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Steller sea
lion research > Open
water project > Past Present Future of project
OPEN WATER RESEARCH LAB – ANSWERING THE BIG QUESTIONS
 The Open Water Research Laboratory uses trained Steller sea lions to carry out studies in a natural environment. This allows scientists to answer questions that can not be addressed by studying animals in an aquarium or wild animals in the field. The sea lions at the Open Water facility can help answer important questions related to how much energy they use performing activities such as foraging for fish, and what physical and environmental factors affect those behaviors and related costs. The sea lions have been trained to repeatedly dive to depths of 10 to 50 m, which is similar to depths that sea lions dive to in the wild. After each dive they surface in a floating respirometry dome, which allows scientists to measure how much oxygen they consume and how much carbon dioxide they produce at the surface after every dive. This can then be converted into rates of energy use. Prey patches can be simulated by delivering fish via feeding tubes to different depths at varying rates. The sea lions are also trained to follow boats travelling at known speeds, or swim between distant targets at different depths. All of these behaviors can be undertaken while the sea lions carry an array of scientific instruments that collect detailed information. This unique set-up allows researchers to conduct controlled measurements away from the physical confines of a laboratory environment.
 Is diving expensive?
No, but be careful how you measure it!
Diving metabolic rate is the measure of the amount of energy sea lions use while diving. Sea lions use energy when diving, but they 'pay' for their dives when they resurface and replenish their oxygen stores. If you just measure the cost of each dive in a series, it would seem that the dive depth had a significant effect (Hastie et al 2006) and that, overall, sea lions used 40-45% less energy during dives than when they were just resting at the surface (Hastie et al 2007). This agrees with the observation that heart rate decreases ("bradycardia") in Steller sea lions during a dive (Young 2010). However, these results do not accurately represent the true costs because when the sea lions come to the surface between a series of dives, they are only partly refilling their oxygen tanks. The total cost of the dives is not really 'paid' (in terms of measured oxygen consumption) until the end of the series, when they have an extended recovery period at the surface. After taking this final recovery period into account, the cost of diving is no different than resting at the surface (Fahlman et al 2008a). That is still pretty remarkable, considering the amount of activity they undertake while foraging for fish.
 Does vertical swimming and horizontal diving cost the same?
No!
It might be tempting to think that diving is nothing more than vertical swimming, and therefore that the two activities cost the same. The difference is important to scientists that are trying to convert sea lion behavior into energy (and fish) requirements. The sea lions can be trained to swim a set distance at the water surface or dive to depth for the same distance. Initial results suggest that the cost of swimming at the surface is much higher than for diving for the same measured distance, as partly demonstrated by lower flipper stroke rates. This might explain the use of 'transit dives' observed in some species as an energy-saving behavior. The cost of swimming at the surface also depends on how close to the surface the sea lion was swimming. In theory, animals need to be at a certain depth to avoid additional swimming costs associated with swimming near the water surface. Sea lions that swim too near the surface must expend much more energy than when swimming deeper; they even have difficulty keeping up with the research boat at higher speeds!
 Can we measure costs in the field?
Yes!
When studying sea lions in the wild, it is impossible to directly measure how much oxygen they are consuming while diving. However, sea lions at the Open Water Research Lab are used to test and calibrate different methods that can estimate the amount of energy used by sea lions in the wild. They have helped to investigate whether measures of body movement (Overall Dynamic Body Acceleration; ODBA) can accurately measure energy use in sea lions (Fahlman et al 2008b). Other studies have determined that heart rate can be used to estimate energy expenditure of sea lions in the field, as long as diving and foraging behavior are taken into account (Young et al. 2010).
 Does prey patch quality affect foraging behavior?
Yes!
When does a sea lion give up on a shallow but meager prey patch, and head to deeper high quality patches? Scientists can answer this question by changing the speed at which fish come out of two feeding tubes (simulating different prey patches) that are positioned at different depths (10-40 m). It is easier, quicker, and cheaper for the sea lions to dive to the shallower tube. But at some point, the increased number of fish being delivered at the deeper tube becomes too tempting, and the sea lion will switch to the deeper tube. By altering the depths and rates of fish delivery, scientists can develop mathematical models that will predict the behavior of sea lions in the wild under a variety of circumstances.
 Does nutritional stress affect costs?
Yes!
Sea lions that are not obtaining sufficient food can invoke a number of physiological changes that can further affect their overall food requirements. For example, sea lions can use fat in their blubber layer as fuel during periods of nutritional stress. However, this fat also affects their buoyancy in the water, which may also affect the costs of diving for food. We tested this effect by experimentally altering the buoyancy of sea lions by attaching negatively and positively buoyant tubes to their harness and comparing the costs when they dove to set depths. We found that these artificial changes in body composition did not affect the diving metabolic rate of Steller sea lions (Fahlman et al 2008c). We propose that Steller sea lions may use other adjustments — such as diving lung volume — to compensate for changes in buoyancy to avoid additional metabolic costs. However, altering the buoyancy does not mirror all of the physiological changes that occur during nutritional stress. When sea lions were fasted in the summer and winter, their metabolic rate when resting at the surface decreased during both seasons, indicating that they were trying to save energy. However, the cost of diving actually increased in the winter, perhaps due to unavoidable higher thermoregulation costs. These results suggest that Steller sea lions are more sensitive to changes in body condition due to food shortages in the winter compared with the summer
Related Publications:
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Fasting affects the surface and diving metabolic rates of Steller sea lions (Eumetopias jubatus).
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Svärd, C., A. Fahlman, D.A.S. Rosen, R. Joy and A.W. and Trites. 2009.
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Aquatic Biology 8:71-82.
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abstract
Changes in metabolic rates were measured in 3 captive female Steller sea lions (Eumetopias jubatus) that experienced fasts during summer and winter. Metabolic rates were measured (via O2 consumption) before (MRs, surface) and after (DMR, dive + surface interval) the sea lions dove to 10–50 m depths. Measurements were obtained prior to 9-10 day fasts, and following a 14 day recovery period. The sea lions lost significantly more body mass (Mb) during the winter fast (10.6%), compared with the summer (9.5%). Mass-corrected dive metabolic rate (cDMR = DMR • Mb-0.714) was not affected by dive depth or duration, but increased significantly following the winter fasts (13.5 ± 8.1%), unlike the decrease during summer (-1.1 ± 3.2%). However, mass-corrected surface metabolic rate (cMRs) decreased significantly after both the summer (-16.4 ± 4.7%) and winter (-8.0 ± 9.0%) fasts. Consequently, the ratio between cDMR and cMRc was significantly higher in winter, suggestive of an increased thermal challenge and convective heat loss while diving. Increased cDMs following the fast indicated that digestion began during foraging and was not deferred, implying that access to ingested energy was of higher priority than optimizing diving ability. cDMR was elevated throughout the recovery period, independent of season, resulting in a 12% increase in foraging cost in winter and a 3% increase in summer. Our data suggest that Steller sea lions are more sensitive to changes in body condition due to food shortages in the winter compared with the summer.
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Metabolic costs of foraging and the management of O2 and CO2 stores in Steller sea lions.
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Fahlman, A., Svärd, C., Rosen, D.A.S., Jones, D.R. and Trites, A.W. 2008.
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Journal of Experimental Biology 211:3573-3580.
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abstract
The metabolic costs of foraging and the management of O2 stores during breath-hold diving was investigated in three female Steller sea lions (Eumetopias jubatus) trained to dive between 10 and 50 m (n=1142 dives). Each trial consisted of 2 to 8 dives separated by surface intervals (SI) that were determined by the sea lion (spontaneous trials) or by the researcher (conditioned trials). During conditioned trials, SI was long enough for O2 to return to pre-dive levels between each dive. The metabolic cost of each dive event (DMR = dive + surface interval) was measured using flow-through respirometry. The respiratory exchange ratio (VCO2 ·VCO2 -1) was significantly lower during spontaneous trials compared with conditioned trials. DMR was significantly higher during spontaneous trials and decreased exponentially with dive duration. A similar decrease in DMR was not as evident during conditioned trials. DMR could not be accurately estimated from the SI following individual dives that had short surface intervals (SI < 50 sec), but could be estimated on a dive by dive basis for longer SIs (SI > 50 sec). DMR decreased by 15%, but did not differ significantly from surface metabolic rates (MRS) when dive duration increased from 1 to 7 min. Overall, these data suggest that DMR is almost the same as MRS, and that Steller sea lions incur an O2 debt during spontaneous diving that is not repaid until the end of the dive bout. This has important consequences in differentiating between the actual and ‘apparent’ metabolic rate during diving, and may explain some of the metabolic differences reported between pinniped species.
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Buoyancy does not affect diving metabolism during shallow dives in Steller sea lions Eumetopias jubatus.
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Fahlman, A., G.D. Hastie, D.A.S. Rosen, Y. Naito and A.W. Trites. 2008.
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Aquatic Biology 3:147-154.
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abstract
hanges in buoyancy due to seasonal or abnormal changes in body composition are thought to significantly affect the energy budget of marine mammals through changes in diving costs. We assessed how changes in body composition might alter the foraging efficiency of Steller sea lions Eumetopias jubatus by artificially adjusting the buoyancy of trained individuals. PVC tubes were attached to harnesses worn by Steller sea lions that had been trained to feed at fixed depths (10 to 30 m) and to resurface inside a metabolic dome. Buoyancy was altered to simulate the naturally occurring differences in body composition reported in adult females (~12 to 26% subcutaneous fat). Diving characteristics (transit times and time at depth) and aerobic energy expenditure (gas exchange) were measured. We found that foraging cost decreased with the duration of the dive and increased with dive depth. However, changes in body composition did not affect the diving metabolic rate of Steller sea lions for dives between 10 and 30 m. We propose that Steller sea lions may adjust their diving lung volume to compensate for changes in buoyancy to avoid additional metabolic costs.
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Activity and diving metabolism correlate in Steller sea lion Eumetopias jubatus.
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Fahlman, A., R.Svärd,C. Wilson, D.A.S. Rosen and A.W. Trites. 2008.
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Aquatic Biology 2:75-84.
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abstract
Three Steller sea lions Eumetopias jubatus were trained to participate in free-swimming, open-ocean experiments designed to determine if activity can be used to estimate the energetic cost of finding prey at depth. Sea lions were trained to dive to fixed depths of 10 to 50 m, and to re-surface inside a floating dome to measure energy expenditure via gas exchange. A 3-axis accelerometer was attached to the sea lions during foraging. Acceleration data were used to determine the overall dynamic body acceleration (ODBA), a proxy for activity. Results showed that ODBA correlated well with the diving metabolic rate (dive + surface interval) and that the variability in the relationship (r2 = 0.47, linear regression including Sea lion as a random factor) was similar to that reported for other studies that used heart rate to estimate metabolic rate for sea lions swimming underwater in a 2 m deep water channel. A multivariate analysis suggested that both ODBA and dive
duration were important for predicting diving metabolic cost, but ODBA alone predicted foraging cost to within 7% between animals. Consequently,collecting 3-dimensional acceleration data is a simple technique to estimate field metabolic rate of wild Steller sea lions and other diving mammals and birds.
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Reductions in oxygen consumption during dives and estimated submergence limitations of Steller sea lions (Eumetopias jubatus).
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Hastie, G.D., D.A.S. Rosen and A.W. Trites. 2007.
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Marine Mammal Science 23:272-286.
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abstract
Accurate estimates of diving metabolic rate are central to assessing the energy
needs of marine mammals. To circumvent some of the limitations inherent with
conducting energy studies in both the wild and captivity, we measured diving
oxygen consumption of two trained Steller sea lions (Eumetopias jubatus) in the open
ocean. The animals dived to predetermined depths (5–30 m) for controlled periods
of time (50–200 s). Rates of oxygen consumption were measured using open-circuit
respirometry before and after each dive. Mean resting rates of oxygen consumption
prior to the dives were 1.34 (±0.18) and 1.95 (±0.19) liter/min for individual sea
lions. Mean rates of oxygen consumption during the dives were 0.71 (±0.24) and
1.10 (±0.39) liter/min, respectively. Overall, rates of oxygen consumption during
dives were significantly lower (45% and 41%) than the corresponding rates measured
before dives. These results provide the first estimates of diving oxygen consumption
rate for Steller sea lions and show that this species can exhibit a marked decrease in
oxygen consumption relative to surface rates while submerged. This has important
consequences in the evaluation of physiological limitations associated with diving
such as dive duration and subsequent interpretations of diving behavior in the wild.
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Studying trained Steller sea lions in the open ocean.
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Hastie, G, D.A.S. Rosen, and A.W. Trites. 2006.
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In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 193-204.
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abstract
The costs associated with diving are a central component of a sea lions? energy budget. Accurate estimates of diving costs are needed to assess energetic and physiological constraints on foraging behavior, including the potential effects of changes in prey distribution or density. However, information on sea lion diving physiology is limited to relatively few species of pinnipeds, and there is currently no information for Steller sea lions. Information on diving energetics of pinnipeds has traditionally been gathered using either wild or captive animals. However, studies with wild animals are logistically challenging and are limited by the opportunistic nature of data collection, whilst studies in captivity have been constrained by the physical restrictions of the holding facility. To circumvent some of these limitations, we combined the best aspects of both techniques by conducting diving metabolism studies with trained Steller sea lions in an open ocean environment. Two captive-reared Steller sea lions were housed in a holding pen and transported by boat to a diving trial area. The animals were trained to dive to predetermined depths for controlled periods of time using an underwater light targeting system and a video system to monitor behavior. At the end of each dive the sea lions returned to a respirometry dome on the surface where oxygen consumption was measured to estimate diving metabolism. This paper describes the experimental setup used to evaluate diving metabolism, discusses the logistical challenges of the study and the advantages of using such an approach to carry out physiological experiments with sea lions, and provides preliminary data on the diving energetics of Steller sea lions.
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The influence of depth on a breath-hold diver: predicting the diving metabolism of Steller sea lions (Eumetopias jubatus).
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Hastie, G.D, D.A.S. Rosen, A.W. Trites. 2006.
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Journal of Experimental Marine Biology and Ecology 336:163-170.
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abstract
Diving animals must endeavor to increase their dive depths and prolong the time they spend exploiting resources at depth. Results from captive and wild studies suggest that many diving animals extend their foraging bouts by decreasing their metabolisms while submerged. We measured metabolic rates of Steller sea lions (Eumetopias jubatus) trained to dive to depth in the open ocean to investigate the relationships between diving behaviour and the energetic costs of diving. We also constructed a general linear model to predict the oxygen consumption of sea lions diving in the wild. The resultant model suggests that mean swimming distance and depth of dives significantly influence the oxygen consumption of diving Steller sea lions. The predictive power of the model was tested using a cross-validation approach, whereby models reconstructed using data from pairs of sea lions were found to accurately predict the oxygen consumption of the third diving animal. Predict!
ed oxygen consumption during dives to depth ranged from 3.37 L min-1 at 10 meters, to 1.40 L min-1 at 300 meters over a standardized swimming distance of 600 meters. This equated to an estimated metabolic rate of 97.54 and 40.52 MJ day-1, and an estimated daily feeding requirement of 18.92 and 7.96 kg day-1 for dives between 10 and 300 meters, respectively. The model thereby provides information on the potential energetic consequences that alterations in foraging strategies due to changes in prey availability could have on wild populations of sea lions.
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