Last week, Animal Planet aired a fictional mockumentary about mermaids. From an educational perspective, it was a disaster that was rightfully described as “the rotting carcass of science television” by Brian Switek. As Dr. M on Deep Sea News pointed out, one of the troubling results of this TV special was the discovery that some people believe that mermaids are real.

When I pointed out on Facebook and twitter that mermaids do not exist and that I hoped none of my friends believe otherwise, it inspired a long and interesting discussion. Someone asked why it matters if people believe in mermaids, as they felt that a sense of whimsy among the public is a good thing. Someone pointed out that scientists are discovering amazing new species all the time. More than a few people said “anything is possible.”

Sure, scientists discover new species all the time, but while finding a new species of monkey, orchid, or jellyfish can be interesting, it is not proof that “anything is possible” and it is not the same thing as finding a species of talking, thinking humanoids with fish tails on the lower half of their bodies.  There’s a big and important difference between enjoying fantasy novels and wishing that certain fantastical creatures exist (i.e. having a sense of whimsy) and genuinely believing that those creatures really do exist.

These people don’t believe that in the vast and unexplored ocean, there may be some bizarre undiscovered species still out there. They believe that talking, thinking humanoids with fish tails on the lower half of their bodies exist and are acknowledged as existing by the scientific community. This displays a troubling lack of awareness of reality that likely is not limited to a belief in mermaids. For the benefit of those who have paid so little attention to what’s going on in the real world that they believe mermaids exist, here are five other things that you should, but likely do not, know about the oceans.

The oceans are not inexhaustible, we’re currently overharvesting many resources, and the consequences can be disastrous. This was first brought to the attention of the public on a large scale in 1992 when the Canadian government declared a moratorium on the cod fishery. For centuries, cod stocks were considered to be inexhaustible and were a major reason for the European colonization of large parts of North America. Fishermen took too many cod, not enough were left to replenish the population, and a potentially renewable resource so critical for the food supply, culture, and economy of Canada was gone. Tens of thousands of people were unemployed overnight and an entire province of a developed country suffered major economic problems for many years because one fish stock was overexploited.

World leaders didn’t learn their lesson, and overfishing continues to this day on a larger scale. Worldwide, 32% of all fisheries are “overexploited, depleted, or recovering”, and almost 50% are “fully exploited”, according to the U.N.’s Food and Agriculture organization.    The United States has one of the world’s best fisheries management plans, and we’re still in trouble- according to the National Marine Fisheries Service 2011 report , 21% of U.S. fish stocks are overfished (their populations are below a critical threshold) and 14% of U.S. fish stocks are experiencing overfishing (too many fish are being removed from the population, which can result in being overfished if it continues).  This isn’t just an environmental problem. According to the FAO, fish provides at least 15% of the protein intake for more than 3 billion people (including some of the poorest people on the planet), and the global fishing industry is worth almost $100 billion annually and employs millions of people . While some recommend avoiding seafood entirely, I recommend instead eating sustainable seafood with a minimal environmental impact.

Current fishing practices aren’t just problematic for the fish species we are trying to catch. Commercial fishing typically doesn’t use the rod and reel that recreational fishermen are used to. A single longline can be many miles long and have tens of thousands of hooks. A purse seine net can be several miles across, and a trawl net can fit half a dozen 747s in its wide opening. With gear like this, bycatch (catching not just the target fish, but also other animals that happen to be near that fish) is perhaps inevitable, but few are aware of how serious the problem is. For many fisheries, the bycatch is more than the target catch, and in some, less than 10% of the total weight of the catch is target. Much of the bycatch, which includes sea turtles and sea birds in addition to non-target fish, is just dumped overboard, and it usually dies. The FAO estimates that 7 million tons of bycatch is discarded every year.

Additionally, some types of fishing damage the marine environment itself. For fisheries like “dynamite fishing” or “cyanide fishing“, which typically take place on fragile coral reefs, it’s probably pretty clear how problems can arise. Other larger-scale fishing techniques, like trawling, can destroy important habitats by dragging a heavy weighted net over the bottom. This is equivalent to hunting for deer by knocking down all the trees in the forest that had taken years to grow, and also killing everything that used to live there. These trawl scars on the sediment are so bad that they are sometime visible from space. Relatively simple solutions often exist for minimizing bycatch, and it can be easy to support fisheries that have relatively low bycatch.

What you do affects the ocean, even if you live far away. When you don’t dispose of garbage properly, it often ends up in the ocean. In particular, there’s an alarming amount of plastic in the ocean, including a place called “the great Pacific garbage patch” (a huge area full of tiny pieces of plastic waste). Plastic bags resemble jellyfish, and sea turtles often die when they eat them by mistake. Using resuable shopping bags and disposing of your trash properly can minimize these problems.

Untreated or poorly treated sewage is dumped into the ocean all over the world, which can spread disease. Even relatively good waste treatment plants aren’t great at removing the pharmaceuticals which are excreted as waste after we take medicines. Birth control hormones can be especially harmful to the marine environment, and are already affecting the reproductive biology and habits of numerous species of fish and invertebrates that have been exposed.

Even human activities that occur a thousand miles from the ocean can affect what happens there. The best example of this is the Gulf of Mexico dead zone, a large area near the mouth of the Mississippi river with oxygen levels so low that most animals die. While a small dead zone may occur naturally, the process is greatly increased by waste and fertilizer runoff from farms all along the Mississippi.

Just because a fish is from “the ocean” doesn’t mean you should release it at the nearest body of saltwater. Invasive species are a relatively recent (but nonetheless serious) ecological problem that occurs when a non-native species is introduced to a region. Sometimes that introduction is accidental, but sometimes it occurs when someone buys a fish for an aquarium and releases it when it gets too big for their tank… even though the animal is not native to the local ecosystem. Occasionally that species has no predators in the new area to control it’s population growth.

One of the most serious marine invasive species is the lionfish, which are native to the Indo-Pacific but are now found throughout the U.S. eastern seaboard. They are popular aquarium fishes, and were believed to have been introduced to the Atlantic when aquarium owners released them. These voracious predators are outcompeting or eating native fishes, and their venomous spines deter predation. A single female can release up to two million eggs in a year. Because of this, invasive lionfish are found in densities much, much, much higher than what naturally occurs in their native range. Controlling invasive species such as lionfish is estimated to cost the U.S. economy well over $100 billion a year. As with many ecological problems, prevention is easier than cleanup- just don’t release your exotic pets and aquarium fishes!

Sharks aren’t a threat to you, they’re important, and they’re in trouble. What little people know about my study organisms is limited to what they learn from “Jaws” and overblown shark attack reports on the evening news. In reality, the majority of species of sharks have never hurt a human, and shark attacks from the few species which can be dangerous are extremely rare. The average American has a 1 in 5 chance of dying from heart disease in their lifetime, and a 1 in 3,800,000 (3.8 million) chance of being killed by a shark. Many sharks are the top predators of their ecosystems, which means they are important to the health of that ecosystem. Declines in shark populations have been blamed for the collapse of unrelated fisheries and habitats around the world as the food chain unravels. These shark population declines are very serious- about 16% of all shark, skate, ray, and chimaera species (and 1/3 of all open ocean shark species) are listed by the IUCN Shark Specialist Group as Vulnerable, Endangered, or Critically Endangered. There have been documented population declines of 90% or more in the last few decades in regions where sharks were once abundant. There are differences of opinion on how best to help sharks, but personally, I support a global well-managed shark fishery and do not support laws like “fin bans” (as described here).

Although mermaids don’t exist, the ocean is still full of wonders- and it needs your help. Please share what you learned here, and add other information you think people need to know about the oceans in the comments section. If we all share this with everyone we know, and they all share it with everyone they know, we may be able to reach 0.1% of the people that Khloe Kardashian reached when she tweeted about her belief in mermaids.