Seminars

The aim of this seminar is to give an overview of the ongoing research that is being conducted by St Andrews as part of the Antarctic Circumnavigation Expedition (ACE, https://spi-ace-expedition.ch/). From December 2016 to March 2017, scientific teams from all over the world took part in this expedition to expand our understanding of the Southern Ocean (from biology to climatology to oceanography). Our project on ACE was to study the acoustic prey landscape of Antarctic deep-diving predators (King Penguins and Southern Elephant Seals). Mesopelagic fish (e.g. myctophids), zooplankton and other organisms migrate down to the mesopelagic zone (200-1000m) to avoid visual predators during the day. There, they form layer-like aggregations known as Deep Scattering Layers (DSLs), which can be detected by echosounders. Myctophids are potential resources for fisheries but are also important in the diets of Antarctic predators such as King Penguins and Elephant Seals. During the ACE expedition, we investigated the interaction between myctophids and these predators by monitoring simultaneously DSL characteristics and predator foraging behaviour. We compiled a dataset of geographic variability in DSL depth and echo-intensity throughout the Southern Ocean. Concomitantly, we collected track data, dive profiles and accelerometry data from King Penguins breeding at South Georgia, and tack and dive data from Elephant Seals. We found that DSL echo-intensity (a proxy of biomass) can be predicted well from sea surface temperature, and that sun angle plays a major role in DSL depth. Habitat modelling techniques revealed that King Penguins preferentially selected habitats based on DSL availability. They targeted zones characterised by dense and shallow DSLs. However, a more detailed analysis of diving activity showed that the penguins’ dive depths were generally shallower than the DSL depth, indicating that they might not feed on the layers themselves, but instead target prey patches above the DSLs. For Elephant Seals (work ongoing) there are some good alignments between dive depths and DSL depths. One objective of our work aims to improve understanding of predator-prey interactions to inform conservation management before any large-scale fisheries exploitation of mesopelagic fish begins.