Trophic position and foraging ecology of Ross, Weddell, and crabeater seals revealed by compound-specific isotope analysis

Ross seals Ommatophoca rossii are one of the least studied marine mammals, with little known about their foraging ecology. Research to date using bulk stable isotope analysis suggests that Ross seals have a trophic position intermediate between that of Weddell Leptonychotes weddellii and crabeater Lobodon carcinophaga seals. However, consumer bulk stable isotope values not only reflect trophic dynamics, but also variations in baseline isotope values, which can be substantial. We used compound-specific isotope analysis of amino acids (CSI-AA) to separate isotopic effects of a shifting baseline versus trophic structure on the foraging ecology of these ecologically important Antarctic pinnipeds. We found that Ross seals forage in an open ocean food web, while crabeater and Weddell seals forage within similar food webs closer to shore. However, isotopic evidence suggests that crabeater seals are likely following sea ice, while Weddell seals target productive areas of the continental shelf of West Antarctica. Our CSI-AA data indicate that Ross seals have a high trophic position equivalent to that of Weddell seals, contrary to prior conclusions from nitrogen isotope results on bulk tissues. CSI-AA indicates that crabeater seals are at a trophic position lower than that of Ross and Weddell seals, consistent with a krill-dominated diet. Our results redefine the view of the trophic dynamics and foraging ecology of the Ross seal, and also highlight the importance of quantifying baseline isotope variations in foraging studies

Reproduktionsperioder och andra störningskänsliga perioder hos säl : En kunskapssammanställning omgråsäl, knubbsäl och vikaresäl

På uppdrag av Naturvårdsverket har författarna sammanställt befintliga fakta om de tre i Sverige förekommande sälarternas biologi med avseende på årstid och störningskänslighet. De har även summerat de sista årens faktiska säljakt och hur den är distribuerad över året.  De tre sälarterna, gråsäl, knubbsäl och vikare har olika ekologi och årscykel, men lika för alla är att sälarnas mest störningskänsliga period är då honorna samlas för att föda sina kutar och de efterföljande veckorna av digivning. Under denna period är de beroende av land eller is för att dia sina ungar och låta ungarna vila. Den näst mest känsliga perioden är under pälsbytet. Då går sälarnas meta­bolism upp till det dubbla och de är även under denna tid beroende av land för att gynna ökad blodtillförsel i den varma torra huden vilket underlättar den nya pälsens tillväxt. Störningar som skrämmer hela kolonin i vattnet (både vid jakt och båtturism) under pälsbytestiden kommer att stressa sälarnas energibudget. Författarna rekommenderar framtida studier av sälarnas beteenden, särskilt vad gäller hur mycket tid de tillbringar på land under olika årstider och i olika delar av utbredningsområdet. De uppgifter som har sammanställts kommer från äldre studier under förhållanden då både sälbestånden var mindre och klimatet kallare. Modern inventeringsmetodik tillåter också en högre grad av upplösning i resulta­ten och kommer ge ett bättre underlag för adaptiv förvaltning. Författarna har för varje art pekat på specifika kunskapsluckor vad gäller säsongsmässigt beteende och störningskänsliga perioder

Life cycle bioenergetics of the gray seal (Halichoerus grypus) in the Baltic Sea: Population response to environmental stress

Wildlife population dynamics are shaped by multiple natural and anthropogenic factors, including predation, competition, stressful life history events, and external environmental stressors such as diseases and pollution. Marine mammals such as gray seals rely on extensive blubber layers for insulation and energy storage, making this tissue critical for survival and reproduction. This lipid rich blubber layer also accumulates hazardous fat soluble pollutants, such as polychlorinated biphenyls (PCBs), that can directly impact adipose function or be mobilized during periods of negative energy balance or transferred to offspring to exert further impacts on target tissues or vulnerable life stages. To predict how marine mammals will respond to ecological and anthropogenic stressors, it is necessary to use process-based modelling approaches that integrate environmental inputs, full species life history, and stressor impacts with individual dynamics of energy intake, storage, and utilization. The purpose of this study was to develop a full lifecycle dynamic energy budget and individual based model (DEB-IBM) that captured Baltic gray seal physiology and life history, and showcase potential applications of the model to predict population responses to select stressors known to threaten gray seals and other marine mammals around the world. We explore variations of three ecologically important stressors using phenomenological simulations: food limitation, endocrine disrupting chemicals that reduce fertility, and infectious disease. Using our calibrated DEB-IBM for Baltic gray seals, we found that continuous incremental food limitation can be more detrimental to population size than short random events of starvation, and further, that the effect of endocrine disruptors on population growth and structure is delayed due to bioaccumulation, and that communicable diseases significantly decrease population growth even when spillover events are relatively less frequent. One important finding is the delayed effect on population growth rate from some stressors, several years after the exposure period, resulting from a decline in somatic growth, increased age at maturation and decreased fecundity. Such delayed responses are ignored in current models of population viability and can be important in the correct assessment of population extinction risks. The model presented here provides a test bed on which effects of new hazardous substances and different scenarios of future environmental change affecting food availability and/or seal energetic demands can be investigated. Thus, the framework provides a tool for better understanding how diverse environmental stressors affect marine mammal populations and can be used to guide scientifically based management.EU-projekt BONU

An assessment of Dinophysis blooms in the coastal Arabian Sea

Dinoflagellate blooms of the genus Dinophysis occur regularly in the coastal Arabian Sea. By producing toxins, which may accumulate in marine bivalves, they impose threat to human health. Using time-series data on environmental variables (e.g., nutrients, sea surface temperature and salinity) and concurrent Dinophysis abundances for the surface waters along the coast of the southeastern Arabian Sea during the period 1990–2010, we investigate whether potential climate change signals play a role in driving blooms of Dinophysis spp. A logistic Generalized Linear Model was adopted to test the effect of environmental variables on Dinophysis abundances over a range of threshold values (102–105 cells m−3) for blooms. Some of the extreme events occurred during the pre-monsoon (March–May) periods. Model validation suggested a threshold of 105 cells m−3 to be better than other thresholds in examining the Dinophysis abundances, and the variation in this threshold is explained by sea surface temperature, salinity, dissolved inorganic nitrogen to phosphorus ratio and total suspended solids (turbidity). Fate of the Dinophysis blooms in the coastal Arabian Sea for different climate change scenarios is discussed