Australia's Great Barrier Reef has lost 50% of its coral since the mid-1980s, much of that because of a ravenous species of starfish that can each consume some 12 square yards (10 square meters) of coral in a year, scientists reported Tuesday.
According to a study by the Australian government's Institute of Marine Sciences and the University of Wollongong, the coral cover on the world's largest coral reef ecosystem suffered damage from tropical cyclones (48%), the crown-of-thorns starfish (42%), and coral bleaching (10%).
If current trends continue, the reef will lose another 50% of its coral in the next 10 years, the scientists said.
Stopping the starfish infestation is the one thing humans can do that can save the reef, they said.
"We can't stop the storms, and ocean warming (the primary cause of coral bleaching) is one of the critical impacts of the global climate change," John Gunn, chief executive officer of the institute, said in a press release. "However, we can act to reduce the impact of crown of thorns."
"The study shows that in the absence of crown of thorns, coral cover would increase at 0.89% per year, so even with losses due to cyclones and bleaching there should be slow recovery," Gunn said in the release.
Reacting to the study, the World Wildlife Fund said Australia must reduce fertilizer runoff as a first step to controlling the crown-of-thorns starfish.
Tens of thousands of dead fish have washed up on a 25-mile stretch of Lake Erie's northern shore, and Ontario environmental officials say they could be victims of a natural phenomenon called a lake inversion.
The inversion brings cold water, which has lower oxygen levels, to the lake's surface and fish suffocate.
"Essentially it's a rolling over of the lake," Ontario Ministry of the Environment spokeswoman Kate Jordan told The Chatham Daily News. "Something - whether it be a storm, or cooler temperatures at night, or strong winds - triggers a temperature change in the lake."
Jordan said it was windy and choppy on the lake Friday night, according to a report in The Windsor Star. The fish kill was reported Saturday.
A Chinese city has canceled a $157 bounty on piranha after people killed too many other fish in a four-day hunt, Chinese state media reported Friday.
Government officials in the southern city of Liuzhou had offered a 1,000-yuan ($157) reward for every piranha caught after at least three of the sharp-toothed fish attacked two swimmers in the Liujiang River over the weekend, biting off parts of one person's finger, state-run agency Xinhua reported.
But no one caught any piranha in the four-day river hunt, according to the state-run China Daily newspaper.
And too many local fish breeds were being killed, including in nets, prompting concern about the river's ecological balance, the head of the local fishery bureau told China Daily.
Editor's Note: This post is a recap of the top five videos on CNN.com from the past week. So in case you didn't catch our best videos during the week, here is your chance to see what you missed.
This week's top videos ranged from bizarre, to humorous to just plain tragic. From crazy sea creatures to ogling royals to a heart-wrenching rescue, here are this week's five most popular videos.
Was the royal bosom ogled? CNN's Jeanne Moos reports on men caught up to their eyeballs in cleavage.
A woman shot with a Taser by a trooper in Florida, falls into a coma. Jane Velez-Mitchell speaks with her parents.
Check out this strange fish found in a Chinese market, which one man thought had wings and legs.
New Jersey Gov. Chris Christie says if Warren Buffett wants to pay more taxes, he can just write a check
The stranger who rescued a malnourished teen lying on the side of the road speaks with CNN's Brooke Baldwin.
It's too early to call the rescue near Cape Cod a success, but it looks like there's good news for a fifth of the dolphins that began washing ashore on the Massachusetts coast earlier this month.
The majority of the dolphins rescued during the "mass strandings" have survived and appear to be tooling about off the coast of Maine, according to a news release from the International Fund for Animal Welfare.
Rescuers put satellite tracking tags on six of the 24 animals that they have rescued and released since January 12, when rescuers began finding dozens of common and Atlantic white-sided dolphins along a 25-mile stretch of shoreline.
As many as 100 dolphins may have been stranded during the episode, 50 of which were dead when they were discovered, wrote IFAW senior program coordinator A.J. Cady earlier this week. Three of the dolphins with tracking tags died after being released.
"We're all exhausted, muddy and unsure what tomorrow will bring," Cady wrote Tuesday, "but rest assured, if more dolphins strand, we'll do everything in our power to rescue and release them into open ocean."
Fancy a $50 piece of sushi?
That's what one piece of a 593-pound blue fin tuna sold Thursday at Tokyo's Tsukiji fish market for a record $736,000 is worth.
Kiyoshi Kimura, who runs the Sushi-Zanmai chain in Japan, bought the record-setting fish at the first auction of the new year at Japan's main fish market, a popular tourist stop in Tokyo, according to the Tokyo Times.
The previous record for a fish was set at the market in 2011's first sale of the new year, when a Hong Kong restauranteurÂ paid $422,000 for a blue fin. He took that fish to Hong Kong.
Kimura said he wanted to keep this year's top tuna in Japan. It was caught off Amori prefecture.
"We tried very hard to win the bidding, so that we could give Japan a boost and have Japanese people eat the most delicious tuna," the Mainichi Daily News quoted him as saying.
Despite the record price Kimura paid, pieces of the prize fish are expected to sell for around $5 in his restaurants.
Tons of dead herring that washed up on a Norwegian beach on New Year's Eve are now gone, and no one is sure how they got there or where they went.
Local resident Jan-Petter Jorgensen told Norway's TV2 he went to look at the thousands and thousands of fish after seeing a Facebook posting about them, according to a report on The Foreigner.
Joregensen said it was fortunate the icy cold prevented the mass of dead fish from raising a stink.
â€śIt is 15 degrees below zero today, so the cold means they donâ€™t smell. Nevertheless, the smell will be pretty intense in the long run,â€ť he said, according to The Foreigner report.
Fishermen may sometimes tell tall tales about the enormous fish that got away, but you've never seen anything like this. These people really did get the catch of a lifetime - and got it all on tape. From animals that shouldn't even be in the water to 40-ton "catches," you've got to watch these unbelievable fishing videos.
Editor's note: Douglas M. Jones of CNN International tagged along as a group of international journalists went "catfish noodling" in a Tennessee lake during the Fourth of July weekend. Here he describes how the outing went.
â€śJust stick your hand down in there further and see if he bites it," Marty told me.
With a determined look on my face I took a deep breath and sunk back under water, using my arm as fish bait.
Earlier that morning, before sunrise, a crew and I met a group of visiting international journalists at their hotel in Atlanta.Â We giggled like kids at the idea of sticking our hands into the mouth of a fish and ripping it out from under the water. FULL POST
The sturgeon are jumping on Florida's Suwannee River and boaters beware.
A 60- to 75-pound sturgeon broke the leg of a 25-year-old woman when it jumped from the Suwanee on Sunday afternoon, the fifth time this year a jumping sturgeon has injured a boater, according to a report in The Gainesville Sun.
Tina Fletcher was a passenger on an airboat when the fish struck her, Florida Fish and Wildlife Conservation Commission officials told the Sun. No one else was injured, according to the report.
Southwest Florida Online reports there have been four other incidents of sturgeon hitting boats and boaters this year, with two people suffering minor injuries.
The Gulf sturgeon can grow up to 9 feet long and weigh as much as 300 pounds, according to the U.S. Fish and Wildlife Service. The fish migrates from saltwater into freshwater rivers to spawn and spend the warm months, according to the agency.
But no one knows why they jump, Southwest Florida Online reports.
"I have seen these encounters referred to as 'attacks,' " Allen Martin, a regional freshwater fisheries biologist, told Southwest Florida Online. "However, these fish are in no way attacking when they jump. They are simply doing what they have been doing for millions of years: jumping."
Hundreds of thousands of fish in the Columbia River are dying from the bends.
That's the layman's explanation. Here's the detailed one.
A large winter snow melt is forcing the U.S. Bureau of Reclamation, which runs the Grand Coulee Dam on the Columbia in Washington state, to increase water flows through the dam. The turbulent water is releasing gases, including nitrogen gas, which is what causes the bends in scuba divers when they surface too quickly. Gas levels have been more than 130% of normal recently, the Seattle Times reports.
"We've easily got hundreds of thousands of dead fish," Bill Clark told the Seattle paper. He works for Pacific Aquaculture, which farms steelhead trout in nets in the river.
Pacific Aquaculture's parent company, Pacific Seafood, says it is losing 100,000 fish a day from the 2.7 million still living on the farm in the river 20 miles south of the Grand Coulee, according to a report on SeattlePI.com.