After a summer of scorching wildfires, and in the midst of intense storms across the globe, it’s a difficult time to look at climate change with hope. But, we’re going to—thanks to a new paper, Gaines et al. 2018 (open access), published last week that concluded that improved management could offset many of the negative effects of climate change on fisheries; a well-timed dose of ocean optimism.
But first some background: we know that climate change is going to affect the home range and abundance of commercially important species. Warm water is also going to change the distribution of nutrients (productivity) that produce the phytoplankton at the base of the food chain that fish rely on for food. As the ocean warms, fish will migrate to find the water temperature they are adapted for and/or the food they need to survive. Some species will do well with migration, some won’t. Generally, the total biomass, or amount of fish will remain about the same under warmer ocean temperatures, but the composition, or diversity of fishes will definitely change. Management needs to prepare to reduce fishing quotas on species that will suffer and increase fishing pressure on species that will thrive.
Fish populations will also migrate into, and out of, different exclusive economic zones (EEZs), the areas up to 200 miles off the coast of a country that has exclusive rights to the fish in that area. Fish migration is already causing geopolitical problems and impacting sustainability; from Gaines et al. 2018:
We need proactive and adaptive management to ensure seafood remains sustainable in the face of shifting productivity and migrating fish caused by climate change.
So what did Gaines et al. 2018 do?
Researchers analyzed the climate change implications of over 900 commercially important stocks then modeled their futures under 4 different climate scenarios (representative concentration pathways – RCP) and 4 different management approaches to see what sustainability would be like in the year 2100.
An RCP is a scientifically-backed estimate of radiative forcing (you can think of this as the amount of global warming) based on different emissions scenarios. Basically, an RCP estimates the amount of warming Earth will experience based on the amount of future emissions. It is important to note that RCPs are not climate models—they are scientifically standardized scenarios that can be used to set up models. The 4 recognized RCPs are: RCP 2.6, 4.5, 6, and 8.5.
The 4 different management approaches were:
- Full adaptation to climate change (both fish migration & productivity changes)
- Range shift adaptation only (management only for fish migration)
- Productivity adaptation only (management only for productivity shifts)
- No Adaptation
However, before looking at different management approaches, it is important to summarize the effects of the 4 different climate scenarios on fishery productivity and migration.
You can see that only under the worst climate scenario, RCP 8.5, where people and governments fail to address carbon emissions at all does global maximum sustainable yield (MSY) significantly decline.
Again, RCP 8.5 has the largest and most disproportionate effect on fish migration. However, a realistic (and positive!) perspective on the above figures recognizes that RCP 8.5 is an extremely unlikely scenario. People and governments are starting to seriously address carbon emissions—we are not on track for runaway emissions and climate change. The more realistic scenario is RCP 4.5 or RCP 6.0, which is much better than 8.5, but still not good enough. The planet needs to work towards RCP 2.6 to ensure the best possible climate change outcomes.
Okay, back to management scenarios
The authors do a nice job to sum up the figure:
Basically, fishery management can adapt and compensate for coming climate change impacts to produce a seafood future that is more sustainable, bountiful, and profitable than it is today! However, just because fishery management can improve, doesn’t mean it will. Fishery management is a complex mixing and matching of tools, approaches, and capacity that are dependent on several different factors. We need to start improvement management now. Fishery management improvements now will pay large dividends in ensuring we have the most sustainable ocean we can in 2100.