The study uses a Living Planet Index based on trends in 5,829 populations of 1,234 mammal, bird, reptile and fish species in the ocean.
According to the report
, populations of locally and commercially fished species have also fallen by half, and some even more. The tuna and mackerel populations have seen a nearly 75% decline and Bluefin tuna in the Pacific are on the brink of extinction. This is largely due to the global problem of overfishing, the authors said.
All the world's oceans are at risk, but the Pacific Ocean is of particular concern. There are fewer regulations in Asia, and they are fishing more waters. The common practice of "shark-finning" has taken a toll on the shark population. This involves only removing the fins from the shark, and throwing the body back. Shark-fin soup is considered a delicacy in Asia. However, if this continues, an estimated 25% of shark species could become extinct in the next 10 years.
Many of the species that are dying are vital food sources around the world -- especially for poorer countries who rely primarily on the fish population for food. Also, the ecology of the oceans is greatly impacted.
The report blamed several factors for the decline.
One problem is a decline in fish habitats. Many of the mangroves and sea grasses have been lost. In fact, mangroves are being lost two to five times faster than forests. Also, the oceans' tropical reefs have decreased by half and could all be lost by the year 2050. Much of this is due to warmer waters and acidification. Over 25% of ocean marine life lives on coral reefs and roughly 850 million people directly benefit from them -- the loss of coral reefs could be catastrophic, according to the report.
A second problem is pollution. There is 250,000 metric tons of plastic in the oceans. Plastic harms smaller fish that bigger fish rely on for survival and may also harm larger fish and mammals who become tangled or trapped, resulting in suffocation.
Related to pollution is climate change, which is responsible for changing the oceans more rapidly than at any other point in recorded history. A slight rise in temperature will change ocean currents and increase acidity levels. A slight temperature increase will also disrupt the ocean's food chain. Species will alter their migratory patterns in search of cooler water, which will only further unbalance the world's oceans.
"The ocean is a renewable resource that can provide for all future generations if the pressures are dealt with effectively," said Marco Lambertini, director general of WWF International. "If we live within sustainable limits, the ocean will contribute to food security, livelihoods, economies and our natural systems."
Turning the tide
The report also expressed a glimmer of hope regarding how to reverse these devastating findings. It highlights the importance of protecting marine habitats, managing fisheries, and improving fishing practices.
"The good news is there are abundant opportunities to reverse these trends," said Brad Ack, senior vice president for oceans at WWF. "Stopping black market fishing, protecting coral reefs, mangroves and other critical ocean habitats, and striking a deal in Paris to slash carbon pollution are all good for the ocean, the economy, and people."
"Now is the time for the U.S. and other world players to lead on these important opportunities."