Sea turtles, some of the most majestic, gentle creatures in the oceans, are having a rough time of it. Though not typically targeted by fishermen, the animals often become entangled in nets or hooked on long lines, and end up as bycatch that is either eaten or tossed like trash back into the sea.

Measuring how many turtles die this way every year is a crucial task; in some places turtle populations are being devastated by the effects of bycatch. It isn't easy; fishing practices around the world are chronically under-reported. But in an attempt to shine light on the situation, researchers, led by Bryan Wallace of Conservation International, have compiled the first global map of sea turtle bycatch.

Published in a recent issue of the journal Conservation Letters, the map breaks down incidents of turtle bycatch by the type of fishing gear used:

In all, the records indicate about 85,000 turtles per year were accidentally caught worldwide between 1990 and 2008 (each dot represents a study with data on bycatch rates). That may not sound like much, but the team estimates that only about one percent of all fishing activity is reported, meaning a more likely estimate for the number of turtles that die annually is at least 100 times that figure, or around 8.5 million turtles.

"Bycatch is the most serious and acute threat to sea turtles globally," Wallace told Discovery News. "It's an extremely pervasive pressure on sea turtle populations. In some cases it is a main driver for significant population declines and even collapses."

As prolific grazers, turtles are incredibly important species for marine ecosystems. "Green turtles in the Caribbean, west Indian Ocean, southwest Pacific, etc. are like the bison of sea grass," Wallace said.

Hawksbill turtles munch sponges and help keep coral reefs healthy, and many other species eat jellyfish. Their egg-laying habits infuse beaches with nutrients, and their trans-ocean migratory patterns tote small critters to far-flung habitats.

It's hard to overestimate how important sea turtles are to a healthy marine ecosystem. With this map, we may finally be able to gauge the huge impact we are having on their populations, and take steps to reverse it.

Images: Bryan Wallace