Megan Tierney

A DNA-based method for identification of krill species and its application to analysing the diet of marine vertebrate predators

Accurate identification of species that are consumed by vertebrate predators is necessary for understanding marine food webs. Morphological methods for identifying prey components after consumption often fail to make accurate identifications of invertebrates because prey morphology becomes damaged during capture, ingestion and digestion. Another disadvantage of morphological methods for prey identification is that they often involve sampling procedures that are disruptive for the predator, such as stomach flushing or lethal collection. We have developed a DNA‐based method for identifying species of krill (Crustacea: Malacostraca), an enormously abundant group of invertebrates that are directly consumed by many groups of marine vertebrates. The DNA‐based approach allows identification of krill species present in samples of vertebrate stomach contents, vomit, and, more importantly, faeces. Utilizing samples of faeces from vertebrate predators minimizes the impact of dietary studies on the subject animals. We demonstrate our method first on samples of Adelie penguin (Pygoscelis adeliae) stomach contents, where DNA‐based species identification can be confirmed by prey morphology. We then apply the method to faeces of Adelie penguins and to faeces of the endangered pygmy blue whale (Balaenoptera musculus brevicauda). In each of these cases, krill species consumed by the predators could be identified from their DNA present in faeces or stomach contents.

Energy content of mesopelagic fish from Macquarie Island.

The water and calorific content of fifteen species of mesopelagic sub-Antarctic fish from Macquarie Island were determined. Mean percent water content was 69–82%. Calorific content was highly variable between species, especially in the Myctophidae, where it ranged between 22.6–59.3 kJ·g−1 dry weight. The water and calorific content varied with size class within a species, with the smallest size classes generally having the lowest water content but highest calorific content. These values will be useful for future assessment of energetic transfer between trophic levels and energetic modelling of Southern Ocean ecosystems.

Perfluorinated compounds in the Antarctic region: ocean circulation provides prolonged protection from distant sources

In order to investigate the extent to which Perfluorinated Contaminants (PFCs) have permeated the Southern Ocean food web to date, a range of Antarctic, sub-Antarctic and Antarctic-migratory biota were analysed for key ionic PFCs. Based upon the geographical distribution pattern and ecology of biota with detectable vs. non-detectable PFC burdens, an evaluation of the potential contributory roles of alternative system input pathways is made. Our analytical findings, together with previous reports, reveal only the occasional occurrence of PFCs in migratory biota and vertebrate predators with foraging ranges extending into or north of the Antarctic Circumpolar Current (ACC). Geographical contamination patterns observed correspond most strongly with those expected from delivery via hydrospheric transport as governed by the unique oceanographic features of the Southern Ocean. We suggest that hydrospheric transport will form a slow, but primary, input pathway of PFCs to the Antarctic region.

A comparison of techniques used to estimate body condition of southern elephant seals (Mirounga leonina)

The total body water (TBW) and body condition of 86 female southern elephant seals was estimated from tritiated water (HTO) dilution space analysis. HTO blood samples were analysed using two distillation methods (direct serum counts and evaporative freeze capture) that yielded significantly different estimates. Evaporative freeze capture is recommended for use because it is faster, cheaper, and provides a more precise TBW estimate of dilution space. Estimates of TBW were then compared with those derived from bioelectrical impedance analysis (BIA) and morphometric models. There were significant, positive relationships between TBW and BIA variables, but the level of accuracy was inadequate for BIA to be more useful than the other methods trialled. Morphometric models accurately estimated TBW (kg). Models developed from surface area (SA) (TBW = [SA * 82.58] – 86.94) and from a combination of mass (M), length (L), and girth (G) (TBW = [(M * 0.72) + (L * 5.49) + (G * 134.94) + 164.36)] provided the most accurate TBW estimates. In contrast, condition indices did not give accurate or reliable estimates of relative body condition.

Habitat use and spatial fidelity of male South American sea lions during the nonbreeding period

Abstract Conditions experienced during the nonbreeding period have profound long‐term effects on individual fitness and survival. Therefore, knowledge of habitat use during the nonbreeding period can provide insights into processes that regulate populations. At the Falkland Islands, the habitat use of South American sea lions (Otaria flavescens) during the nonbreeding period is of particular interest because the population is yet to recover from a catastrophic decline between the mid‐1930s and 1965, and nonbreeding movements are poorly understood. Here, we assessed the habitat use of adult male (n = 13) and juvenile male (n = 6) South American sea lions at the Falkland Islands using satellite tags and stable isotope analysis of vibrissae. Male South American sea lions behaved like central place foragers. Foraging trips were restricted to the Patagonian Shelf and were typically short in distance and duration (127 ± 66 km and 4.1 ± 2.0 days, respectively). Individual male foraging trips were also typically characterized by a high degree of foraging site fidelity. However, the isotopic niche of adult males was smaller than juvenile males, which suggested that adult males were more consistent in their use of foraging habitats and prey over time. Our findings differ from male South American sea lions in Chile and Argentina, which undertake extended movements during the nonbreeding period. Hence, throughout their breeding range, male South American sea lions have diverse movement patterns during the nonbreeding period that intuitively reflects differences in the predictability or accessibility of preferred prey. Our findings challenge the long‐standing notion that South American sea lions undertake a winter migration away from the Falkland Islands. Therefore, impediments to South American sea lion population recovery likely originate locally and conservation measures at a national level are likely to be effective in addressing the decline and the failure of the population to recover.