Jean-Benoit Charrassin

Assessment of scale-dependent foraging behaviour in southern elephant seals incorporating the vertical dimension: a development of the First Passage Time method

1. Identifying the spatial scales at which top marine predators forage is important for understanding oceanic ecosystems. Several methods quantify how individuals concentrate their search effort along a given path. Among these, First-Passage Time (FPT) analysis is particularly useful to identify transitions in movement patterns (e.g. between searching and feeding). This method has mainly been applied to terrestrial animals or flying seabirds that have little or no vertical component to their foraging, so we examined the differences between classic FPT and a modification of this approach using the time spent at the bottom of a dive for characterizing the foraging activity of a diving predator: the southern elephant seal. 2. Satellite relayed data loggers were deployed on 20 individuals during three successive summers at the Kerguelen Islands, providing a total of 72 978 dives from eight juvenile males and nine adult females. 3. Spatial scales identified using the time spent at the bottom of a dive ( = 68.2 +/- 42.1 km) were smaller than those obtained by the classic FPT analysis ( = 104.7 +/- 67.3 km). Moreover, foraging areas identified using the new approach clearly overlapped areas where individuals increased their body condition, indicating that it accurately reflected the foraging activity of the seals. 4. These results suggest that incorporating the vertical dimension into FPT provides a different result to the surface path alone. Close to the Antarctic continent, within the pack-ice, sinuosity of the path could be explained by a high sea-ice concentration (restricting elephant seal movements), and was not necessarily related to foraging activity. 5. Our approach distinguished between actual foraging activity and changes in behaviour induced by the physical environment like sea ice, and could be applied to other diving predators. Inclusion of diving parameters appears to be essential to identify the spatial scale of foraging areas of diving animals.

Estimates of the Southern Ocean general circulation improved by animal‐borne instruments

Over the last decade, several hundred seals have been equipped with conductivity-temperature-depth sensors in the Southern Ocean for both biological and physical oceanographic studies. A calibrated collection of seal-derived hydrographic data is now available, consisting of more than 165,000 profiles. The value of these hydrographic data within the existing Southern Ocean observing system is demonstrated herein by conducting two state estimation experiments, differing only in the use or not of seal data to constrain the system. Including seal-derived data substantially modifies the estimated surface mixed-layer properties and circulation patterns within and south of the Antarctic Circumpolar Current. Agreement with independent satellite observations of sea ice concentration is improved, especially along the East Antarctic shelf. Instrumented animals efficiently reduce a critical observational gap, and their contribution to monitoring polar climate variability will continue to grow as data accuracy and spatial coverage increase.

Comparison of Body Reserve Buildup in Prefasting Chicks and Adults of King Penguins (Aptenodytes patagonicus)

Like other penguin species, adult king penguins (Aptenodytes patagonicus) fast several weeks when they molt and at the beginning of their breeding cycle. Moreover, chicks of this species can withstand up to 5 mo of food deprivation during the austral winter. To assess possible variation in the prefasting amounts of nutrient reserves, we determined body composition (water, protein, total lipid, and ash contents) of adults and chicks of king penguins at the beginning of their long-term fasts. Accumulation of subcutaneous fat stores anticipates each of these periods and appears to be an obligatory prerequisite to fasting However, prewinter chicks contained 1 kg more fat and, consequently, had a higher adiposity (34%) than premolting chicks (22%) and prebreeding adults (18%), indicating that the higher the fat stores, the higher the fast resistance. Prewinter chicks also possess a 19% lower lean body mass (6 61 vs. 8.12 kg in premolting chicks), that is, a low amount of metabolically active tissues, thus minimizing their fasting energy expenditure. When compared with adult breeding fast, adult molt is anticipated by a 3.3-kg body mass increase due mainly to water (67%) and protein (23%). Two tissues (integument and pectoral muscles) account for 84% of this body mass difference. The increase in integument (feather, skin, and subdermal fat) mass involves water and fat (59% and 28% of the mass increase, respectively), whereas that in breast muscle mass involves protein and water (32% and 68% of the increase, respectively). Such protein stores anticipate the use of endogenous body protein for new feather synthesis during the molting fast. This study clearly shows that different amounts of fat and protein are builtup in anticipation of fasts of different durations and nutrient needs in king penguins.

Delayed-Mode Calibration of Hydrographic Data Obtained from Animal-Borne Satellite Relay Data Loggers

A delayed-mode calibration procedure is presented to improve the quality of hydrographic data from CTD‐Satellite Relay Data Loggers (CTD‐SRDL) deployed on elephant seals. This procedure is applied on a dataset obtained with 10 CTD‐SRDLs deployed at Kerguelen Islands in 2007. A comparison of CTD‐ SRDLs with a ship-based CTD system is first presented. A pressure-effect correction, linear with pressure, is deduced for both temperature and salinity measurements. An external field effect on the conductivity sensor is alsodetected, inducinganadditionalsalinityoffset.Thesalinityoffsetcannotbeestimateddirectlyfromthe ship-based CTD comparisons, because the attachment of the CTD‐SRDL on the seal head modifies the magnitudeoftheexternalfieldeffect.Twomethodsareproposedforestimatingaposteriorithesalinityoffset. The first method uses the stable salinity maximum characterizing the Lower Circumpolar Deep Water (LCDW), sampled by seals foraging south of the Southern Antarctic Circumpolar Current Front. Where this approach is not possible, a statistical method of cross-comparison of CTD‐SRDLs surface salinity measurements is used over the sluggish Northern Kerguelen Plateau. Accuracies are respectively estimated as 60.028C for temperature and 60.1 for derived salinity without corrections. The delayed-mode calibration significantly improves the CTD‐SRDL data, improving accuracies to 60.018C and 60.03, respectively. A better salinity accuracy of 60.02 is achieved when the LCDW method can be used. For CTD‐SRDLs where ship-basedCTD comparisons are not available,the expectedaccuracy would be 60.028C for temperatureand 60.04 for the derived salinity.

A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals

The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20–140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate.

Seabirds as monitors of upper-ocean thermal structure. King penguins at the Antarctic polar front, east of Kerguelen sector.

The main objective of this work was to assess the potential of diving birds to monitor the hydrographic features near the Antarctic polar front. We compared the temperature/depth profiles recorded by instrumented King penguins Aptenodytes patagonicus at Kerguelen Islands (South Indian Ocean) with the oceanographic and remote sensing (satellite) data available for the same area during the same season. The birds were equipped with time/depth/temperature recorders or Argos transmitters. In addition, two birds were instrumented (of which one successfully) both with a time/depth/temperature recorder and an Argos transmitter. King penguins foraged as far as 400 km from the coast, in water masses with a vertical temperature structure characteristic of the region just south of the polar front. The temperature/depth profiles recorded throughout the dives (up to 270 m) revealed a pronounced thermocline. A three-dimensional distribution of water temperature was reconstructed. Comparison with previous hydrographic data shows a high correlation. Instrumented predators may therefore usefully and cheaply complement the database provided by conventional hydrographic surveys and remote sensing, especially in distant and rough areas such as the Southern Ocean.

The ocean mixed-layer under Southern Ocean sea-ice: Seasonal cycle and forcing

The oceanic mixed-layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed-layer are poorly understood due to the sparseness of in-situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the Polar Regions. Working with Elephant Seal-derived observations, ship-based and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed-layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary roles.Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed-layer, and impact large-scale water-mass formation and transformation with far reaching consequences for ocean ventilation. This article is protected by copyright. All rights reserved.

Variability in sea ice cover and climate elicit sex specific responses in an Antarctic predator

Contrasting regional changes in Southern Ocean sea ice have occurred over the last 30 years with distinct regional effects on ecosystem structure and function. Quantifying how Antarctic predators respond to such changes provides the context for predicting how climate variability/change will affect these assemblages into the future. Over an 11-year time-series, we examine how inter-annual variability in sea ice concentration and advance affect the foraging behaviour of a top Antarctic predator, the southern elephant seal. Females foraged longer in pack ice in years with greatest sea ice concentration and earliest sea ice advance, while males foraged longer in polynyas in years of lowest sea ice concentration. There was a positive relationship between near-surface meridional wind anomalies and female foraging effort, but not for males. This study reveals the complexities of foraging responses to climate forcing by a poleward migratory predator through varying sea ice property and dynamic anomalies.

The third dimension: a novel set‐up for filming coelacanths in their natural environment

1: Here we describe a novel design to obtain three dimensional data on the movements of aquatic organisms at depths of up to 140 meters. 2: The setup consists of two synchronized high-speed cameras fixed to two articulated arms. 3: The setup was successfully used to film and quantify the locomotion of coelacanths (Latimeria chalumnae) living at a depth of about 120 meters in Sodwana Bay, South Africa. As an example, the detailed motion of the dorsal fin is presented here. 4: This setup can be used for any underwater applications that require synchronized video recordings of medium to large sized animals. This article is protected by copyright. All rights reserved.