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Dead fish on the coastline (Image: Steve Hillebrand / U.S. Fish and Wildlife Service)

Dead fish on the coastline (Image: Steve Hillebrand / U.S. Fish and Wildlife Service)

Over the past seven decades, large numbers of species have been dying with increasing frequency.

That’s according to a new study published Monday in the Proceedings of the National Academy of Sciences, in which researchers studied mass mortality events (MMEs) for animals between the years 1940 and 2012. In the study, an MME is defined as a rapidly occurring catastrophic event that kills over 90 percent of a population, results in the death of more than one billion individuals or produces 700 million tons of dead biomass in a single event. “Such events can reshape the ecological and evolutionary trajectories of life on Earth,” the authors wrote.

The study examined 727 MMEs from the 1940-2012 period and found that birds, marine invertebrates and fish experienced greater numbers of mass die-offs the closer the timeline approached the present day. The same trend was not observed for mammals, whose numbers remained relatively unchanged, or for reptiles and amphibians, who actually saw a decrease in MMEs.

The three primary factors in the die-offs were disease, biotoxins and man-made disturbances, such as overfishing.

According to the Food and Agriculture Organization, one-third of the ocean’s fish stocks are over-exploited (some sources claim it’s over 50 percent). This is despite the fact that almost every country has ratified the UN Convention on the Law of the Sea (UNCLOS), what Tommy Koh, a former president of UNCLOS, has called the “constitution for the oceans.” The UN as well has a fish stocks agreement, but, according to Business Insider, only 80 countries have ratified it and 28 of them are failing to meet most of its requirements.

Illegal and unreported fishing is worth between $10 billion and $24 billion a year.

Image Credit: The Economist

Image Credit: The Economist

Meanwhile, climate change is also affecting the world’s oceans. Producing about half the planet’s oxygen and absorbing 25 percent of its carbon dioxide, the ocean is simultaneously warming and acidifying at the fastest rate in 300 million years. A forthcoming report from the UN’s Intergovernmental Panel on Climate Change shows that chlorophyll concentrations in the oceans have fallen roughly 10 percent since 1998 in the North Pacific, Indian and North Atlantic Oceans – potentially due to the lower nutrient level in the water caused by upwelling of warmer water and the sinking of colder water. At the same time, populations are decreasing for 90 percent of the zooplankton found in Norwegian waters.

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