The take of fish species by seabirds and marine mammals in the Australian Fisheries Zone around Heard Island: the potential for competition with a commercial fishery

The number of predators from Heard Island foraging in shelf waters, their prey requirements, and the proportion of their diet that was commercial and non-commercial fish were estimated. The calculated annual consumption of commercial fish species varied between 36,360 and 84,166 tonnes. The non-commercial Krefftichthys anderssoni was the preferred prey for most predators, and when its occurrence in diets was low it was replaced by crustaceans and commercial fish species. The estimated annual consumption of Champsocephalus gunnari was approximately 2 and 6 times the highest and lowest estimates respectively of the biomass of this species, obtained from three fisheries research cruises. For Dissostichus eleginoides, the maximum estimate was 28% of the highest estimate of biomass. The current fishery for D. eleginoides will most likely impact on southern elephant seals, whose population decreased by 50% between the 1950s and the 1980s, possibly as a result of overfishing around Iles Kerguelen

Calibrating the time span of longitudinal biomarkers in vertebrate tissues when fine-scale growth records are unavailable

Biological markers (biomarkers) are invaluable and widely adopted in ecology, archaeology, and anthropology. Serially sampling biomarkers along continuously growing inert tissue, such as vibrissae, hair, nail, horn, or baleen, is an ideal method by which to capture the changes in an individual's diet, environment, climate, health, and stress levels. However, there are complications in calibrating the time periods that samples represent. Here, we assess how the choice of model and the input data used affect the prediction of time span. We use the Antarctic leopard seal, Hydrurga leptonyx, as our model, with stable isotope data from the vibrissae of captive and wild animals. We show that for tissues with nonlinear growth, and where fine-scale data on tissue growth are unavailable, modeling over the life span of the tissue is a simple and easily adopted approach. In this method, growth parameters are derived from surveys of the study population and the shed.replacement cycle to calibrate the time span of the biomarker data. This model performed better than linear and nonlinear models, which use parameters that have been derived from growth measurements documented over short periods relative to the life span of the tissue. These latter approaches performed in a similar fashion to each other as they tended to overestimate the life span of the tissue. Whether growth is linear or nonlinear, not accounting for position-specific differences in growth (rates or coefficients) and asymptotic length (L∞) resulted in different interpretations of biomarker data across the samples collected from the same individual. In species where metabolically inert tissue grows in a progressive fashion, the ability to account for time-specific information refines our ability to interpret the biomarker data. We recommend that this approach be adapted for tissue, such as the vibrissae and hair of mammals and the hair of humans, which exhibit the predictable growth

Changes in isotopic signatures suggest food web shift off the western Antarctic Peninsula

The local warming occurring within the western Antarctic Peninsula (WAP) is causing some of the greatest environmental shifts on the planet.  Over the past 140 years there have been profound biological and physical perturbations to the wildlife on the WAP. We examined whether trophic level shifts were evident in the top predators within this system and use stable isotope signatures as a proxy. Contemporary WAP leopard seals have different nitrogen isotopic values to other leopard seal populations, however historically WAP leopard seals had δ15N values within the range of other western and eastern Antarctic populations. From our 140 yr record of leopard seal tissues (n = 167), we show that the δ15N values of WAP leopard seal tissues have dropped significantly, and that this change occurs as a step around the 1980s. The magnitude (2.6o/oo δ15N) of change is ecologically significant as it reflects a drop of a trophic level within the contemporary WAP food web. Values suggest that leopard seals have shifted from eating vertebrates to krill. Over this same time period there was no shift in δ15N of the WAP krill-feeding specialist, the crabeater seal, which supports the idea that the change in leopard seal δ15N values is not due to a baseline shift in the nitrogen isotope values. Despite the century-long perturbation in the WAP, the top-predators, the seals, show a trophic downshift only in recent times, post 1980s

Environmental predictive models for shark attacks in Australian waters

Shark attacks are rare but traumatic events that generate social and economic costs and often lead to calls for enhanced attack mitigation strategies that are detrimental to sharks and other wildlife. Improved understanding of the influence of environmental conditions on shark attack risk may help to inform shark management strategies. Here, we developed predictive models for the risk of attack by white Carcharodon carcharias, tiger Galeocerdo cuvier, and bull/ whaler Carcharhinus spp. sharks in Australian waters based on location, sea surface temperature (SST), rainfall, and distance to river mouth. A generalised additive model analysis was performed using shark attack data and randomly generated pseudo-absence non-attack data. White shark attack risk was significantly higher in warmer SSTs, increased closer to a river mouth