Assessing the environmental and ecological drives of interannual variability in the life histories and population dynamics of icefishes (Family Channi

The sub-Antarctic island of South Georgia is a hotspot of regional marine biodiversity in the Southern Ocean and supports high levels of endemic and range-edge fauna. It is also one of the fastest warming areas in the Southern Ocean. This means that many species may find toleration and adaptation to higher temperatures difficult.

In addition, it is an important fishing region in the Southern Ocean. The management of the fisheries is conducted by the Government of South Georgia and the South Sandwich Islands (GSGSSI) under the auspices of CCAMLR. This means GSGSSI are managing fisheries whilst mitigating against longer-term changes in climate.

A key component of the fish fauna around South Georgia are the family Channichthyidae, also known as icefishes. Icefish are unique amongst vertebrates, in lacking the blood pigment haemoglobin, an adaption that may make them particularly susceptible to future warming. Icefish also exhibit unusual reproductive behaviours with some species known to show nesting behaviours.

There are three species of closely related icefish Champsocephalus gunnari (mackeral icefish), Chaenocephalus aceratus and Pseudochaenichthys georgianus, which make up a substantial proportion of the fish biomass on the continental shelves of South Georgia and Shag Rocks and have undergone niche differentiation for successful coexistence. Champsocephalus gunnari is a commercial fisheries target while management measures are in place for the other two species.

However, there are still important gaps in our knowledge of key life history processes, especially related to reproductive cycles and behaviour, and ecological and environmental drives of spatio-temporal variability in biomass and life history stages within these species.

The main objectives of this project are to quantify key life history processes, demographic properties and resource partitioning in the icefishes C. gunnari, C. aceratus and P. georgianus on the South Georgia and Shag Rocks continental shelves. Given the differences in ecological niches for these species, it is expected that they will respond differently to fluctuating environmental conditions.

At present, there are management measures in place which limit the total biomass caught as target or by-catch in the commercial fisheries, but further information is required at the regional scale to help inform the spatial management and maintain viable populations to help mitigate against future warming. Key questions which need to be addressed include:

1) identify potential spawning locations, timings and nursery grounds and assess whether these are linked to environmental or bathymetric features;

2) assess the environmental drivers of interannual variability in recruitment, hatching times and growth rates of larvae; 3) assess the distribution of life history stages around the island and how they vary between and within years; 4) quantify resource partitioning among life history stages of the different species.