WWF: the consequences of overfishing

Losing Nemo: Creatives around the world tell the story of the dying oceans


Before the modern industrial era, our oceans were actually CO2 sources and the atmosphere was a carbon sink. In 200 years, we have reversed that entire cycle. It’s not hard to see why. Every year, we burn 9.1 petagrams of fossil fuel. To give you an idea how much that is, it’s equivalent to the amount of coal in a coal train wrapped around the planet 63 times says Chris Sabine, director of the Pacific Marine Environment Laboratory at the National Oceanic and Atmospheric Administration (NOAA).  This burning causes us to dissolve 22 million metric tons of CO2 into the ocean each and every day.

Alongside the dramatic reversal of the carbon cycle, scientists are observing a commensurate increase in the acidity of the oceans, greater fluctuations in temperatures, and an increase in oxygen depleted waters – a phenomenon known as hypoxia.

Our oceans are under a multitude of threats:

  • 30% increase in acidification since pre-industrial times due to increased absorption of anthropogenic CO2 which threatens a multitude of dimensions of ocean health from coral reefs to algae growth, potentially threatening the entire food chain if critical species of plankton cannot form carbonate shells
  • Hypoxia and reduction of O2 levels
  • plastic pollution – plastics in the ocean breaking down into micron size particles with unknown effects on the biotic environment
  • Overfishing has decimated 90% of the global fish stocks. What will this do to the balance of living creatures in the ocean is unpredictable
  • Global warming melting of glaciers, Greenland and ice will result in significant changes in sea level, ocean salinity and temperature zones. In an extreme event, the ocean’s conveyor belt, the thermohaline cycle can potentially even stop moving.

A short film on oceanic research in Argentina being conducted by Alberto Piola

Can Overfishing decrease Oceanic Carbon Sinking Capacity and Fertility?

Overfishing is just one of the many problems our oceans face. However, in an unexpected twist, a Canadian environmentalist proposes a novel new theory which claims that overfishing may play a significant role in reducing the carbon sinking ability of the oceans.

Canadian environmental activist Debbie MacKenzie has lived on the east coast of Canada her whole life. MacKenzie grew up on the coast and her own upbringing is rich with encounters with ocean flora and fauna. Her own rich history of experience serves as a metric for the enormous change she has observed in her lifetime. The East coast was once home to a thriving cod fishing industry which collapsed dramatically. Alarmed by the disappearance of an entire industry, MacKenzie has become intrigued by the causes. The detailed theory she has formed is based on compelling personal evidence combined with an in-depth knowledge of practical and theoretical marine biology and forges a surprising link between overfishing and the oceans ability to sink carbon. Fish lift nutrients to the surface water, fertilizing algae and powering a natural carbon sink. But our massive removal of fish, sea birds and marine mammals over centuries has sabotaged this carbon sink, like deforesting the land. If sea animals made a comeback, the fish-powered carbon sink would mitigate atmospheric carbon dioxide. But this idea – that fish boost ocean carbon uptake, and that science has overlooked it – challenges accepted ideas and threatens the fishing industry.

MacKenzie observes that ocean life is dying back in unexpected ways:

  1. Even though there are fewer fish and other sea animals, more of them are starving
  2. Primitive microbes are increasing their impact on ocean life: waves of ‘sickness’ are spreading:
    • ‘dead zones,’ harmful algae blooms
    • diminished presence of sea animal life in general
  3. When the cod fisheries collapsed in Eastern Canada, zooplankton populations also went into dramatic and unexpected decline.
MacKenzie believes that failing ocean fertility induced by fishing is the cause. While mainstream ocean scientists hold that ocean productivity is not a concern, Mackenzie cites overwhelming evidence across the entire spectrum of fisheries that species are growing at dramatically slower rates. MacKenzie says ” Besides the flattened belly profile, the cod starving in the wild shows an unusually downturned head and reddened mouth as it appears to struggle to survive by bottom feeding at a size when it would normally rely largely on prey fish in the water column. This physical sign that adult cod are now struggling to survive by bottom feeding contradicts several current lines of thinking about the reasons for poor growth in cod today (e.g. cooler water depresses appetite, fish are genetically slower growing, excess seal predation is killing them…). A simple shortage of their normal prey appears to be the most immediate problem facing Atlantic cod.”


Starving Ocean: Where Have the Fish Gone?

Debbie MacKenzie talks to Bedford Institute of Oceanography