Fish are expected to be up to a quarter smaller by 2050 than they are currently as a result of global warming and the expected changes to the marine ecosystem from climate change, according to research published online in the journal Nature Climate Change September 30.
The scientists argue that failure to control greenhouse gas emissions will have a greater impact on marine ecosystems than previously thought.
Fisheries scientists at the University of British Columbia have used computer modeling to study the effect of climate change on over 600 species of fish from oceans all around the world, using data from one of the higher emissions scenarios developed by the Intergovernmental Panel on Climate Change or IPCC.
Although the changes to actual ocean temperatures that the study projected will be quite small, statistically speaking, the effects on the body size of the fish are "unexpectedly large" according to the published results. Rising ocean temperatures will result in an increase in the body temperature of the fish who live in them. This rise in temperature will result in an increase in the metabolic rate of the fish.
A warmer ocean will be a less oxygenated one and the resultant oxygen starvation is likely to cause a significant decline in the size of fish. The scientists have found that the maximum body weight that the fish may achieve could decline by between 14 and 20 percent by 2050 from 2000 levels. Fish in the tropics will be most significantly affected.
According to materials provided by the University of British Columbia, this is the first global-scale application of the idea that fish growth is limited by oxygen supply, which was pioneered more than 30 years ago by Daniel Pauly, principal investigator with UBC's Sea Around Us Project and the study's co-author.
Previous studies have indicated that changing ocean temperatures are likely to affect both the distribution of fish species as well as their reproductive abilities, however, this is the first research to show that an additional impact will be to size as well.
This study highlights the need to curb greenhouse gas emissions and develop strategies to monitor and adapt to changes that we are already seeing, or we risk disruption of fisheries, food security and the way ocean ecosystems work.
The computer modeling performed by the scientists also predicted that fish populations will move more towards the Earth's poles by research team also used its model to predict fish movements as a result of warming waters. The group believes that most fish populations will move towards the Earth's poles by as much as 36 kilometres or around 22 and a half miles per decade.
When both the population movement and the physiological impacts to metabolism of the rising ocean temperatures are taken into account, the scientists concluded that the likely decrease in fish body size will be in the order of between 14 and 24 percent, with the inhabitants of the Indian and Atlantic Oceans being worst affected.
The results of this fairly conservative study, which when compared with actual observations of fish sizes may actually be underestimating the real effect, suggest that fisheries yields are likely to be significantly reduced in the near future, in terms of both number and size of fish.
As always, further research is required before a definitive answer can be provided, however, this study provides a strong indication of the likely direction in which we are heading.
SCIENTISTS INVOLVED IN THE STUDY
William W. L. Cheung, Fisheries Centre, University of British Columbia
Jorge L. Sarmiento, Atmospheric and Oceanic Sciences Program, Princeton
John Dunne, Geophysical Fluid Dynamics Laboratory (NOAA)
Thomas L. Frölicher, Atmospheric and Oceanic Sciences Program, Princeton
Vicky W. Y. Lam, Fisheries Centre, University of British Columbia
M. L. Deng Palomares, Fisheries Centre, University of British Columbia
Reg Watson, Fisheries Centre, University of British Columbia
Daniel Pauly, Fisheries Centre, University of British Columbia
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