Last year’s horror flick, Shark Night 3D, tells the tale of a group of college friends who are attacked by sharks while vacationing near a lake. While the premise of the movies is that evildoers intentionally put sharks in the lake to make money, it made me wonder whether a shark could ever actually make its way inland to a lake.
First of all, the lake would need to be somehow connected to the ocean via a river or other body of water deep and wide enough to accommodate the large animal as it travels upstream. Secondly, most sharks can only tolerate saltwater, or at the very minimum, brackish water, so freshwater rivers and lakes are generally out of the question for species such as great white sharks, tiger sharks, and hammerhead sharks.
Bull sharks are the exception to this rule – they can tolerate brackish and even freshwater conditions because of their advanced ability to osmoregulate, or maintain a constant concentration of water in their bodies despite changing salinity levels in the water. This species is known to travel 60 miles upstream in warm rivers like the Mississippi and the Amazon.
North Carolina’s Neuse River has long been thought to harbor bull sharks, and Duke University graduate student Meagan Dunphy-Daly has proven it by tagging several of them there this summer. On one of her research trips, she encountered a 2.5 meter male bull shark swimming in water with a salinity of only 21 ppt (seawater is usually around 35 ppt). Why would a bull shark journey up the Neuse River? Perhaps in pursuit of the dolphins also swimming there, or maybe because the river provides a good nursery area for their pups.
Other than the bull shark, there are at least five species of “river sharks” in the genus Glyphis which have been observed in freshwater rivers in South and Southeast Asia and Australia, but they are extremely rare due to habitat degradation and little is known about them. These are the only purely freshwater sharks that have been discovered.
So, although it seems unlikely that you will ever encounter a shark in a freshwater lake, you might want to keep an eye out next time you're on a river.
Manta rays are one of the most fascinating and unique ocean creatures. As the largest of all the rays, giant manta rays can reach up to 22 feet.
But we have been shocked to discover that Alibaba.com, the world’s largest business-to-business commerce website, with over 65 million registered users, is selling manta ray leather. We are asking you to sign a letter to the president and founder of Alibaba.com to urge this company to stop selling manta ray products.
Today, the world’s manta rays are in trouble, because fisheries are pushing many populations toward collapse. The International Union for Conservation of Nature (IUCN) classifies giant mantas and reef mantas as “vulnerable,” to extinction, and the trends for the majority of manta populations remain unknown.
What’s driving the development of fisheries for manta rays? These animals are prized for several body parts, including their skin, which is made into “leather,” their gill rakers (bony structures inside their gills), which are ground to a powder for traditional Chinese medicine, and their cartilage, which is used as a filler in shark-fin soup. Demand for manta ray parts continues to rise, even though there are available substitutes for manta ray leather, gill rakers have been found to have no medicinal qualities, and cartilage adds no flavor to shark-fin soup.
Only once these products are taken off the market and the overall demand from manta ray parts is reduced do these vulnerable animals have a shot at recovery.
In spite of their formidable size, these ocean giants are not to be feared: they are gentle plankton-feeders that spend their time gliding peacefully through the open ocean of the tropics. There are two species of manta rays, and the chance to see an individual in the wild draws scores of tourists each year to manta ray “hotspots” in locales such as Hawaii, Micronesia, and Mozambique.
Like their shark relatives, manta rays are long-lived and mature slowly. They give birth to live pups every two to three years. These characteristics make manta rays extremely susceptible to overfishing, because populations can be fished out faster than they can be replaced. And once a manta ray population is depleted, it may take decades for full recovery to occur.
If you think that sharks are the scariest creatures in the sea, this post may surprise you.
As we've discussed in the past, the majority of shark attacks are caused by only three species (white, tiger, and bull), yet there are more than 500 species that swim the world’s oceans. So next time you’re swimming in the sea, you may want to keep an eye out for these other, seemingly harmless ocean-dwellers as well.
Did you know that there are over 1,200 species of venomous fish on Earth? They vary in the level of harm they can cause to a human who comes into contact with them, but the stonefish is the deadliest of them all. This fish is found in reef habitats in the Indo-Pacific region, and is called a stonefish because it is able to camouflage itself perfectly among the corals, where it lies in wait for an unsuspecting passing fish. Stonefish have 13 venomous spines that, if stepped on by a human, could be deadly.
There are other marine animals besides fish that can be dangerous as well. The sea wasp, also known as the box jellyfish, is one of the most dangerous jellies, and can be found in the Pacific Ocean around Hawaii, the Philippines, and Australia. Their tentacles can grow up to 10 feet long, and each one has about half a million stinging cells!
Sea wasps use their stinging tentacles to paralyze fish prey, but if they make contact with a human, they can cause paralysis and even death in a matter of minutes. Surprisingly, even a dead sea wasp washed up on a beach can be harmful, because their cells are still able to sting. If you are ever stung by a sea wasp, pour vinegar on the affected area to lessen the effects of the venom.
And remember, terrestrial animals can be just as dangerous as marine ones. The Centers for Disease Control and Prevention and International Shark Attack File reported that between 2003 and 2008, 108 people in the U.S. were killed by cows. That is 27 times higher than the four people killed by sharks during the same period, according to the International Shark Attack File.
This blog post is not meant to scare you from ever going outside again, but rather to draw attention to the fact that there are other potentially dangerous animals in the ocean (and on land), but that sharks always get a bad rap in the media ever since the movie Jaws.
What do you think is scarier than a shark? Tell us in the comments.
Editor's note: Happy Shark Week! All week long we’ve been re-capping some highlights from Shark Week programming. Today we review last night's "Shark City."
Shark Week wrapped up last night with an appearance from this year’s Chief Shark Officer, Andy Samberg, in “Shark City.”
This episode was unique from the others that premiered so far this week in that several sharks were followed within a Bahamian marine protected area, so that viewers were able to get to know these individuals on a more personal level. Shark city seems like the ideal home for these sharks, but many sharks are migratory and this area is unfortunately an oasis in an otherwise dangerous ocean. Even though fishing is not allowed in the reserve, it occurs elsewhere nearby and sharks can become entangled in fishing gear.
Editor's note: Happy Shark Week! All week long we are re-capping some highlights from Shark Week programming. Today we review last night's "How Sharks Hunt."
Sharks have been swimming the world’s oceans for over 400 million years, which has given them plenty of time to evolve into some of the most effective marine predators. There are hundreds of species of sharks, and yet each one has its own preferred prey (fortunately, none of them prefer humans) and also a unique way of hunting.
Last night's episode, "How Sharks Hunt," featured Dave and Cody from Discovery Channel’s Dual Survival series as they explored the various methods that sharks stalk and attack their prey. There was a lot of exciting underwater footage taken by high-tech cameras showing various sharks in hunting mode.
For more info on sharks and their amazing abilities, check out Oceana’s myths versus facts sheet, where we set the record straight on some of the most common (and some of the most unusual) myths about sharks.
Here are a few examples:
Myth: Sharks are all the same.
Fact: Shark species are incredibly diverse with very different sizes, shapes, habitats, diets and behaviors. There are approximately 500 shark species, but only three (white, tiger and bull) are responsible for the majority of all bites.
Editor's note: Happy Shark Week! All week long we'll be re-capping some highlights from Shark Week programming. Today we review last night's "Killer Sharks."
Last night’s Shark Week episode, “Killer Sharks,” tells the tale of Black December, the label South Africans gave to the period from December 1957 through April 1958 because of the rash of shark attacks that occurred near Durban.
Unlike the other episodes that have aired so far, this one takes place completely in the past, and so the entire episode consists of dramatic re-enactment with a few authentic clips interspersed where possible.
Seven deadly shark attacks happened in the area, and all the while Dr. Harris, a marine biologist, worked hard to get to the bottom of them. He discovered that it was not merely one rogue shark causing all the problems, but that there were hundreds of them in the area. But what was bringing them so close to the tourist beaches?
It just so happened that December 1957 marked the beginning of the perfect storm for shark attacks: whaling vessels offshore were attracting sharks to the area; rivers were flooding and washing livestock out to sea, introducing new food sources and making the water murky; and there were more tourists than ever in the water due to recent resort development.
In other words, this event was extremely unusual, and highly unlikely to occur again (in fact, it remains one of the worst in history, over 50 years later). The average number of fatal shark attacks per year worldwide is four, which is lower than the number that occurred in South Africa over the four month period in this episode.
What’s more, as Dr. Harris said in this episode, shark research was in its infancy in the 1950s, and we have come a long way since then in our understanding of these creatures and what environmental factors may trigger such behavioral changes.
Editor's note: Happy Shark Week! All week long we'll be re-capping some highlights from Shark Week programming. Today we review "Going Rogue" and "Summer of the Shark."
Would a shark ever “go rogue” and start mercilessly attacking humans? That’s the question that last night’s episode in the Shark Week lineup sought to answer. Ever since New England beachgoers were terrorized by a rogue shark in “Jaws,” it has been a common fear that sharks, particularly great whites, are ruthless, man-eating machines.
This episode shed some light on the matter with a mix of shark attack stories and scientific studies on shark behavior. The conclusions likely elicited a collective sigh of relief across America: Sharks have never in fact gone rogue like Jaws did, but instead almost always bite a human as a result of other environmental factors at play.
In reality, the likelihood of being attacked by a shark is extremely slim. So for all the readers out there who were wondering whether it was safe to go back in the water, consider the possibility of a shark going rogue to be out of the question.
Editor's note: Happy Shark Week! All week long we'll be re-capping some highlights from Shark Week programming, starting with today, and "Great White Invasion."
Great white sharks appear to be more common than ever nowadays, according to “Great White Invasion,” which aired last night as a part of Shark Week's first night of programming. The episode tracked these huge predators as they encroach on popular beaches from Australia to South Africa to southern California.
Why they are coming closer to shore is not completely understood, but scientists point to the availability of fish as well as the opportunity for sharks to sunbathe and enjoy higher oxygen levels in shallower waters as possible explanations. And even though the number of annual shark attacks worldwide has risen in recent years, it is still extremely low compared to the number of beachgoers.
So are great whites really “invading” our coastlines? Not quite. In fact, according to the Census for Marine Life, scientists estimate that there are only about 3,500 great white sharks left in the entire world. Of these, an estimated 219 live off the central California coast, so in reality, sharks aren’t exactly swarming in our oceans just yet.