Warming seas and vanishing fish
1 October 2012
Scientific study predicts fall in stocks and reduction in size of fish as a result of climate change
Climate change threatens to wipe out food source for billions
Fish to shrink by up to a quarter due to climate change, study reveals
Scientists predict 14-24% reduction in fish size by 2050 as ocean temperatures increase
https://www.theguardian.com/environment/2012/sep/30/fish-shrink-climate-change
Research led by Prof William Cheung, from the University of British Columbia in Canada, predicts a reduction in the size of fish by as much as a quarter as a result of global warming. The research also predicts a reduction in overall fish stocks, a perilous situation at a time when a growing human population will place fisheries under ever increasing pressure.
"We were surprised, as we did not think the effects would be so strong and so widespread," comments Prof. Cheung, whose work is published in Nature Climate Change.
Examining the effect of rising ocean temperatures on the growth and distribution of more than 600 species of fish around the world, Cheung and his team found that individual fish are likely to shrink in size by as much as 14-24% by 2050, particularly in tropical regions. Whilst Prof Callum Roberts, at the University of York, described the research as the most comprehensive to date, he claims that "it could be worse than that." Roberts, who was not part of the research team, points out that additional impacts of climate change such as the acidification of the oceans and reduction of nutrients in surface waters, along with continued overfishing, would serve to decrease fish stocks even further.
My old economics teacher once asked me at the start of a lesson, ‘how productive is the sea?’ Apparently there was a lead article in The Economist asking precisely this question. The article was about oil. Not knowing what to say, I stalled for time and asked whether he meant in terms of the natural contents of the seas or the money that could be made out of them. My knowledge of economics may have been poor, but my ecological instincts were good. How productive is the economy in comparison with the ecology of the planet? Where does real value lie? In ecological terms, the sea is very productive.
Coral reef in Ras Muhammad nature park (Iolanda reef)
"We will see dramatic changes in the oceans likely to reduce productivity”, argues Roberts. “One billion people rely on fish for primary animal protein and that is going to increase, especially in developing countries. We have to get to grips with our dependence on fossil fuels, otherwise we are stuffed."
The shrinkage in the size of fish predicted by the Cheung study results from two effects: the difficulty of growing in warmer, oxygen-poor waters, and migration. "The metabolic rate of fish in the warm oceans increases and therefore they need more oxygen," said Cheung. However, since warm water holds less oxygen, fish growth is limited. Further, the more small-bodied fish in the tropics will migrate to temperate or polar regions as the ocean warms, thus reducing the average fish size. Referring to a 2011 study that showed the correlation of the reduction in the size of haddock in the North Sea with increasing temperature, Cheung argues that "we are already seeing the effects."
For Cheung, the conclusions are clear. "Our work shows a very concerning future for the oceans and so it is very important to reduce greenhouse gas emissions and develop better fish management policies to adapt to these changes."
Again, science has done its best. Problems have been explained and solutions identified. It is over to politics, governments and the people now.
For Prof. Roberts, the research indicates that the impact of climate change on the oceans is likely to be greater than had been previously thought. We already knew of the reduction in the size of fish as a consequence of overfishing, fish increasingly living fast and dying young, before they could reach full size. But, Roberts adds, if this overfishing continues, the effect would add to the shrinkage caused by global warming.
Moreover, increasing levels of carbon dioxide in the atmosphere would result in more of the gas dissolving in the ocean, thus accelerating acidification. "That makes life much tougher for animals that make a chalky skeleton," adds Roberts. "We need to worry about these tiny animals … which are an important part of primary production: the base of the food chain."
Roberts continues by pointing out that the heating of the oceans means that the warmer layer at the surface comes to mix less with the colder layer below. Since the colder layer contains most of the nutrients, there will be less food for fish. "We are already seeing some evidence of this, as oceanic 'deserts' are getting larger," concludes Roberts.
Roberts’ final message is simple, direct and clear. "All this is yet one more reason to do something to cut greenhouse gases urgently." It is a message that politicians, journalists and the general public have difficulty understanding. For all of its clarity, it could be written in Egyptian hieroglyphics as far as some people are concerned.