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Climate change will drive fish stocks north – away from where they’re needed most

By the year 2050 it is forecast that the number of people on the planet will have grown to over nine billion: that’s an extra two billion mouths to feed, most of them in developing countries where there already is an unequal distribution of the world’s food.

To help combat this inequality and meet rising demands, many are starting to look to the world’s oceans as a potential source of extra food: currently only five per cent of food production comes from our seas.

But as our demands increase, the question remains whether marine stocks will be able to support present levels of fishing, much less a more intensive fishing regime.

The latest report from the Intergovernmental Panel on Climate Change (IPCC), published last month, painted a less than promising future for marine ecosystems. Changing climate conditions have already reduced species numbers and forced many to shift their geographic ranges, seasonal activities and behaviours.

In the face of all this, the idea that our seas can be relied upon to produce enough food might sound wildly optimistic, but a group of scientists from the Plymouth Marine Laboratories (PML) in the UK believe that the impact of our future climate on fisheries may not be ‘all bad’ for some countries.

In a paper published in Nature Climate Change, Professor Manuel Barange and his colleagues used a unique approach to create what they believe to be one of the best predictors to date of how much our global fishing communities can produce under the changing climate.

Barange’s team wanted to capture the complex physical and biological processes that take place at coastal regions, where the majority of our fish supplies come from. To do this they created an ocean-shelf model which they mapped to 67 national marine ‘exclusive economic zones’: sea zones that one country has exclusive rights to fish in. 

Using this approach they were able to get high-resolution predictions of how particular countries and their coastal fishing areas might fare under changing climate conditions by 2050.

By calculating primary productivity, the total amount of energy that enters the bottom of the marine food web mostly via phytoplankton, the researchers predicted how many fish an ecosystem could potentially support. And rather than getting bogged down in details of whether “haddock will do better than cod”, the model makes estimates of the total fish output in biomass rather than how a specific species might respond.

Their findings have thrown up a somewhat optimistic picture: we can expect a three per cent increase overall in global fish productivity by 2050 with countries at higher latitudes, towards the Polar Regions, seeing the greatest gains.

Fisheries in Norway, Sweden and Iceland are among those most likely to benefit from warming temperatures and expanding habitats for their fisheries. But there were also some surprising beneficiaries at lower latitudes too. Togo, on the Gulf of Guinea, stands to see an increase in fish production potential of almost 24 per cent.

But in contrast to these climate ‘winners’ they expect there to be a general decline in production potential in the tropics where high temperatures already limit primary production, and therefore how many fish an ecosystem can support.

Of greatest concern are countries in South and Southeast Asia, Southwest Africa, Peru, and some tropical, small-island states. The high reliance of populations in these areas on fisheries for food, employment and trade, suggests that the negative impacts may be felt by the people who can afford it least.

“It’s very different for a country that depends on fisheries a lot to be told you might have a 10 per cent decline in production from saying the same message to a country that does not depend on fisheries at all,” says Barange.

“There are winners, and there are losers. This is the most important thing to take away.”

So while the overall outlook might sound favourable for the world’s fish stocks, as the authors themselves write: ‘these assumptions are optimistic, but not utopian’. Their predictions are also dependent on countries putting into practice sustainable harvesting of fish stocks as well as improvements to technologies used by the aquaculture industry.

Dr Beth Fulton, an expert in marine ecosystem modelling at Australia's national science agency, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), believes the study is a good “first go” at looking at how things might turn out for coastal fish stocks but points to some of the limitations in an approach of this kind.

Their outlook for the future is based upon a single global climate model (GCM), and therefore only presents one possible result for our future climate. Fulton believes that using multiple models and multiple scenarios would give a wider range of possible outcomes. Neither does the study take into account some of the other expected negative effects of climate change, such as decreasing oxygen levels and ocean acidification which are likely to make potential gains far from certain, especially at higher latitudes.

And finally, while making some allowances for how trade and populations might change, it does not account for other major social and economic changes that may take place globally over the coming decades.

But in spite of all the uncertainties involved, to look to such studies to give us exact predictions is perhaps missing the point. Rather than definite answers about the state of future fish stocks, “they highlight points to think about as we try to move forward toward the future,” says Fulton.

Barange also acknowledges this uncertainty, saying that it is vital we keep searching for solutions rather than “throw our arms up in the air”. As he points out, governments are already taking these issues seriously: the United Nations are hosting a meeting on ‘The role of seafood in global food security’ next month.

Although the agenda for the meeting is yet to be published, a preliminary report states that world leaders acknowledge that food security and nutrition has become a ‘pressing global challenge’. And that despite the considerable pressures facing our seafood, they see it playing a ‘key’ role in combating both present and future challenges from poverty, hunger and malnutrition.