Hot Topic: Effects of Climate Variability on Fisheries
Part C: Long-Term Variability: Sockeye Salmon
As you've seen to this point, short-term climate variations often occur in cycles. In most cases, when climatic conditions returned to "normal", fishing conditions and landing totals also rebounded. But what consequences might accompany a steady one-directional trend in climate change? Specifically, how might global warming affect fisheries?
- Read the World Wildlife Fund report Are we putting our fish in hot water? (Acrobat (PDF) 1MB Nov20 07) to learn about the potential long-term effects of global warming on the world's fisheries.
Answer the following questions to check your understanding of the information contained in the World Wildlife Fund report.
- According to the report, by how much are global temperatures expected to rise by the end of the century? 1.4-5.8 °C
- Why are fish more sensitive to temperature changes than many other animals?
- How might increased ocean temperatures impact aquaculture? Aquaculture may suffer as certain areas lose the ability to culture species that they currently farm. For example, a temperature increase of only 1 °C could devastate the US$100 million catfish industry in the southern US by shifting the southern limit of viable catfish production 240 km north, away from dependent local communities and established infrastructure.
A recent study explored the potential implications of long-term climate change on the distribution of Alaska sockeye salmon. The distribution of sockeye salmon is limited by ocean temperature. In cold-blooded animals (such as fish), base metabolic rates increase exponentially with increased temperaturesfish burn calories faster in warmer water. Fish can typically grow faster in warmer water, but only if food is plentiful enough to sustain the increased calorie needs that accompany a higher metabolism. Sockeye move into warmer waters as food levels increase seasonally. But what would happen to sockeye distribution if water temperatures increased permanently?
- According to the report, by how much are global temperatures expected to rise by the end of the century?
- Look at the images below of the distribution of Alaska sockeye salmon in winter and summer. The red and light blue regions show current distributions of Alaska sockeye salmon in winter and summer. The red areas alone represent the regions in which ocean temperatures would be suitable for sockeye salmon if ocean temperatures were to rise in response to a doubling of the current atmospheric carbon dioxide level.
Image credit: Welch, D., Y. Ishida and K Nagasawa. 1998. Thermal Limits and Ocean Migrations of Sockeye Salmon (Oncorhynchus nerka): Long-term Consequences of Global Warming. Canadian J. of Fisheries and Aquatic Sciences. 55:937-948. Image source: NOAA.
Stop and Think
1:Estimate what fraction of the sockeye salmon's winter and summer habitats could be lost if current atmospheric carbon dioxide levels are doubled.
2:Discuss possible impacts of global warming on the marine food chain, including humans and other land animals that rely on the oceans for food.