Vibrissal growth parameters of southern elephant seals Mirounga leonina : obtaining fine-scale, time-based stable isotope data

Stable isotopes provide a powerful, indirect approach to assess the trophic ecology of individuals on a spatial and temporally integrated basis (especially when combined with telemetry). However, using stable isotopes requires accurate, species-specific quantification of the period of biomolecule deposition in the sampled tissue. Sequentially sampled vibrissae (whiskers) provide a chronology of biogeochemical data, although knowledge of the vibrissal growth is required for temporal interpretations. We sampled vibrissae from southern elephant seals (Mirounga leonina, hereafter SES) at Marion Island, southern Indian Ocean to address the following aims: define the prevalence and timing of their vibrissal replacement; determine the vibrissal regrowth rate and temporal resolution of isotopic data captured along the length of sequentially sampled vibrissae; and explore assumptions regarding their vibrissal growth. Contrary to the previously described asynchronous vibrissal shedding pattern of SES, 71.1 % of individuals displayed vibrissal shedding during the annual pelage moult. Furthermore, vibrissa growth ceased once the asymptotic length was reached, and the vibrissae were retained before being replaced. Vibrissae with known growth histories were re-sampled at multiple, known intervals to control for unknown growth starting dates. Vibrissae followed a von Bertalanffy growth function [ ( )( ) ], as the growth rate decreased near the asymptotic length. The resolution of the isotopic data obtainable per 2 mm section ranged from 3.5 days at the vibrissal tip to > 40 days at the base. Using these defined growth rates and shedding patterns, researchers can prudently apply timestamps to stable isotope values along vibrissae.The South African Department of Science and Technology, through the National Research Foundation (NRF), within the South African National Antarctic Programme (SANAP).http://www.int-res.com/journals/meps/meps-home2017-11-30hb2016Mammal Research InstituteZoology and Entomolog

Can the carbon and nitrogen isotope values of offspring be used as a proxy for their mother’s diet? Using foetal physiology to interpret bulk tissue and amino acid δ15N values

Please read abstract in the article.Data will be made available on the Dryad Digital Repository.The Society for Marine Mammalogy (SMM) Small Grant in Aid of Research, the National Research Foundation (NRF), with the logistic support of the Department of Environmental Affairs under the South African National Antarctic Program (SANAP).https://academic.oup.com/conphyshj2020ImmunologyMammal Research InstituteZoology and Entomolog

Fasting affects amino acid nitrogen isotope values: a new tool for identifying nitrogen balance of free-ranging mammals

Changes in the nutritional status of free-ranging animals have a strong influence on individual fitness, yet it remains challenging to monitor longitudinally. Nitrogen (δ15N) and carbon (δ13C) isotope values measured chronologically along the length of metabolically inert keratinous tissues can be used as a nutritional biomarker to retrospectively reconstruct the foraging ecology and eco-physiology of consumers. We quantitatively describe the physiological effects of fasting on amino acid metabolism using sequentially measured bulk tissue and amino acid δ15N values along the length of whiskers sampled from free-ranging juvenile, subadults, adult female, and male southern elephant seals (SES; Mirounga leonina) on Marion Island in the Southern Ocean. For both juveniles and adult females, whisker segments representing fasting had significantly higher bulk tissue δ15N values of 0.6 ± 0.5‰ and 1.3–1.8‰, respectively, in comparison to segments unaffected by fasting. We also found a large increase (2–6‰) in δ15N values for most glucogenic amino acids and a simultaneous depletion (2–3‰) of alanine in segments reflecting fasting, which enabled us to accurately predict (74%) the nutritional status of our model species. We hypothesize that the glucose-alanine cycle is the mechanism driving the observed depletion of alanine δ15N values during fasting. We demonstrated that keratinaceous tissues can be used as a longitudinal nutritional biomarker to detect changes in the nitrogen balance of an individual. Moreover, it is evident that physiological factors have an important influence on tissue δ15N values and can lead to erroneous bulk tissue or amino acid isotope-based reconstructions of foraging habits.The National Research Foundation (NRF) and the ‘Society for Marine Mammalogy (SMM) Small Grant in Aid of Research’.http://link.springer.com/journal/4422021-04-16hj2020ImmunologyMammal Research InstituteZoology and Entomolog

Trophic ecology and persistence of invasive silver carp Hypophthalmichthys molitrix in an oligotrophic South African impoundment

The alien invasive silver carp Hypophthalmichthys molitrix established a self-sustaining feral population in an oligotrophic impoundment, Flag Boshielo Dam, in South Africa. The ability of this population to persist in a dam with low algal biomass (median annual suspended chlorophyll a = 0.08 µg l−1), and limited access to rivers considered large enough for successful spawning, has implications for their invasive potential in other systems. Stomach content and stable isotope analysis were used to assess the trophic ecology of H. molitrix, which was then compared with indigenous Mozambique tilapia Oreochromis mossambicus, on a seasonal basis during 2011. Hypophthalmichthys molitrix are generalist filter feeders, with a diet consisting primarily of sediment, vegetative detritus, dinoflagellates and diatoms. The dominance of sediments in their stomachs suggests occasional benthic scavenging. However, H. molitrix occupied a higher trophic level (TL = 2.8) than expected, suggesting that this population subsidised their diet with an unidentified dietary constituent, characterised by enriched nitrogen values. Although the stomach contents indicated dietary overlap between H. molitrix and O. mossambicus, stable isotopes revealed fine-scale resource partitioning, despite both species occupying the same trophic level. Nonetheless, the persistence of this feral H. molitrix population in an oligotrophic impoundment highlights their phenotypic plasticity.The Olifants River Forum, the DST-NRF Centre of Invasion Biology, University of Pretoria and the National Research Foundation (NRF).http://www.tandfonline.com/loi/taas202017-12-31hb2016Zoology and Entomolog

Antarctic pack ice seal observations during spring across the Lazarev Sea

The distribution, density and percentage contribution of pack ice seals during ship-board censuses in the marginal sea ice zone beyond the Lazarev Sea in spring 2019 are presented. Adult/juvenile crabeater seals (n = 19), leopard seals (n = 3) and Ross seals (n = 10) were sighted during 582.2 nm of censuses along the ship’s track line in the area bounded by 00°00’–22°E and 56°–60°S. Antarctic fur seals (n = 21) were only encountered on the outer fringes of the pack ice, and Weddell seals were absent due to their primary use of fast ice and inner pack ice habitats close to the coast. Crabeater seal sightings included juveniles (n = 2) and another four groups of 2–3 unclassified crabeater seals, singletons (n = 5), single mothers with pups (n = 3) and a family group (n = 1 triad). Only one leopard seal attended a pup, while no Ross seal pups were located. The survey was likely of insufficient effort, in both extent (north of 60°S) and duration (18 days), to locate seals in considerable numbers this early (late October/early November) in their austral spring breeding season.The National Research Foundation (NRF)http://www.cambridge.org/polhj2022Mammal Research InstituteZoology and Entomolog

Opportunistic ship-based census of pack ice seals in eastern Weddell Sea, Antarctica

The distribution, density and percentage contribution of pack ice pinnipeds during ship-board censuses in the eastern Weddell Sea in summer 2015/2016 are presented. Of the four true pack ice seal species encountered, crabeater seals predominated. Despite the low survey effort, Ross seals continued to be relatively abundant in the pack ice off the Princess Martha Coast in mid-January 2016, similar to the situation here in the 1970s. Censusing of Ross seals is ideally carried out in late January/early February when the species’ haulout probability is at its maximum and the seals are gathered in the limited summer pack ice to moult.The Department of Science and Technology (DST), through the National Research Foundation (NRF) (Grant Number 93088).http://link.springer.com/journal/3002020-01-01hj2018Mammal Research InstituteZoology and Entomolog

Habitat use and diet of the Ross seal in the eastern Weddell Sea

The Ross seal (Ommatophoca rossii) is the least studied of the Antarctic pack-ice pinnipeds. Currently only two publications on the at-sea movements (n = 14 individuals) and three publications on their diving behaviour (n = 16 individuals) exist. Furthermore, only one of these publications studied animals from the Weddell Sea (Blix & Nordoy 2007). Unlike the other ice-breeding seals (i.e. Weddell, Leopard, and Crabeater seals), Ross seals are known to forage pelagically most of the year. We deployed satellite-linked tracking devices in the eastern Weddell Sea on 13 Ross seals (n = 11 in 2016; n = 2 in 2018), of which 6 of these devices also recorded diving behaviour. We combined this data with already published satellite telemetry and diving data from ten individuals tracked during 2001 (Blix & Nordoy 2007). For each individual’s track, we simulated a set of pseudo-tracks that allowed a presence-availability habitat modelling approach, which estimates an animal’s habitat preference. We modelled these tracks as a response to several remotely sensed environmental variables by means of ensemble models of boosted regression trees and random forests. Preliminary results suggest that Ross seals forage at the southern boundary of the Polar Front and avoid areas of high eddy activity. During the winter months, some individuals will forage at the edge of the sea-ice, while others remain to forage within the vicinity of Bouvetøya. Most individuals traversed the Southern Ocean 2-3 times during a single year, before returning to Antarctica in January for their annual moult. Ross seals dived on average to 100-300 m deep with a deepest dive of 792 m recorded. Ross seals present a unique opportunity to sample the water masses close to the Antarctic pack-ice edge and do cross-sections of the Southern Ocean year round – especially during winter when ships and other autonomous sampling platforms cannot enter the ice

What’s in a whisker? High-throughput analysis of twenty-eight C19 and C21 steroids in mammalian whiskers by ultra-performance convergence chromatography-tandem mass spectrometry

Obtaining longitudinal endocrinological data from free-ranging animals remains challenging. Steroid hormones can be extracted sequentially from non-invasively sampled biologically inert keratinous tissues, such as feathers, nails, hair and whiskers. However, uncertainty regarding the type and levels of steroids incorporated into such tissues complicates their utility in wildlife studies. Here, we developed a novel, comprehensive method to analyze fourteen C19 and fourteen C21 steroids deposited chronologically along the length of seal whiskers in a single, 6-minute chromatographic step, using ultra-performance convergence chromatography-tandem mass spectrometry. The limits of detection and quantification ranged from 0.01 to 2 ng/mL and from 0.1 to 10 ng/mL, respectively. The accuracy and precision were within acceptable limits for steroids at concentrations ≥2 ng/mL. The recovery (mean = 107.5% at 200 ng/mL), matrix effect and process efficiency of steroids evaluated, using blanked whisker matrix samples, were acceptable. The method was applied to the analysis of steroid hormone levels in adult female whisker segments obtained from southern elephant seals (Mirounga leonina), n = 10, and two fur seal species, Antarctic fur seals (Arctocephalus gazella; n = 5) and subantarctic fur seals (Arctocephalus tropicalis; n = 5), sampled between 2012 and 2017. In the whisker subsamples analyzed (n = 71), the median concentration of steroid hormones detected above the LOQ ranged from 2.0 to 273.7 pg/mg. This was the first extraction of multiple C19 and C21 steroids, including their C11-oxy metabolites, from the whiskers of mammals. Measuring hormones sequentially along the whisker lengths can contribute to our understanding of the impact of stress associated with environmental/climate changes that affect the health, survival of organisms, as well as to delineate the reproductive cycles of free-living mammals with cryptic life stages.http://www.elsevier.com/locate/chromb2021-03-15hj2020ImmunologyMammal Research InstituteZoology and Entomolog

Low trophic level diet of juvenile southern elephant seals Mirounga leonina from Marion Island : a stable isotope investigation using vibrissal regrowths

Insight into the trophic ecology of marine predators is vital for understanding their ecosystem role and predicting their responses to environmental change. Juvenile southern elephant seals (SES) Mirounga leonina are considered generalist predators within the Southern Ocean. Although mesopelagic fish and squid dominate their stomach lavage samples, the stable isotope profile captured along the length of sampled vibrissae of young SES at Macquarie Island, southwest Pacific Ocean (54.5° S, 158.9° E) recently emphasized the contribution of crustaceans to their diet (likely Euphausia superba). Herein, we used the stable isotope values of sampled vibrissal regrowths with known growth histories to assess the diet of juvenile SES at Marion Island, southern Indian Ocean (46.8° S, 37.8° E) on a temporally integrated basis. We specifically aimed to quantify the possible contribution of crustaceans to the diet of juvenile SES. Sequentially (chronologically) sampled vibrissal regrowths of 14 juvenile SES produced fine-scale dietary information spanning up to 9 mo. The depleted stable isotope signatures of nitrogen (δ15N) (8.5 ± 0.6‰) and carbon (δ13C) (−20.3 ± 0.1‰) measured during the period of independent foraging suggested the use of a lower trophic level diet within the Polar Frontal Zone. A mixing model predicted that up to 76% of juvenile SES diet comprised crustaceans, consisting of 2 crustacean groups, each contributing 26% (credible interval, CI: 13−39%) and 50% (CI: 35−64%) to their diets, presumably representing subantarctic krill species. This first utilisation of the isotopic signature captured along the length of vibrissal regrowths confirms the inclusion and importance of crustaceans in the diet of juvenile SES.The South African Department of Science and Technology (DST) and National Research Foundation (NRF), grant number 93071.http://www.int-res.com/journals/meps/meps-home2018-08-30hj2017Jurisprudenc