marine-mammal-research-newsletter

MARINE MAMMAL RESEARCH NEWSLETTER     |     Sept. 2014 (Issue 11)

This Just In


2014
 
Energetic linkages between short-term and long-term effects of whale watching disturbance on cetaceans: an example drawn from northeast Pacific resident killer whales.
Bain, D.E., R. Williams, and A.W. Trites. 2014.
In L. Bejder and R. Williams J. E. S. Higham (eds), Whale-watching, sustainable tourism and ecological management. Cambridge University Press, United Kingdom. pp. 206-228.
abstract
The core objective of efforts to understand and mitigate the effects of whale-watching has been to ensure the survival of populations. The first rigorous studies in the 1980s simply demonstrated that short-term behavioural responses existed. Managers, both in the private sector (whale-watch operators) and public sector responded with simple guidelines. Later studies showed some practices elicited stronger responses than others, and managers again responded with more effective guidelines to preclude activities that elicited strong evasive responses from killer whales. Recent work has shown that these guidelines are insufficient to prevent effects likely to be directly related to fitness (e.g. a reduction in foraging activity and increases in energy expenditure). As managers contemplate how to respond to such results, models such as ours can be constructed to address how short-term effects might relate to population dynamics, and whether data support a correlation between the quantity of exposure and shifts in population growth and decline. As better parameter estimates become available to inform these simple bioenergetics and population dynamics models, they should provide sufficient accuracy and precision to determine whether the effects of vessel traffic are sufficient to reduce the probability that the populations will survive in the long term (i.e. do they exceed potential biological removal (PBR)), or do the cumulative effects of whale watching and other human activities put the population in jeopardy of imminent extinction? The resident killer whales of the northeast Pacific represent an exceedingly data-rich case study of behavior and population biology, but they also represent an interesting study in management. The degree to which management is or is not precautionary determines how much evidence of population-level effects is needed before management actions are imposed. And as some of the science that has been done on this population is applied to other cetaceans, it is important to spell out another lesson learned— namely, that it is essential to specify quantitative management objectives that identify how much of an effect managers are willing to tolerate (limits of acceptable change, PBR and uncertainty:. Otherwise, the science can and will continue without serving any practical purpose as long as the whales persist.
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2014
 
Season and time of day affect the ability of accelerometry and the doubly labeled water methods to measure energy expenditure in northern fur seals (Callorhinus ursinus).
Dalton, A.J.M., D.A.S. Rosen and A.W. Trites. 2014.
Journal of Experimental Marine Biology and Ecology 452:125-136.
abstract
Estimates of energy expenditure for free-ranging animals are essential to answering a range of fundamental questions in animal biology, but are challenging to obtain and difficult to validate. We simultaneously employed three methods to measure the energy expenditure of 6 captive female northern fur seals (Callorhinus ursinus) during 5-day trials across 4 seasons: respirometry (oxygen consumption), doubly labeled water (DLW), and accelerometry. The DLW method estimated that the fur seals expended 13.1 ? 16.5% more energy than indicated by the more direct measures of oxygen consumption. Accelerometry failed to predict the average mass specific rate of oxygen consumption (VË™ O2DEE) within the individual seasons over entire 5- day trials. However, on a finer time scale (15 or 60 min) and adjusted for time of day, accelerometry estimated energy expenditure within an average difference of 5.4 ? 29.3% (60 min intervals) and 13.8 ? 39.5% (15 min intervals) of respirometry measured values. Our findings suggest that accelerometers have the potential to be more effective than the DLW method for measuring energy expenditure of free-ranging animals. However, rates of oxygen consumption varied with season, independent of overall activity. Seasonal effects (and time of day for accelerometry) must therefore be accounted for when estimating energy expenditure from measures of DLW and acceleration of free-swimming northern fur seals. Such corrections required for estimating energy expenditures in northern fur seals have implications for using accelerometers and DLW to estimate the energy expenditure of other species.

keywords     accelerometry, Callorhinus ursinus, daily energy expenditure, doubly labeled water, northern fur seal, respirometry
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2014
 
Broad thermal capacity facilitates the primarily pelagic existence of northern fur seals (Callorhinus ursinus).
Dalton, A.J.M., D.A.S. Rosen and A.W. Trites. 2014.
Marine Mammal Science 30:994-1013.
abstract
Thermoregulatory capacity may constrain the distribution of marine mammals despite having anatomical and physiological adaptations to compensate for the thermal challenges of an aquatic lifestyle. We tested whether subadult female northern fur seals (Callorhinus ursinus) experience increased thermoregulatory costs in water temperatures potentially encountered during their annual migration in the Bering Sea and North Pacific Ocean. Metabolic rates were measured seasonally in 6 captive female northern fur seals (2.75 to 3.5 yr old) in ambient air and controlled water temperatures of 2, 10, and 18 °C. Rates of oxygen consumption in ambient air (1 – 18 °C) were not related to environmental temperature except below 2.5 °C (winter only). However, metabolism was significantly higher during the fall seasonal trials (Sept – Oct) compared to other times of year, perhaps due to the costs of molting. The fur seals appeared thermally neutral in all seasons for all water temperat ures tested (2 – 18 °C) except during the summer when metabolic rates were higher in the 2 °C water. Comparing this broad thermal neutral zone to the average sea surface temperatures potentially encountered during annual migrations indicates wild fur seals can likely exploit a large geographic area without added thermal metabolic costs.
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2014
 
Short-term episodes of imposed fasting have a greater effect on young northern fur seals (Callorhinus ursinus) in summer than in winter.
Rosen, D. A. S., B. L. Volpov and A. W. Trites. 2014.
Conservation Physiology 2:1-9.
abstract
Unexpected shortages of food may affect wildlife differently depending on the time of year it occurs. We imposed 48-hr 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. Pre-fast metabolism of the fur seals while in ambient air or submerged in 4 ?C water was higher during summer (Jun-Sep) than winter (Nov-Mar), 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.
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2014
 
Thermal limits in young northern fur seals, Callorhinus ursinus.
Rosen, D.A.S. and A.W. Trites. 2014.
Marine Mammal Science 30(3):1014-1028.
abstract
The thermoregulatory abilities of northern fur seals (Callorhinus ursinus) during their first two years in the frigid waters of the North Pacific Ocean may limit their geographic distribution and alter the costs for exploiting different species of prey. We determined the thermoneutral zone of 6 young northern fur seals by measuring their metabolism in ambient air and controlled water temperatures (0-12 °C) from ages 8 to 24 mo. We found that the ambient air temperatures within our study (overall 1.5-23.9 °C) did not affect resting metabolic rates. Calculated lower critical temperatures in water varied between 3.9 and 8.0 °C, while an upper critical temperature in water was only discernible during a single set of trials. These thermal responses provide insight into the possible physiological constraints on foraging ecology in young northern fur seals, as well as the potential energetic consequences of ocean climate change and altered prey distributions.

keywords     Northern fur seal, Callorhinus ursinus, thermoregulation, metabolism, bioenergetics
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2014
 
Drag, but not buoyancy, affects swim speed in captive Steller sea lions.
Suzuki, I., K. Sato, A. Fahlman, Y. Naito, N. Miyazaki and A. W. Trites. 2014.
Biology Open 3:379-386.
abstract
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.
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2014
 
Lets go beyond taxonomy in diet description: testing a trait-based approach to prey-predator relationships.
Spitz, J., V. Ridoux and A. Brind'Amour. 2014.
Journal of Animal Ecology 83:1137-1148.
abstract
Understanding ‘Why a prey is a prey for a given predator?’ can be facilitated through trait-based approaches that identify linkages between prey and predator morphological and ecological characteristics and highlight key functions involved in prey selection.' Enhanced understanding of the functional relationships between predators and their prey is now essential to go beyond the traditional taxonomic framework of dietary studies and to improve our knowledge of ecosystem functioning for wildlife conservation and management. We test the relevance of a three-matrix approach in foraging ecology among a marine mammal community in the northeast Atlantic to identify the key functional traits shaping prey selection processes regardless of the taxonomy of both the predators and prey. Our study reveals that prey found in the diet of marine mammals possess functional traits which are directly and significantly linked to predator characteristics, allowing the establishment of a functional typology of marine mammal–prey relationships. We found prey selection of marine mammals was primarily shaped by physiological and morphological traits of both predators and prey, confirming that energetic costs of foraging strategies and muscular performance are major drivers of prey selection in marine mammals. We demonstrate that trait-based approaches can provide a new definition of the resource needs of predators. This framework can be used to anticipate bottom-up effects on marine predator population dynamics and to identify predators which are sensitive to the loss of key prey functional traits when prey availability is reduced.
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