Foraging Behavior and Success of a Mesopelagic Predator in the Northeast Pacific Ocean: Insights from a Data-Rich Species, the Northern Elephant Seal

The mesopelagic zone of the northeast Pacific Ocean is an important foraging habitat for many predators, yet few studies have addressed the factors driving basin-scale predator distributions or inter-annual variability in foraging and breeding success. Understanding these processes is critical to reveal how conditions at sea cascade to population-level effects. To begin addressing these challenging questions, we collected diving, tracking, foraging success, and natality data for 297 adult female northern elephant seal migrations from 2004 to 2010. During the longer post-molting migration, individual energy gain rates were significant predictors of pregnancy. At sea, seals focused their foraging effort along a narrow band corresponding to the boundary between the sub-arctic and sub-tropical gyres. In contrast to shallow-diving predators, elephant seals target the gyre-gyre boundary throughout the year rather than follow the southward winter migration of surface features, such as the Transition Zone Chlorophyll Front. We also assessed the impact of added transit costs by studying seals at a colony near the southern extent of the species’ range, 1,150 km to the south. A much larger proportion of seals foraged locally, implying plasticity in foraging strategies and possibly prey type. While these findings are derived from a single species, the results may provide insight to the foraging patterns of many other meso-pelagic predators in the northeast Pacific Ocean

Bioenergetics of marine mammals: the influence of body size, reproductive status, locomotion and phylogeny on metabolism

Metabolic energy demand is both a cause and consequence of how animals interact with their environments. Describing patterns of metabolism and understanding the drivers underscoring those patterns have been long-standing goals of biology for almost a century. Mammals are often the subject of comparative metabolism studies, and it is clear that their metabolic rates are determined by a complex interaction between a host of morphological, ecological, behavioral and evolutionary factors. In contrast, metabolism is often considered to be less complex for marine mammals, that is, uniformly high across all groups. This perception is the result of a paradigm that took root when determinations on marine mammals were relatively rare, and it has persisted despite a growing number of studies reporting low to moderate metabolic rates in some species. In the following chapters, I describe the foraging energetics of free-swimming northern elephant seals (Mirounga angustirostris) and show that these seals have extremely low field metabolic rates (FMRs) that do not conform to traditional expectations for marine mammals. I also demonstrate the effects of body size and reproductive status on the bioenergetics of this species, showing that larger, fatter, pregnant seals have lower FMRs and higher foraging success. I also am able to demonstrate the importance of locomotory efficiency in maintaining a low FMR: seals responded to artificially increased locomotion costs by increasing their swimming efforts, thereby increasing FMR and lowering foraging success. These results demonstrate the sensitivity of elephant seals to anthropogenic disturbance in important foraging grounds, and potentially along migration corridors.These results also demonstrate an energy economy strategy in a species that, by virtue of its shared environment with other marine mammals, would traditionally be predicted to have an elevated metabolic rate. In my last data chapter, I revisit the paradigm underscoring these traditional predictions. I synthesize all mammalian metabolic determinations published to–date and am able to show that the metabolic rates of marine mammals are comparable to those of terrestrial mammals, particularly when they are compared to other carnivores. I also discuss the importance of differences between the various marine mammal groups in their ecologies, behaviors and evolutionary histories in determining metabolic energy demand. These results suggest that metabolism in marine mammals is as complex as in other mammals, and that the assumption of one uniform, high–energy group is not supported by the data. This has important implications for managers interested in predicting the prey requirements of these upper trophic level predators, as traditional models are likely to exaggerate the impact of many species on their environments

Analysis of North Atlantic Right Whale Swimming Behavior during Bottom Foraging Events to Assess Entanglement Risk

The western North Atlantic right whale, Eubalaena glacialis, is critically endangered throughout its range. With approximately 300 individuals remaining, this population suffers significant impacts from entanglement in commercial fishing gear that are impeding the species’ ability to recover from historic hunting pressures. The purpose of this study was to evaluate the circumstances surrounding serious entanglements. Data collected from foraging right whales tagged in 2001 and 2002 were analyzed to identify behavior(s) that may increase the risk of entanglement in certain types of gear at certain depths. Results suggest that foraging right whales display ‘risky’ behaviors that may increase their chances of becoming entangled, including swimming at depths where floating loops of line from bottom-fixed gear extend into the water column, and increased rolling behavior through vertical line during the ascent and descent portions of the dive cycle. This work could contribute to current conservation efforts on behalf of the whale by informing the design of more 'whale-friendly'’ fishing gear, as well as help managers determine more effective mitigation strategies to reduce the risk that fishing gear poses to right whales

Drinking Behavior and Perception of Thirst in Untrained Women During 6 Weeks of Heat Acclimation and Outdoor Training

The purposes of this study were to characterize measures of fluid intake and perception of thirst in women over a 6-week period of exercise-heat acclimation and outdoor training and examine if this lengthy acclimation period would result in changes in fluid intake that differ from those previously reported in men utilizing a shorter acclimation protocol of 8-10 days. Voluntary water intake (11- 17 degreesC) and perception of thirst were measured in a group of 5 women (21-26 yr) undergoing exercise-heat acclimation for 90 min/day, 3 day s/wk (3 6 degreesC, rh 50-70%) and outdoor training 3 days/wk for 6 weeks. Decreased drinking during acclimation was characterized by a decrease in the number of drinks (35 +/- 10 to 17 +/- 5;p \u3c .05), greater time to first drink (9.9 +/- 2.0 to 23.1 +/- 4.7 min; p \u3c .05), and a decrease in total volume ingested per week (3310 +/- 810 to 1849 +/- 446 ml;p \u3c .05) through the 6-week study. Mean perceived thirst measurements remained low and showed only slight variance 3 +/- 0.4 to 5 +/- 0.4). These observations support a psycho-physiological response pattern different than that previously observed during 8-10 day acclimation protocols in men

The foraging benefits of being fat in a highly migratory marine mammal

Foraging theory predicts that breath-hold divers adjust the time spent foraging at depth relative to the energetic cost of swimming, which varies with buoyancy (body density). However, the buoyancy of diving animals varies as a function of their body condition, and the effects of these changes on swimming costs and foraging behaviour have been poorly examined. A novel animal-borne accelerometer was developed that recorded the number of flipper strokes, which allowed us to monitor the number of strokes per metre swam (hereafter, referred to as strokes-per-metre) by female northern elephant seals over their months-long, oceanic foraging migrations. As negatively buoyant seals increased their fat stores and buoyancy, the strokes-per-metre increased slightly in the buoyancy-aided direction (descending), but decreased significantly in the buoyancy-hindered direction (ascending), with associated changes in swim speed and gliding duration. Overall, the round-trip strokes-per-metre decreased and reached a minimum value when seals achieved neutral buoyancy. Consistent with foraging theory, seals stayed longer at foraging depths when their round-trip strokes-per-metre was less. Therefore, neutrally buoyant divers gained an energetic advantage via reduced swimming costs, which resulted in an increase in time spent foraging at depth, suggesting a foraging benefit of being fat

Comparisons and Uncertainty in Fat and Adipose Tissue Estimation Techniques: The Northern Elephant Seal as a Case Study.

Fat mass and body condition are important metrics in bioenergetics and physiological studies. They can also link foraging success with demographic rates, making them key components of models that predict population-level outcomes of environmental change. Therefore, it is important to incorporate uncertainty in physiological indicators if results will lead to species management decisions. Maternal fat mass in elephant seals (Mirounga spp) can predict reproductive rate and pup survival, but no one has quantified or identified the sources of uncertainty for the two fat mass estimation techniques (labeled-water and truncated cones). The current cones method can provide estimates of proportion adipose tissue in adult females and proportion fat of juveniles in northern elephant seals (M. angustirostris) comparable to labeled-water methods, but it does not work for all cases or species. We reviewed components and assumptions of the technique via measurements of seven early-molt and seven late-molt adult females. We show that seals are elliptical on land, rather than the assumed circular shape, and skin may account for a high proportion of what is often defined as blubber. Also, blubber extends past the neck-to-pelvis region, and comparisons of new and old ultrasound instrumentation indicate previous measurements of sculp thickness may be biased low. Accounting for such differences, and incorporating new measurements of blubber density and proportion of fat in blubber, we propose a modified cones method that can isolate blubber from non-blubber adipose tissue and separate fat into skin, blubber, and core compartments. Lastly, we found that adipose tissue and fat estimates using tritiated water may be biased high during the early molt. Both the tritiated water and modified cones methods had high, but reducible, uncertainty. The improved cones method for estimating body condition allows for more accurate quantification of the various tissue masses and may also be transferrable to other species

Difference in sculp ultrasound thickness comparing ultrasounds with and without an image for dorsal and lateral surfaces of the seals from pelvis to neck.

<p>Points are means, and bars represent ± 1 standard deviation combining distributions of triplicate measures for dorsal surfaces and six measures for lateral surfaces from 13 seals.</p

Measures of circularity.

<p>Width vs. height at different locations along an elephant seal’s body (<i>N</i> = 14 animals, each animal independently measured three times). Points along the diagonal red line indicate circularity.</p

Comparison of truncated cones techniques to estimate blubber volume.

<p>Traditional truncated cones technique (circular cones without ultrasound images, not accounting for skin, blubber from neck to pelvis) vs. a new method (elliptical cones with ultrasound images, accounting for skin, blubber from ears to ankles). Points are means and circles are 95% posterior intervals. Dashed black line is parity. Orange lines are mean (solid) and 95% posterior interval (dashed) values from a hierarchical Bayesian analysis accounting for uncertainty in measurements.</p

Differences between traditional and modified truncated cones methods.

<p>Differences between traditional and modified truncated cones methods.</p