Five Ways Climate Change Threatens the Future of Fish

Fish, like people, have preferred temperatures where they like to live. As oceans warm, fish are moving into deeper waters or poleward to stay within their comfort zones. When fish move, the new distributions can have big impacts on the coastal communities that have traditionally relied on those fisheries. For example, fish populations may relocate across a state or national borders, and no longer be legally accessible to some fishers. This can cause significant financial impact to local communities and nations, as income from access licences may decrease—such as with yellowfin tuna in the Pacific. In addition, as fish move deeper and farther, fishing may become more expensive and traditional methods for catching fish may not work. The decrease in numbers of locally available fish requires more adaptive management, which is often lacking, and can result in increased illegal fishing as fishers attempt to maintain livelihoods.

Coral reefs are the rainforests of the sea, providing shelter, spawning grounds, and food for about 25% of the world’s fish species. Warming and acidifying seas, the result of too much CO2, are a double whammy for corals, which are undergoing massive declines around the world. Recent back-to-back bleaching events in the Great Barrier Reef, for example, has reduced the number of coral babies by 89%, painting a grim picture for recovery. Globally, the pattern repeats, with mass bleaching events compounding the decline in reef health due to overfishing and other factors. Other critical habitats are similarly at risk, including kelp forests. Collapse of these ecosystems poses significant threat to food security for millions of people that depend upon reef fisheries for subsistence and trade, as well as risks loss of valuable medicinal resources that are only just now being discovered and used to fight diseases such as cancer.

Warming oceans will lead to less primary production, which will result in overall less biomass (amount of animals and plants per area) in the sea. And, for the individuals that do remain, they are likely to be smaller because of less food. Models predict that for every 1 degree Celsius of warming in the ocean, we will have on average 5% less biomass. This means that while some places may see an increase in biomass due to shifting location of some species (see #1), across the globe the amount will decrease. This loss will be most pronounced for top predators in the food chain—species like tuna, grouper, and salmon that humans rely on for food. The size of marine species, especially shellfish, are also likely to be affected by the rising acid levels in the oceans.

Sea level rise and increasing impact of storms are wreaking havoc on coastal communities —many of which are most dependent on healthy fisheries for food and income. As the devastation from unprecedented fierce hurricanes attests, climate refugees are growing in number and in need, the result of these compounding effects.

Many Indigenous populations live in areas that are most susceptible to the effects of climate change (including coastal areas), and face loss not only of food and trade routes, but also tradition due to rapidly changing climate. “Cultural trauma” is an often overlooked but profound potential impact of climate change, especially for cultures with deep, historic ties to the coast, sea, and fisheries.
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Many of the effects of climate change on the oceans are still being researched and discovered. What we know now is that the impacts aren’t going to be evenly felt worldwide. Some areas will likely benefit from more or bigger fish, but the big question is how we can mitigate the effects for the communities who lose access to fisheries resources (and so much more) as a result of these climatic shifts.

Climate change is a crisis for fish and our oceans, but it’s a crisis we can all act on. You can start by getting involved with the Climate Strike this Friday. In the next blog post, we will share more about some of the innovative work being done to mitigate these risks. While limiting carbon emissions (and quickly) will of course be vital overall, so will work to adapt to the changes that are on the way. There is much at stake, and all our talents, voices, and efforts are needed to secure a future full of fish.