What is Harming the Ocean More: Climate Change or Overfishing?

Question: What's a more immediate threat to the health of our oceans at the moment: climate change or overfishing? -Van, Georgia

Answer: Our ocean and the marine life that call it home face many threats, including not only climate change and overfishing, but habitat destruction, pollution, and more. Last month alone, I saw news stories of toxic algal blooms killing endangered fish and record heat harming salmon and other marine life. So what’s the biggest threat?

As with many scientific questions, the answer is “it depends.” It depends on what scale you’re looking at, and what marine life you’re focusing on—the biggest threat to manatees (boat strikes) is not the same thing as the biggest threat to angel sharks (being caught as bycatch). But you asked about the whole ocean, and you asked about in the short-term.

Climate change is not a far-off problem, it’s here already—those salmon and other marine animals suffering from a recent heat wave that was climate change induced. Climate change’s worst impacts, however, aren’t here yet. Climate will make habitats unlivable for many marine species, including ecologically important species and those we depend on for food. It may be the death knell for many coral reefs, on which so many unique and beautiful species depend. It is already causing large marine life to move into new habitats, with unknown consequences for the animals already living in the places to which they are migrating. And don’t forget about ocean acidification, “climate change’s evil twin,” which will change the very pH of the ocean so that, among other things, shelled organisms cannot build their shells. Climate change is, in short, extremely bad news for the ocean and the animals that live there.

Overfishing and associated unsustainable fishing practices mean that we aren’t just taking too many fish out of the sea, but we’re also having indirect harmful impacts on other ocean animals (through bycatch) and on habitats themselves. Increasingly large and powerful fishing vessels mean that few parts of the ocean are safe from humans simply because they’re inaccessible to us. When overfishing is allowed to continue and fisheries collapse, this is devastating not only ecologically, but for the humans who depended on that fish stock for food security and livelihoods.

So what’s a greater threat to the oceans? I want to stress here that both are extremely bad and we need to focus on solving both, as well as other threats to the ocean. I also want to stress that everything is connected, and climate change (including the aforementioned tendency of species to move in response to climate change) will impact overfishing.

Overfishing is, in my professional opinion, the greatest short- and medium-term threat to marine biodiversity. While many of the worst impacts of climate change aren’t here yet and the impacts that are here aren’t global in scope yet, many of the worst impacts of overfishing are here now, are already worldwide in scope, and are already affecting entire ecosystems and the humans who depend on them for food and jobs.

The good news is that folks claiming that overfishing is such a big problem that we all need to give up all seafood immediately are not correct, and science-backed sustainable seafood absolutely exists. But it’s no accident that non-profits like the Environmental Defense Fund call overfishing “the greatest threat to the ocean," or what we regularly see articles like 'Overfishing is a Worse Threat to the Ocean than Climate Change.’ And it’s no accident that I’ve chosen to work for an environmental non-profit that focuses on ending overfishing.

Ask a Marine Biologist is a monthly column where Dr. David Shiffman answers your questions about the underwater world. Topics are chosen from reader-submitted queries as well as data from common internet searches. If you have a question you’d like answered in a future Ask a Marine Biologist column, or if you have a question about the answer given in this column, email Shiffman at WhySharksMatter@gmail.com with subject line “Ask a marine biologist.”

Dr. David Shiffman is a marine conservation biologist specializing in the ecology and conservation of sharks. An award-winning public science educator, David has spoken to thousands of people around the world about marine biology and conservation and has bylines with the Washington Post, Scientific American, New Scientist, Gizmodo and more. Follow him on Twitter, Facebook and Instagram, where he’s always happy to answer any questions about sharks.

The views expressed in this article are those of David Shiffman, and not necessarily the views of Sport Diver or Scuba Diving magazines.