Optimism for fisheries under climate change

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:

For example, until 2009, North East Atlantic mackerel was well managed under a trilateral agreement between Norway, the Faroe Islands, and the European Union. However, because of shifts in migration patterns, Iceland suddenly became a key contender in the fishery and maximized its newfound access to a valuable fishery. Since countries could not agree on appropriate quota allocations, management was compromised. By 2010, mackerel harvest was 40% above safe biological recommendations.

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:

  1. Full adaptation to climate change (both fish migration & productivity changes)
  2. Range shift adaptation only (management only for fish migration)
  3. Productivity adaptation only (management only for productivity shifts)
  4. 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.

Productivity:

From Gaines et al. 2018. Percent change in MSY under RCPs 2.6, 4.5, 6.0, and 8.5. Each line represents an individual stock. The red dashed line indicates global percent change (weighted mean) in MSY. Gray lines represent change in MSY for all 915 global stocks.

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.

Migration:

F2.large
From Gaines et al. 2018. Percentage of species stocks that move into, out of, or both into and out of one or more countries’ EEZs by 2100 for each RCP.

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

From Gaines et al. 2018. Percent difference in biomass, harvest, and profit relative to today across RCP scenarios.

The authors do a nice job to sum up the figure:

While these results show that adapting to climate change delivers far better outcomes than not adapting, we can also compare future outcomes to what is obtained today. Even in the presence of the net negative effects of climate change, the Full Adaptation policy could deliver higher total profit, harvest, and biomass (increases of 27, 16, and 29%, respectively) than what the oceans provide today.

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.

Gaines et al. 2018 was co-authored by several scientists, including some from the Environmental Defense Fund (EDF). There is additional information about the paper on EDF’s website, here.

Max Mossler

Max Mossler

Max is the managing editor at Sustainable Fisheries UW. He thinks a lot about how environmental perception influences environmental policies.

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