Assessing the environmental and ecological drives of interannual variability in the life histories and population dynamics of icefishes (Family Channichthyidae) around the sub-Antarctic Island of South Georgia.
In the Southern Ocean, there are key knowledge gaps in our understanding of life history processes and how interannual variability influences demographic properties of the endemic fish fauna. A detailed knowledge of life history processes is vital for understanding how different species with differing ecological niches will respond to interannual and longer-term variability in environmental conditions (e.g. temperature, primary productivity). Environmental change can impact marine communities at different spatial and temporal scales. This impact may not be uniform across all species and may lead to different species responding differently to changes in environmental conditions at regional and oceanic scales. Interannual variability in environmental conditions can lead to differences in timing and intensity of spawning, recruitment success and growth rates among marine species. On top of this, large-scale climate oscillations (e.g. ENSO) and oceanic warming can lead to longer term changes in the abundance, distribution and depth range of marine species. The endemic suborder Notothenioidei which dominates the fish fauna on the Southern Ocean continental shelves will potentially be susceptible to regional warming. The notothenioids underwent rapid adaptive radiation after the onset of oceanic cooling in the Southern Ocean which resulted it the seas around Antarctica becoming thermally isolated from connecting oceans. Part of this adaptive radiation is linked to the pelagisation and extending ecological niches into the water column. Understanding the ecological and environmental drivers of interannual and long-term variability in life history and population dynamics of notothenioids is important for conservation and management decisions in the Southern Ocean.
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 gunneri (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 gunneri 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.
The research will feed into GSGSSI’s management of the fisheries and into wider international policies implemented through CCAMLR. A key goal of GSGSSI is to ensure long-term sustainability within their maritime zone by implementing an ecosystem-based approach to management. Fisheries revenue accounts for over 70% of GSGSSI income of which the mackerel icefish fisheries provides an important contribution. These funds help GSGSSI with the environmental management of the islands within their maritime zone and meeting important international obligations for the conservation of higher predators (e.g. birds and whales). The results are expected to contribute towards the developing further enhancement of the GSGSSI’s marine protected areas.