Viewers of the various "extreme angling" TV shows have likely already heard that it's getting more and more difficult to find big fish in the world's lakes and rivers. A new international study, however, now confirms that there has recently been a drastic decline in populations of large freshwater animals.

Led by scientists from Germany's Leibniz-Institute of Freshwater Ecology and Inland Fisheries, the study looked at data relating to global populations of freshwater megafauna, gathered worldwide between 1970 and 2012. The 126 species that were counted within that period included 30-kg-plus (66-lb) animals such as river dolphins, beavers, crocodiles, giant turtles and sturgeons.

Overall, it was found that freshwater megafauna populations declined by a shocking 88 percent throughout the 42-year time span. This was twice as high as the loss of vertebrate populations on land or in the sea during the same period.

Regionally, the numbers were highest in the Indomalaya biogeographic realm (South and Southeast Asia, and southern China) and the Palearctic realm (Europe, North Africa and most of Asia), at 99 and 97 percent respectively. As far as the worst-hit species go, there was a 94-percent decline in large fish such as sturgeons, salmonids (salmon, trout, char, etc) and giant catfishes, followed by a 72-percent decrease in aquatic reptiles.

The biggest culprit in the loss appears to be overexploitation, as the animals were killed for their meat, skin, or fur (or their eggs were harvested) faster than they could reproduce. Additionally, the ever-increasing damming of rivers played a large role, keeping species from reaching their feeding and spawning grounds.

It was also noted, however, that conservation efforts in recent years have led to the stabilization or even increase of 13 megafauna species. These have included the green sturgeon and American beaver in the US, and the Irrawaddy river dolphin in Asia's Mekong basin. Additionally, although political differences between bordering countries have made conservation difficult in Europe, the Eurasian beaver has been reintroduced to regions where it was once found, while efforts are also underway to reintroduce two species of sturgeon.

A paper on the study, which was recently published in the journal Global Change Biology, suggests that further conservation efforts are very much needed.