largely overlooked, and no study to date has asked if anti-predator responses by divers depend on foraging mode. We contrasted dive cycle changes by herbivorous dugongs Dugong dugon using two foraging tactics – cropping, which always permits anti-predator vigilance, and excavation, which limits surveillance at depth – in response to temporal variation in tiger shark Galeocerdo cuvier abundance. Dugongs responded to increasing shark abundance (one component of predation risk) by diving more frequently without changing their surface times and thereby spending a greater proportion of time at the surface, but only while excavating. When threatened, in other words, excavating dugongs sacrifi ced foraging time at depth to facilitate shark detection. In contrast, cropping dugongs at risk from sharks were able to continue diving and foraging normally. By implication, future studies should consider the infl uence of predation risk on diving decisions, even by large-bodied species, and the possibility that behavioral responses by divers to predators may vary with foraging mode.

Women from Venus, men from Mars: inter‐sex foraging differences in the imperial cormorant Phalacrocorax atriceps a colonial seabird

Colonial seabirds are central place foragers and likely to be subject to substantial competition for resources. Mechanisms proposed for reducing intra‐specific competition include differential inter‐sex area use mediated by adult choice. We used GPS loggers and dive recorders to study area use and dive depth in a total of 27 male and 26 female imperial cormorants Phalacrocorax atriceps breeding at a colony of some 6500 birds at Punta Leon, Chubut, Argentina during 2004 and 2005. Although time spent travelling and distances between the colony and foraging sites were similar for both sexes, males and females travelled away from their colony using routes virtually perpendicular to each other so that their foraging areas were distinctly different; females hunted close to the coast while males foraged offshore in deeper water. Consideration of foraging efficiency underwater, defined as the duration spent on the bottom divided by the dive cycle duration, showed that females were more efficient at depths < 40 m while males more efficient at depths > 40 m. We suggest that the substantial sexual dimorphism in this species may be responsible for the different depth‐linked foraging efficiencies and that selection for appropriate depths could lead to differential habitat use and putative differences in prey selection.

Humpback whale song on the Western Antarctic Peninsula feeding ground.

Humpback whale song is a complex and highly stereotyped acoustic display believed to be associated with breeding activities. The song has primarily been recorded from male whales on the low‐latitude breeding grounds, though singing has also been documented on some feeding grounds during late fall and early spring using stationary passive acoustic recorders. Here, the song was documented with animal‐bourne tags in a relatively unstudied population of humpback whales along the Western Antarctic Peninsula feeding ground during late fall (May and June). DTAGs were attached for 24‐h periods to six whales in 2009 and eight whales in 2010 to record sound production and body orientation. Song chorusing has been present on all tag acoustic records analyzed to date, and multiple whales tagged in 2010 were actively singing. Song bouts in the 2010 records were generally less than one dive cycle in duration and were often surrounded by periods of social sound production. This is the first description of humpback whale song in the Antarctic, and its frequent occurrence is indicative of the amount of social activity on this feeding ground. These data suggest that humpback whale mating cycles may be more driven by season than by physical location.

When foraging becomes unprofitable: energetics of diving in tidal currents by common eiders wintering in the Arctic

A variety of ecological, physiological and environmental factors influence the energy budgets of diving animals. For common eiders Somateria mollissima sedentaria wintering in sea ice habitats in the Canadian Arctic, time and energy costs of diving increase exponentially with tidal cur- rent speed. Here we use literature estimates of diving energetics and underwater dive data to quan- titatively model net energy gain per dive cycle as a function of current speed. The model indicates a strong non-linear decrease in the profitability of diving with increasing currents, predicting that net energy gain per dive cycle will reach zero and become unprofitable at 1.21 m s -1 (at 11.3 m depth using baseline parameters from our study). As currents increase travel time, foraging time at the bot- tom decreases non-linearly, reaching a point where intake is inadequate to balance increasing div- ing and surface swimming costs. Sensitivity analysis indicates that this threshold is robust over a range of energy expenditure rates and is influenced most by energy intake rate, emphasising the importance of ecological factors such as prey abundance and quality. Eiders stop foraging and rest on the ice well below this threshold in weaker current regimes (~0.8 m s -1 ), at about the point when prof- itability begins to decelerate. Behavioural time series of diving under constraints of strong tidal cur- rent regimes indicate that these eiders do occasionally dive in currents up to ~1.2 m s -1 , providing support for the energetic model. Eiders did not dive in faster currents, which could also be influenced by a physiological limit to swimming speed. We conclude that ocean currents can cause a non-linear decrease in net energy balance and are therefore an important and understudied consideration for diving animals. Many functional aspects of diving (e.g. locomotor costs or convective heat loss) have non-linear characteristics; these diminishing returns can be expected to play an important role in the dynamics of behavioural routines and the ability of organisms to respond to environmental variation.

Dive efficiency versus depth in foraging emperor penguins

Dive duration generally decreases with dive depth in air-breathing vertebrates. In most penguin species, this occurs due to increasing transit (descent and ascent) durations. However, in U-shaped dives, this is also because the duration of the bottom phase of the dive increases with increasing depth. We considered the time-based efficiency with which birds can use different diving depths by using depth recorders on 9 foraging emperor penguins Aptenodytes forsteri, studied dur- ing the early and late chick-rearing period in Adelie Land, Antarctica. Dive and post-dive duration positively correlated with diving depth, but particularly long recovery durations were apparent for dives longer than 456 s. This inflection point (i.e. 456 s) corresponded to a theorized maximum rate of gain of prey per dive cycle. By using the number of undulations in the bottom phase of the dive as a proxy for prey capture success, we conclude that the most lucrative dive depths for the birds studied were between 50 and 225 m. Since these depths were also those most often visited, we think that foraging emperor penguins focus on depths where profitability is highest.

Environmental and ecological factors influencing dive behaviour in the freshwater snake Acrochordus arafurae: a field-based telemetric study

Acrochordus arafurae is a fully aquatic, freshwater snake distributed throughout tropical Australia. To better understand the ecological factors influencing their behavioural repertoire, we remotely monitored field body temperature and diving in snakes free-ranging within their natural habitat. The body temperatures of A. arafurae exhibited a diel profile similar to the surface water temperature, and reflected the high proportion of time that snakes remained <1 m from the surface. The average dive depth was 0.62 m and 95% of dives had an average depth of 1 m or less. Snakes occasionally ventured into deeper water (>6 m), and there was a positive correlation between dive depth and duration. Average dive duration was 6.6 min and 84% of dives were terminated within 10 min, but all snakes performed dives >50 min during the 14-day observation period. We hypothesise that the dive behaviour was strongly influenced by predation pressure. The snakes partake in short dives within the aerobic dive limit to reduce the amount of time they need to spend at the surface on each breathing bout, reducing the risk of predation by birds. Predation is a strong selective force that might alter the time allocation during dive cycles.

The influence of temperature on diving behaviour in the alpine newt, Triturus alpestris

An aquatic lifestyle poses serious restriction to air-breathing animals in terms of time and energy spent during a dive cycle. The diving frequency increases with water temperature, therefore an ectotherm's time budget greatly depends on the thermal characteristics of the aquatic environment. Available data suggests that time costs caused by temperature-dependent dive frequency can be partially compensated for by adjusting the swimming speed and diving angle during dive cycle. We tested this prediction by examining the influence of temperature on the diving behaviour of the alpine newt, Triturus alpestris. The ascending speed and angle showed disparate patterns of temperature dependency, with a minor influence on travel duration. Surprisingly, at higher temperatures, the diving newts saved most of their time by restricting swimming activity in the water column during their return to the bottom and not by adjusting their ascending duration. Hence, aquatic newts have the capacity to reduce temperature-dependent time costs of aerial breathing primarily by behavioural modifications during the descending phase of the dive cycle.