By: Robert Burmeister
Most of what we know about anything in life is molded and restricted by the barrier of our own perceptions and perspectives. This applies to life itself. Without knowing who you are, I can say with almost 100% certainty that you’ve spent your whole life on the ground just like me; so, when you and I think about the world and the life that occupies it, we tend to think of land-based life before we do marine life. This is in spite of the fact that Earth is mostly water and complex multicellular life evolved in the oceans before staging a terrestrial conquest. Even now – hundreds of millions of years after life made the transition from wet to dry – the oceans still have an influence on this open-system planet and the life on it that cannot be understated. This understanding of the relationship between ocean stability and land-based life, as well as human economies, is why recent news of decreasing fish populations is so worrying.
The study at the center of this recent recession is the Science journal article “Impacts of historical warming on marine fisheries production,” and it has made splashes across the media and the marine sciences. The implications this study are global, as the authors implemented a dynamic population model to measure the effects of ocean temperature on 235 fish and invertebrate populations – representing 124 species and about 33% of the total global catch (Free, C.M., et al., 2019). When using this dynamic population model in tandem with a hindcast of maximum sustainable yields (also known as MSY, the upper recommended limit for fisheries to make a profit while conserving fish populations) from 1930-2010, Chris Free and his co-authors determined that there has been a 4.1% decrease in fish populations across eight decades. To put that into perspective, Free likens this to “1.4 million metric tons of fish,” as quoted in The New York Times article “The World is Losing Fish to Eat as Oceans Warm, Study Finds,” by Kendra Pierre-Louis. Considering that, as Pierre-Louis puts it, “fish make up 17 percent of the global population’s intake of animal protein, and as much as 70 percent for people living in some coastal and island countries,” (according to the UN’s Food and Agriculture Organization) and you can see why such a study would ring so many alarms — especially as human population is on the rise and all of these new people will need food based on sustainable sources (Food and Agriculture Organization (FAO) of the United Nations, 2016).
Much anxiety has been expressed regarding the rising of the oceans and the consequences that it will have for coastal cities and island-nations; however, the world’s oceans are an incredibly complicated open-system in which numerous consequences arise from little things, such as slight changes in temperature or pH levels. According to Free et al., warmer oceans have a negative impact on many fish populations by stratifying populations toward the poles. These populations are stratifying for a number of reasons, and a chief one is that warmer oceans are causing a cascading effect on zooplankton, which in turn reduces the amount of larval fish that will survive and mature. Some of the kinds of fish most affected by the warming of the oceans include codfishes and herring, as the stratifying trends observed by Free et al. often fall within taxonomical lines – that is to say, fish in the same genus, family, order, etc. Free et al. also cites overfishing as having a magnification effect on those ecoregions already suffering losses in fish populations. Additionally, the warming of the oceans will lead to less oxygen being available to marine life, as warmer seawater does not allow for as much oxygen concentration as cooler seawater does (Keeling, R.E., Körtzinger, A., & Gruber, N., 2010). Free et al. mention that some ecoregions – such as the Labrador-Newfoundland Sea, Baltic Sea, Indian Ocean, and Northeast U.S. shelf – have actually seen positive effects of warming, but this is small compensation for those ecoregions seeing huge losses; those ecoregions most negatively affected are the Sea of Japan, the North Sea, Iberian coastal waters, the Kuroshio Current, and the Celtic-Biscay Shelf. Many of those latter ecoregions are important to East Asia, which both rely heavily on seafood and are some of the fastest-growing human populations in the world (Free et al., 2019).
This is all scary news, but more than being scary – it is real, and demands immediate action to be taken if humanity wants to continue to reap the benefits from the sea in the future as we have done for uncounted millennia. What can be done, if hope remains for anything to be done at all? Well, I do have some good news for you: the effects of climate change on fisheries can still be mitigated by improved management of these fisheries. By taking climate change adaptation into account to tackle both “productivity and range-shift challenges,” (i.e. by working to lower the MSY appropriately compared to related fish populations) gains of 60% in biomass, 34% in harvest, and 154% in global profit can be attained (Gaines et al., 2018). However, proactive change will have to come quickly, as the effects of climate change on the world’s oceans and its fish populations are already being seen, and nobody is quite sure how the 2020’s will pan out for both people and fish alike.
Our ancient aquatic animal ancestors made landfall and the change to terrestrial living some hundreds of millions of years ago; humanity has depended upon the bounties of the sea for some tens of thousands of years. In this context, humanity has lived and died by the oceans; it is quite clear now that if we don’t adapt to the changing ocean, we will slowly, but surely, die. The time has come when we are cognizant of our effects – both direct and indirect, positive and negative – on the waters of the world, and we possess the ability to change our ways for the better. And we have no good reason not to do so, other than it being hard. Yes, changing the ways that we fish and changing other aspects of our lives which negatively impact our oceans is going to be hard. Harder than living in a chaotic world where we have no control and are assailed by our past mistakes, however, it will not be.
Free, C.M., Thorson, J.T., Pinsky, M.L., Oken, K.L., Wiedenmann, J., & Jensen, O.P. (2019). Impacts of historical warming on marine fisheries production. Science, 363(6430), 979-983. doi:10.1126/science.aau.1758
Gaines, S.D., Costello, C., Owashi, B., Mangin, T., Bone, J., Molinos, J.G…Ovando, D. (2018). Improved fisheries management could offset many negative effects of climate change. American Association for the Advancement of Science 4(8), n.p. doi:10.1126/sciadv.aao1378
Keeling, R.E., Körtzinger, A., & Gruber, N. (2010). Ocean deoxygenation in a warming world. Annual Review of Marine Science 2, 199-299. doi:10.1146/annurev.marine.010908.163855pmid:21141663
Pierre-Louis, K. (2019, Feb. 28). The world is losing fish to eat as oceans warm, study finds. The New York Times. Retrieved from https://www.nytimes.com/2019/02/28/climate/fish-climate-change.html
Food and Agriculture Organization (FAO), “The state of world fisheries and aquaculture 2016” (Food and Agriculture Organization of the United Nations, 2016).