Body condition changes at sea: onboard calculation and telemetry of body density in diving animals

This study was supported by grants from the Office of Naval Research N00014-18-1-2822, DoD SERDP contract W912HQ20C0056, IPEV (Institut Paul Emile Victor) under the Antarctic research program 109 (C. Barbraud) and 1201 (C. Gilbert & C. Guinet), and CNES-TOSCA as part of the SNO-MEMO.The ability of marine mammals to accumulate sufficient lipid energy reserves is vital for mammals' survival and successful reproduction. However, long-term monitoring of at-sea changes in body condition, specifically lipid stores, has only been possible in elephant seals performing prolonged drift dives (low-density lipids alter the rates of depth change while drifting). This approach has limited applicability to other species. Using hydrodynamic performance analysis during transit glides, we developed and validated a novel satellite-linked data logger that calculates real-time changes in body density (∝lipid stores). As gliding is ubiquitous amongst divers, the system can assess body condition in a broad array of diving animals. The tag processes high sampling rate depth and three-axis acceleration data to identify 5 s high pitch angle glide segments at depths >100 m. Body density is estimated for each glide using gliding speed and pitch to quantify drag versus buoyancy forces acting on the gliding animal. We used tag data from 24 elephant seals (Mirounga spp.) to validate the onboard calculation of body density relative to drift rate. The new tags relayed body density estimates over 200 days and documented lipid store accumulation during migration with good correspondence between changes in body density and drift rate. Our study provided updated drag coefficient values for gliding (Cd,f = 0.03) and drifting (Cd,s = 0.12) elephant seals, both substantially lower than previous estimates. We also demonstrated post-hoc estimation of the gliding drag coefficient and body density using transmitted data, which is especially useful when drag parameters cannot be estimated with sufficient accuracy before tag deployment. Our method has the potential to advance the field of marine biology by switching the research paradigm from indirectly inferring animal body condition from foraging effort to directly measuring changes in body condition relative to foraging effort, habitat, ecological factors and anthropogenic stressors in the changing oceans. Expanding the method to account for diving air volumes will expand the system's applicability to shallower-diving (<100 m) species, facilitating real-time monitoring of body condition in a broad range of breath-hold divers.Publisher PDFPeer reviewe

Chlorophyll measured by autonomous pinniped oceanographers: Calibration and validation of in situ data collected by northern elephant seals

Increased sampling of the ocean is imperative in today’s rapidly changing climate. In situ chlorophyll fluorescence data collected by northern elephant seals (Mirounga angustirostris) instrumented with oceanographic tags in the northeastern Pacific offer a supplement to other autonomous oceanographic samplers. I carried out a series of cross calibrations to evaluate the quality of these chlorophyll data. I calibrated the fluorometers in Conductivity-Temperature-Depth-Fluorescence tags (CTDF tags, Sea Mammal Research Unit) in the laboratory using extractions of mixed algal cultures representative of the North Pacific and further validated these calibrations in a controlled field setting. CTDF tags were deployed on five adult female northern elephant seals in 2014 at Año Nuevo State Park in California, USA for 2 to 8 month long offshore foraging trips reaching 3,116 to 4,476 km offshore. These deployments yielded 1394 temperature, salinity, and chlorophyll fluorescence casts of at least 180 m depth. The instrumented elephant seals documented subsurface chlorophyll maxima below the first optical depth in 80.7% of casts. Evidence of fluorescence quenching during periods of high irradiance was inconsistent and did not introduce a bias to our results. I compared the in situ chlorophyll data to satellite derived values. Overlapping satellite chlorophyll data were available for 5.9 - 23.5% of the in situ seal-collected data points using matchup criteria ranging from 1 to 8 days and 5 to 10 km. In situ chlorophyll fluorescence readings were higher than overlapping satellite ocean color chlorophyll data by a factor of 1.53 to 4.96. In light of these cross-calibration results, I strongly recommend system specific calibration procedures for fluorometers sampling from autonomous platforms and urge consideration of errors in the sole use of satellite-derived chlorophyll data for ground-truthing This in situ chlorophyll dataset measures an Essential Ocean Variable (EOV) at low cost and can be a valuable resource to the broader scientific community

Chlorophyll measured by autonomous pinniped oceanographers: Calibration and validation of in situ data collected by northern elephant seals

Increased sampling of the ocean is imperative in today’s rapidly changing climate. In situ chlorophyll fluorescence data collected by northern elephant seals (Mirounga angustirostris) instrumented with oceanographic tags in the northeastern Pacific offer a supplement to other autonomous oceanographic samplers. I carried out a series of cross calibrations to evaluate the quality of these chlorophyll data. I calibrated the fluorometers in Conductivity-Temperature-Depth-Fluorescence tags (CTDF tags, Sea Mammal Research Unit) in the laboratory using extractions of mixed algal cultures representative of the North Pacific and further validated these calibrations in a controlled field setting. CTDF tags were deployed on five adult female northern elephant seals in 2014 at Año Nuevo State Park in California, USA for 2 to 8 month long offshore foraging trips reaching 3,116 to 4,476 km offshore. These deployments yielded 1394 temperature, salinity, and chlorophyll fluorescence casts of at least 180 m depth. The instrumented elephant seals documented subsurface chlorophyll maxima below the first optical depth in 80.7% of casts. Evidence of fluorescence quenching during periods of high irradiance was inconsistent and did not introduce a bias to our results. I compared the in situ chlorophyll data to satellite derived values. Overlapping satellite chlorophyll data were available for 5.9 - 23.5% of the in situ seal-collected data points using matchup criteria ranging from 1 to 8 days and 5 to 10 km. In situ chlorophyll fluorescence readings were higher than overlapping satellite ocean color chlorophyll data by a factor of 1.53 to 4.96. In light of these cross-calibration results, I strongly recommend system specific calibration procedures for fluorometers sampling from autonomous platforms and urge consideration of errors in the sole use of satellite-derived chlorophyll data for ground-truthing This in situ chlorophyll dataset measures an Essential Ocean Variable (EOV) at low cost and can be a valuable resource to the broader scientific community

How Oceanography Influences The Foraging Behavior Of A Twilight Zone Predator, The Elephant Seal

In a rapidly changing ocean that remains largely undersampled, physical and biological observations are crucial to understanding, predicting, and mitigating effects of anthropogenic stressors. Animals instrumented with oceanographic sensors offer valuable supplements to datasets from more traditional oceanographic methods while simultaneously offer information about the oceanography of areas significant to the animals. Marine predator foraging behavior relative to physical or biological features such as fronts, eddies, and phytoplankton blooms can be used to infer oceanographic influences on the distribution of pelagic prey. This dissertation applies tracking data from adult female northern elephant seals (Mirounga angustirostris) and southern elephant seals (Mirounga leonina) with in situ temperature, salinity, and chlorophyll fluorescence collected by instruments carried by the seals to investigating relationships between oceanographic features and the foraging behavior of these wide-ranging mesopelagic predators at basin- to submesoscales. Chapter 1 investigated the behavior of northern elephant seals when they encountered eddies. This project used a 17-year dataset of time-depth recorders and concluded that while eddies are a minor feature of their habitat, seals do derive foraging benefits from both cyclonic and anticyclonic eddies. Our observations suggest that physical prey aggregation is a more likely mechanism making eddies beneficial to foraging seals than bottom-up energetic enhancement of the food web resulting from nutrient injection. Chapter 2 combined tracking data from northern and southern elephant seals to compare their behavior relative to the oceanographic conditions they encountered. This first direct comparison between the at-sea behavior of these two closely related species showed comparable movement and diving behavior and further, very similar relationships between behavior and temperature, salinity, and mixed layer depths encountered. Both seal populations were more responsive to horizontal variability in physical conditions during the post-molt trip than during the post-breeding trip and showed these inter-trip differences in behavior despite the seasonal offset in when the trips occur in their relative hemispheres. We conclude that these species employ similar strategies in two contrasting ocean basins, indicating that the mesopelagic prey field may be driven by similar oceanographic properties and seasonal resource pulses in both ocean basins. Chapter 3 used in situ chlorophyll fluorescence data collected by seal-borne instruments and remotely sensed chlorophyll data to test whether elevated chlorophyll concentrations were associated with enhanced foraging behavior in northern elephant seals. We found that real-time chlorophyll data, despite having the advantage of containing subsurface data, did not predict seal foraging behavior. Instead, remotely sensed chlorophyll data from 2-4 months prior to seal presence was associated with elevated foraging behavior. This effect was especially strong during the post-molt season when less of the seals’ range was contained elevated chlorophyll but had several months prior. These chapters illuminate the interplay between intrinsic and extrinsic drivers of behavior and the role of spatiotemporal scale linking physics to biology in the open ocean

Extent and Magnitude of Subsurface Anomalies During the Northeast Pacific Blob as Measured by Animal‐Borne Sensors

Marine heatwaves (MHWs) are prolonged warm water events that are increasing in frequency and magnitude due to rising global temperatures. The Northeast Pacific Blob was an unusually widespread MHW that affected ecosystems across the Northeast Pacific, from producers to top predators. Temperature and salinity data collected by northern elephant seals (Mirounga angustirostris) from 2014 to 2017 show significant (&gt;2 sd) warm anomalies throughout the top 1,000&nbsp;m of the water column, with peak warming in late 2015. Using temperature and salinity as a tracer of layers of constant density, we looked at how lateral advection may have contributed to the development of the Blob. Temperature and salinity anomalies and the expansion of the water column at the base of the pycnocline both indicate that northward advection of warm, salty water played an important role in the observed accumulation of warm water, in addition to surface warming. These findings contribute to our understanding of the physical dynamics of the Blob, especially the thermal content and structure of the water column, and offer mechanisms for its formation and maintenance, which are crucial to assessing the ecological effects of MHWs now and in the future

Sex of depositor and diet proportions for individual scat samples

The file lists the sex of the scat depositor, individual sample ID, sampling month, sampling season, sampling year, and sampling site, as well as the diet proportions of different prey species (in %) for each individual sample used in the study. Salmonid prey species proportions are listed separately for juvenile and adult salmon. The columns with prey species diet proportions are followed by columns showing diet proportions by order (for fish) or higher taxonomic level for invertebrates (Crustacea and Cephalopoda)

Individual variation in life-history timing: synchronous presence, asynchronous events and phenological compensation in a wild mammal.

Many animals and plants have species-typical annual cycles, but individuals vary in their timing of life-history events. Individual variation in fur replacement (moult) timing is poorly understood in mammals due to the challenge of repeated observations and longitudinal sampling. We examined factors that influence variation in moult duration and timing among elephant seals (Mirounga angustirostris). We quantified the onset and progression of fur loss in 1178 individuals. We found that an exceptionally rapid visible moult (7 days, the shortest of any mammals or birds), and a wide range of moult start dates (spanning 6-10× the event duration) facilitated high asynchrony across individuals (only 20% of individuals in the population moulting at the same time). Some of the variation was due to reproductive state, as reproductively mature females that skipped a breeding season moulted a week earlier than reproductive females. Moreover, individual variation in timing and duration within age-sex categories far outweighed (76-80%) variation among age-sex categories. Individuals arriving at the end of the moult season spent 50% less time on the beach, which allowed them to catch up in their annual cycles and reduce population-level variance during breeding. These findings underscore the importance of individual variation in annual cycles

Effects of disease on foraging behaviour and success in an individual free-ranging northern elephant seal

Evaluating consequences of stressors on vital rates in marine mammals is of considerable interest to scientific and regulatory bodies. Many of these species face numerous anthropogenic and environmental disturbances. Despite its importance as a critical form of mortality, little is known about disease progression in air-breathing marine megafauna at sea. We examined the movement, diving, foraging behaviour and physiological state of an adult female northern elephant seal (Mirounga angustirostris) who suffered from an infection while at sea. Comparing her to healthy individuals, we identified abnormal behavioural patterns from high-resolution biologging instruments that are likely indicators of diseased and deteriorating condition. We observed continuous extended (3-30&nbsp;minutes) surface intervals coinciding with almost no foraging attempts (jaw motion) during 2&nbsp;weeks of acute illness early in her post-breeding foraging trip. Elephant seals typically spend ~ 2&nbsp;minutes at the surface. There were less frequent but highly extended (30-200&nbsp;minutes) surface periods across the remainder of the trip. Dive duration declined throughout the trip rather than increasing. This seal returned in the poorest body condition recorded for an adult female elephant seal (18.3% adipose tissue; post-breeding trip average is 30.4%). She was immunocompromised at the end of her foraging trip and has not been seen since that moulting season. The timing and severity of the illness, which began during the end of the energy-intensive lactation fast, forced this animal over a tipping point from which she could not recover. Additional physiological constraints to foraging, including thermoregulation and oxygen consumption, likely exacerbated her already poor condition. These findings improve our understanding of illness in free-ranging air-breathing marine megafauna, demonstrate the vulnerability of individuals at critical points in their life history, highlight the importance of considering individual health when interpreting biologging data and could help differentiate between malnutrition and other causes of at-sea mortality from transmitted data