Things are looking grim for fish and other animals that live in the world’s oceans. According to a recent comprehensive study, overall populations of marine mammals, birds, reptiles and fish have decreased by half in the past four decades. Worryingly, the report also highlighted that many species of fish commonly eaten by humans were seeing some of the greatest declines.
The study data showed that over-fishing, pollution and climate change had decimated the size of key commercial fish stocks between 1970 and 2010, in some cases stocks were down by as much as 75%.
More on rapidly declining ocean populations
The new research by conservation group WWF and the Zoological Society of London examined 5,829 populations of 1,234 species of marine animals over a 45 year period, and found an overall 49% decrease in populations. The study attributes the large majority of these population losses to over-fishing and habitat loss.
Some marine species used for food are the worst off. The Scombridae family of fish (includes tuna and mackerel) have declined by nearly three quarters (74%).
Sea cucumbers are one of the most dramatic examples of a man-made decline, with a 98% population drop off in the Galapagos and a 94% decline in the Egyptian Red Sea in less than a decade.
Loss of habitats for marine animals is another major problem. The WWF / ZSL study shows that 29% of seagrass area, which is critical for food, stabilizes the seabed and provides a nursery for many species, has disappeared since 1879, and the mangrove cover has declined by more than 20% since 1980.
Climate change is also impacting the oceans, with a greater amount of carbon dioxide being absorbed into the oceans, making them more acidic and hurting species with shells. Warming seas are also shrinking coral habitats and many species of marine animals are having to leave their usual ranges.
Experts note that the marine population declines were at their peak in the 1970s and 1980s, as improved technology led to over fishing, but have stabilized in most cases since 1990. That said, the report noted there is growing evidence of a new wave of marine population drop offs in the past few years.
Wildlife biologists have been warning for some time now that many marine populations were not recovering for a variety of reasons related to human activity, and this new study offers yet more support for this conclusion.
Statement from the Zoological Society of London
Robin Freeman, the head of indicators and assessments at ZSL, noted: “This is a wake-up call, but it’s also an opportunity. These are populations that are smaller than they would be, and should be. They aren’t recovering.”