Seals and killers in the roaring forties with Nico de Bruyn
Channel: Science and Cocktails Johannesburg
Date: 2018-04-30

Science & Cocktails Johannesburg
Date: 27 February 2018
Speaker: Nico de Bruyn (University of Pretoria)

Seals and killers in the roaring forties
Sub-Antarctic Marion Island’s Marine Mammal programme

 How does one keep track of marine mammal populations and why is it important to do so? Can we learn about global population trends by studying a specific ecosystem? And why do we need to go to one of the most remote, inaccessible and inhospitable places on Earth to get this data?

Located halfway between South Africa and Antarctica, Marion island is home to a wide variety of birds as well as marine mammals such as seals and killer whales. Following exploratory research done in the early 1950's, mammal research on Marion Island became a priority scientific endeavour in 1973, leading to the establishment of the Marion Island Marine Mammal Programme in 1983. Precipitous global declines in elephant seal numbers prompted the inception of an intensive mark-recapture programme to better understand the demographics of the elephant seal population on Marion Island in an effort to identify causal mechanisms for the declines there.

Unparalleled data collected over a 30-year timespan has highlighted both juvenile and adult female elephant seal mortality as the immediate drivers of these declines. Although various other hypotheses persist, it has been suggested that the ultimate driver of the population decline is food limitation.

Partly driven by these hypotheses and the evidenced recent stabilisation of the population, the past decade has seen intensive research on other mammalian top-predators within the Marion Island ecosystem, such as killer whales and the role they play in controlling the elephant seal population. This has also stimulated parallel investigations into the basic biology of killer whales, with consequent global implications. Furthermore, studies of otariid (eared) seals on Marion island have helped to disentangle questions pertaining to environmental change, interspecific interactions and important oceanographic features of importance to top-predators from this locality in general.

In this talk, Nico de Bruyn will give us a whirl-wind tour of the research that has driven three decades of scientific inquiry into the population dynamics of mammalian marine top-predators and explain how this research has helped to answer questions of global significance from a region experiencing increased environmental change. 



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