In what is one of the most substantial reviews of marine species ever conducted, researchers have noticed a strong decline over the last 40 years.

According to The Guardian, the World Wildlife Fund (WWF) and Zoological Society of London (ZSL) collaborated on the newly released "Living Blue Planet Report." The researchers found 49 percent decline of all marine species' populations from 1970 to 2012.

"In less than a human generation, we can see dramatic losses in ocean wildlife - they have declined by half - and their habitats have been degraded and destroyed," Brad Ack, senior vice president for oceans at WWF, told Discovery News. "Driving all these trends are humans actions: from overfishing and resource depletion, to coastal development and pollution, to the greenhouse gas emissions causing ocean acidification and warming."

In the same period, the researchers also noticed about a 75 percent decline among tuna and mackerel populations. The WWF and ZSL hope their report can help conservationists combat the issues causing these heavy declines, including overfishing, pollution, and habitat loss.

"I am terrified about acidification," Louise Heaps, chief advisor on marine policy at WWF in the U.K., told The Guardian. "That situation is looking very bleak. We were taught in the 1980s that the solution to pollution is dilution, but that suggests the oceans have an infinite capacity to absorb our pollution. That is not true, and we have reached the capacity now.

"It's not all doom-and-gloom. There are choices we can make. But it is urgent."