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Climate change: are fishes migrating to colder waters?

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By Milthon Lujan

by Wiida Fourie-Basson, Stellenbosch University 
Are commercially-important fish species adapting to warmer waters in our oceans, or are they moving to cooler areas, thereby becoming locally extinct?

The answer to this important question can have major impacts for the sustainability of local and regional fishing industries, food security and socio-economic stability, especially in areas identified as particularly vulnerable to climate change.

This is why an international team of scientists from South Africa, Portugal, Denmark and Germany have teamed up with stakeholders in their respective regions to identify challenges facing fishing industries under climate change and to collaboratively build bio-economic models, that are climate-resilient and that focus on the sustainability of commercially important marine resources. The project,  titled “GenClim – Biodiversity on the run: evolutionary and socio-economic consequences of shifting distribution ranges in commercially exploited marine fishes”, is funded under the auspices of BiodivERsA – a network funding research on biodiversity, ecosystem services and Nature-based solutions across Europe. In South Africa, the Department of Science and Innovation (DSI) is supporting the research.

On a global scale, research suggests that marine fishes are shifting their distribution ranges towards the poles, or into deeper waters, in order to escape ongoing climate change and warming oceans. Estimates suggest that fishes are shifting their range at a rate of about 31 kilometres per decade, while demersal species shift their distribution by going to deeper waters at a rate of 3.3 meter per decade.

Dr Romina Henriques, an evolutionary biologist from the University of Pretoria and coordinator of the GenGlim project, says there is also evidence of a decrease in body size in some commercially-important fish species, which could be attributed to a combination of climate change and over-fishing.

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Prof Sophie von der Heyden, an evolutionary biologist with a strong focus on marine conservation in SU’s Department of Botany and Zoology and principal investigator on the project, says the South African scenario is quite complex.

“The West Coast is cooling and the East Coast is warming. This means some fishes from the west and south-west coast are extending their range further east. Furthermore, unlike most coastlines in the northern hemisphere, South Africa has a west-to-east rather than a north-to-south coastline. In general the movement of marine species in South Africa in response to climate change are poorly understood, hence this project.”

The project will also cover the North Atlantic, where species from the southern Atlantic are shifting northwards to an extent replacing those species and contributing to novel communities.

Apart from range shifts, climate change is also impacting on population connectivity and the adaptive potential of species, which in turn will affect their distribution patterns and abundance into the future.

Prof von der Heyden explains: “In natural systems, individuals move between different areas and populations. This mechanism ensures gene flow, keeping the populations connected to each other. However, some populations develop a special adaptation to their specific environment. and with climate change, it has become very difficult to predict where species might be in the future and how they will interact with their new environments.”

These effects will spill-over to human societies, given the economic, nutritional and cultural importance of many marine fishes, through shifts in stock sizes and catch composition, Dr Henriques warns.

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“The ability to foresee range shifts and take them into account in fisheries management is essential to anticipate and mitigate potential conflicts in fisheries, secure livelihoods and fulfil international obligations and ultimately preserve marine biodiversity,” she says.

According to Prof von der Heyden, the project has a strong focus on stakeholder engagement across academia, government and industry from the initial project planning stages, to its conclusion: “This is to ensure that science can properly address the questions of multiple stakeholders, so that solutions will find immediate uptake in the hands of policy- and decision makers.”

The GenClim project brings together state-of-the-art genomics, forecasting modelling and socio-economic modelling to disentangle the multiple consequences of range shifts of the demersal hakes (Merluccius merluccius and M. paradoxus) and pelagic anchovy (Engraulis encrasicolus).

The main partners are the Department of Botany and Zoology at Stellenbosch University in South Africa, the Centre for Ocean and Society at the University of Kiel in Germany, the Centre for Marine Sciences (CCMAR) and the University Institute of Psychological, Social and Life Sciences, both in Portugal, and the National Institute of Aquatic Resources at the Technical University of Denmark (DTU).

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