In this last installment of our Animal Myths series, we’ll be diving in to tackle misconceptions about the wet and wild critters that live underwater!
1. Sharks are man-eaters
This first, pervasive misconception taps into some basic human fears. We rarely face predators large and strong enough to pose a threat to us, so when we are confronted by a creature that could cause us harm, we fear them greatly. Of course, the propagation of this myth has been helped by feature films such as Jaws and The Meg, which have statistically altered the public perception of sharks. In truth, most sharks aren’t large enough to pose a serious threat to humans; a majority of the world’s 500+ species of sharks are smaller than a meter (3 feet) in length. What’s more, the largest species (whale, basking, and megamouth sharks) actually feed on plankton. Additionally, shark attacks are exceptionally rare – only about 80 “unprovoked” shark attacks are reported worldwide each year, of which 1-4 are fatal . You are FAR more likely to be struck by lightning (~240,000 strikes/year, 6,000 fatal ) or killed by a cow (~20 deaths/year ). Great white sharks – the sharks featured in Jaws – are perhaps the most persecuted by this myth, and not without reason; these sharks are truly apex predators and can reach over 20 feet in length. But even then, they are responsible for <10 attacks on humans per year (read more about great whites in this Creature Feature). In contrast, the megalodon – the infamously large shark at the focus of The Meg – is not only extinct but has actually been so for longer than previously thought !
2. Sharks must constantly swim to survive
While it is true that some sharks need to be in nearly constant motion to move water over their gills, many sharks do not. Instead, there are two breathing mechanisms commonly found in sharks. The first, ram ventilation, uses the momentum of swimming to actively push water through the shark’s gills . The second, buccal pumping, is driven by a structure called a spiracle – an opening behind the eye that actively pumps water across the sharks’ gills . Many sharks actually switch between these two mechanisms, utilizing ram ventilation when they’re on the move and buccal pumping when they come to a rest. Some sharks, including great white and whale sharks, are obligate ram ventilators – they do not have spiracles to assist their breathing – and must maintain nearly constant motion. However, even these active sharks have been observed basking, seemingly still, but how they maintain high enough oxygen levels during this time is as-of-yet unknown! Furthermore, sharks lack a swim bladder (a gas-filled organ possessed by some fish that provides a consistent buoyancy) and they will sink to the ocean floor if they stop moving. Thus, though sharks have a myriad of adaptations that allow them to handle changes in depth (and the corresponding changes in pressure), most species must actively swim in order to move up and down the water column .
3. Frogs will sit in boiling water if it’s heated slowly
This myth is a classic tale adored by politicians everywhere. The fable goes: if you drop a frog into boiling water, it will immediately jump out but, if the frog is put in tepid water that is then brought slowly to a boil, the frog will stay put until its death. Politically, this story is used to warn about slowly encroaching threats (as in this recent article about climate change). The origin of this myth is equally as fascinating as its content. This tale originated in the 19th century, while physiologists were conducting experiments to determine the location of the soul. This process, apparently, involved quite a bit of frog boiling . Interestingly, one of these experiments did find that a frog will stay still if water is boiled slowly around them…if the frog had first been lobotomized. Ultimately, this myth is false on two fronts. As Dr. Zug (curator of reptiles at the Museum of Natural History) said, “if a frog had a means of getting out [of boiling water], it certainly would.” Additionally, most frogs won’t jump out if you drop them into already boiling water – they’re more likely to be killed by the process !
4. Goldfish have a 3-second memory span
If you’ve ever owned a goldfish, you’ve probably heard this myth. The origin of this myth is harder to pinpoint but likely began as a way for humans to justify keeping goldfish in small, uninteresting enclosures (by the way, goldfish create a lot of waste and typically need more space than most fish). Research conducted at the Israeli Technion Institute of Technology demonstrated that fish trained in captivity and then released into the wild still responded to their training cue five months after being released . This study teaches us that fish memories are more likely on the scale of months or years than seconds. Interestingly, a series of studies in the ’60s used different chemical agents to disrupt goldfish memory formation; these studies relied on a goldfish’s ability to remember training exercises for bouts of 20 to 40 minutes across different days . So, even though the exact memory span of goldfish has not been measured, it’s safe to assume it is far, far longer than a few seconds.
5. Goldfish will only grow as big as their container
Another common misconception about goldfish is that they will only grow as large as their container. While not strictly false, this fact should come with a disclaimer. More accurately: if goldfish are kept in too-small containers, their growth will be stunted. Actually, goldfish are some of the largest and longest-lived commercial fish; they regularly reach over a foot in length and can live upwards of 20 years! Keeping goldfish in bowls can impede fish growth in a myriad of ways; bowls are too small, which can lead to muscle atrophy, and lack proper filtration, which can cause toxic levels of waste buildup . Additionally, some goldfish naturally produce a growth-inhibitory hormone to reduce competition but, when trapped in a small tank, this hormone often ends up being self-inhibiting ! Without appropriate space and filtration, goldfish are likely to live a far shorter life. For more information about determining the proper size tank for your fish, check out this article.
6. Orcas are “killer whales”
While orcas are in no doubt apex predators, the moniker “killer whale” is a bit of a misnomer. First off, orcas are not whales – they actually belong to the dolphin family! Secondly, the term “killer whale” may actually be a mistranslation of “killer of whales,” as orcas have been known to hunt and kill whales . Orcas, like many dolphins, hunt in large groups called pods. Dolphin species utilize a wide variety of cooperative hunting strategies; often, individual groups will specialize on a certain hunting style and prey type. In general, dolphins, including orcas, are voracious, successful predators . So what sets orcas apart from the rest of the dolphins as “killers”? Perhaps their size. As the largest members of the dolphin family, orcas are able to hunt a wider variety of species including seals, other dolphins, the aforementioned whales, and even some sharks .
Ryane Logsdon in a member of the Animal Behavior Graduate Group. Her Ph.D. research aims to understand the influences of social and structural environments on courtship behavior in the Greater sage-grouse.