Sturgeons

[00:00:00] Alex Re: Hello, welcome to On Wildlife. I'm your host, Alex Re. On this podcast, we bring the wild to you. We take you on a journey into the life of a different animal every week. And I guarantee you, you're going to come out of here knowing more about your favorite animal than you did before. Today, we're taking a trip back in time.

[00:00:21] But we won't be needing a time machine. These modern day dinosaurs are still flapping their fins all these millions of years later. Carrying some serious armor and unique adaptations, it's no wonder these animals are still around today. So join me as we dive down to the ocean floor to take a swim with dinosaurs.

[00:00:42] Sturgeons

[00:01:00] are fish belonging to the Acapenseridae family, and there are around 28 species throughout the world. They're found only in the Northern Hemisphere, and they're some of the oldest fish on Earth. Their earliest fossils date back to the Middle Jurassic Period, which was over 160 million years ago. The only other living relatives in this family are paddlefish.

[00:01:26] They have an elongated rostra, which looks like a really long nose, that's filled with electroreceptors, much like the snout of the sturgeon. And we'll get to what those electroreceptors do later on in the episode. And just like the sturgeon, paddlefish are also considered to be ancient or primitive fish.

[00:01:45] When you look at a sturgeon, there are a lot of really cool characteristics. But the first thing you'll notice might be their size. For the most part, they can reach up to 16 feet long, although there have been larger ones. That 16 feet is also the same length of the average great white shark. The largest species of sturgeon is the beluga sturgeon.

[00:02:09] And the largest individual on record for this species was 23 feet long. And they really do look like prehistoric animals. Depending on the species, their coloration varies, but for the most part, they're either gray or like a tannish color. They also have bony, diamond shaped scales called scutes that run along their back, and these scutes can be extremely sharp.

[00:02:36] There are around two to six rows of them, and they're used for protection against predators. They have one dorsal fin on top of their body near their tail, and their tail fin is heterocircle. This means that the tail's upper lobe is longer than the lower lobe. They also have three sets of fins on their underside called the pectoral, pelvic, and anal fins that help with their movement through the water.

[00:03:04] Another characteristic that helps them while swimming is their swim bladder. The swim bladder is a gas filled organ that controls buoyancy, and it's located in the dorsal section of the fish. The walls of the bladder contract or expand depending on the ambient pressure. In other words, it changes to account for the depth that the fish is swimming at.

[00:03:27] Sturgeon skeletons are mostly cartilaginous, which is similar to sharks and rays. Cartilage is less dense than bone, which allows fish with this kind of body structure to move more easily in the water without expending excess energy. It also allows for more flexibility, which means more escapability from predators.

[00:03:49] You may think that this is another primitive characteristic of these ancient looking fish, but this is a derived characteristic, meaning it was passed on from the most recent ancestor. Older ancestors of sturgeons had fully bony skeletons. Also, aside from their scutes, they don't have scales. Their skin is more smooth and apparently feels like sandpaper.

[00:04:13] However, despite all of their shark like traits, they do possess few true bones, making them classified as a bony fish, whereas a shark doesn't have any bones. Cartilaginous fish, like sharks, also don't have a swim bladder, which is another characteristic that separates them from sturgeons. Lake sturgeons are a species that you'd find in the Great Lakes in the United States.

[00:04:39] Some individuals of this species can get to be over a hundred years old. And the really unique thing about sturgeons is that they can live in both freshwater and saltwater environments. This is something that most other fish can't do. Salmon being one of the only other exceptions. Most are Andromedas, migrating from saltwater to freshwater to breed.

[00:05:04] Traveling from saltwater to freshwater and vice versa requires something called osmoregulation. This is the control of salt and water concentrations in the body. A freshwater fish that isn't acclimated to saltwater won't survive in the ocean, because the water in their cells will leave And the cells will shrivel up, but sturgeons have multiple mechanisms in their body to counteract this, like the use of sodium, potassium, and cortisol.

[00:05:35] So sturgeons are really cool fish, but it doesn't stop there. They have some more really interesting adaptations and behaviors that we'll talk about right after the break.

[00:05:56] On this episode, I want to give a shout out to Kayla from Pennsylvania. Her favorite animal is a red panda. Did you know that red pandas can eat 30 percent of their body weight per day of bamboo?

[00:06:14] Now back to the episode. Now, what do sturgeons eat? Well, much like the whale shark, they eat surprisingly small things for their size. You'll find them mostly eating invertebrates and other small organisms like crabs. They are bottom feeders and scavengers, also known as benthic feeders. This refers to the benthic area of the ecosystem, which is like the floor of the body of water that they're in.

[00:06:42] Sturgeon's size may be misleading when it comes to their diet, but their mouth tells us the real story. Most importantly, they have no teeth, so everything that they consume is eaten whole and sucked in through their mouth. This is why they mostly eat small animals. Some species hunt fish in their older age, but they have to be small enough to be sucked into their mouths whole.

[00:07:07] Their very muscular stomach crushes their prey into pieces so that it can be digested. To find their prey, they use their sensory barbels located on the underside of their nose, which the fish drags on the bottom to find food. These barbels kind of look like whiskers and catfish have them too because they're bottom feeders as well.

[00:07:30] Sturgeons also have sensory organs called Ampullae of Lorenzini. This organ is located in the sturgeon's head and helps sense electromagnetic fields given off by other animals. Every animal gives off a small amount of electricity, and this organ can pick up on that. If you've listened to some of our other episodes, you may have heard of these weird organs, because sharks have them too.

[00:07:58] This ability to sense electricity makes up for their poor eyesight, but it makes sense why they didn't evolve to have the best eyes. Because the benthic zone is on the bottom of a lake or ocean, it's often dark and murky, making eyes pretty useless. Because they're so long lived, sturgeons don't reach maturity until they're about 15 to 20 years old, and they don't reproduce every year.

[00:08:26] Depending on how old the female is, she could reproduce once every 3 to 6 years. They need a specific set of conditions met in order to breed, such as proper oxygenation, water flow, and temperature, shallow rock, And they also need the correct photo period, meaning the correct amount of daylight in a day.

[00:08:49] The photo period is also utilized by plants to determine when to start restricting their resources. To reproduce, females will release eggs into a flowing river, and the male will fertilize the eggs. Large females can release four million eggs at a time. But the likelihood of them all being fertilized is slim to none.

[00:09:14] Around twice a year, sturgeons will travel in loosely formed groups during migratory periods. And they can migrate really far distances. They're also seen to come together during winter feeding and summer fasting. Okay, let's take our last break, and when we get back, we'll talk about some other weird sturgeon behaviors, as well as why they're one of the most valuable fish for humans.

[00:09:53] Time for today's trivia question. Leatherback sea turtles are known to eat around 16, 000 calories of this animal every day. The answer is Jellyfish.

[00:10:19] Something really interesting about sturgeons is that they can leap entirely out of the water. But the exact reason for this behavior is unknown. Scientists do have some thoughts about the reasoning behind this, such as group communication, hunting airborne prey like flies and mosquitoes, courtship or mating displays, shedding of eggs during spawning, and getting rid of parasites or escaping predators.

[00:10:47] These are all just hypotheses, and nobody really knows why they do it. There have actually been instances where boaters were struck by these sturgeons. This can be extremely dangerous. Remember, they have really sharp scutes, so they warn people that are touring areas where sturgeons are native to be cautious.

[00:11:07] Sturgeons are extremely impactful animals, important in both their environment and for humans. First of all, they're a predator for multiple invasive species, including the zebra mussel. Zebra mussels are extremely damaging to their non native habitats. Secondly, sturgeons are known as living dinosaurs, and we can use them to find out more about what life was like millions of years ago.

[00:11:35] They're also an indicator species, so their presence tells us if the ecosystem is healthy or not. Being so long lived, they also give us the rare opportunity to observe how they, as a species, are affected by modern day issues over time. They can show us how changes in temperature, Water quality and human activity is impacting major bodies of water.

[00:12:00] Remember how I was saying that they need specific water temperatures in order to reproduce? Well, this is where climate change comes in to have a major impact. Increasing water temperatures are disrupting the natural life cycle of the sturgeon, which is decreasing the amount that they can reproduce.

[00:12:18] Sturgeons also have a huge economic impact on humans. They are the source of caviar. Caviar is raw sturgeon eggs, and the price can be up to 10, 000 per pound. The eggs are harvested from mature females right before spawning. In the late 1800s and early 1900s, sturgeon harvesting was out of control, and we saw a major decline in their populations.

[00:12:46] Even before this, humans have been a problem for them. In North America, during the period of colonization, Native American tribes used sturgeon as a food source. But once colonizers and commercial fishermen forcibly took the land, sturgeon were considered pests as they would tear and break out of their fishing nets.

[00:13:07] So they would kill the sturgeons in masses in order to attempt to prevent this damage. Thankfully, due to conservation efforts, harvesting from wild specimens is now illegal. Aqua farms are now used in order to feed the growing demand for caviar. Unfortunately, the majority of farms still use harvesting practices that result in the death of the female.

[00:13:31] On top of the caviar industry, the inner lining of their swim bladder is also used to create a gelatin like product called icing glass. This is used for clarifying alcohol and making glue and adhesives. According to the IUCN Red List, 17 out of the 28 species of sturgeon are critically endangered. The rest of the species are either classified as vulnerable or endangered.

[00:13:59] One of their relatives, the Chinese paddlefish, was determined to be completely extinct in 2019. And the Yangtze sturgeon, also native to China, was classified as extinct in the wild in the same year. Luckily, in certain parts of the world, sturgeon populations are increasing, showing us that conservation efforts are actually making a difference.

[00:14:22] That's why you should check out the World Sturgeon Conservation Society, the World Wildlife Fund, and And N O A A. Thank you so much for coming on this adventure with me as we explored the world of sturgeons, you can find the sources that we use for this podcast and links to organizations that we reference at on wildlife.

[00:14:44] org. You can also email us with any questions at on wildlife. podcast at gmail. com and you can follow us on Instagram at on underscore wildlife or on TikTok. At On Wildlife and don't forget to tune in next month for another awesome episode and that's On Wildlife

[00:15:09] You've been listening to On Wildlife with Alex Re. On Wildlife provides general educational information on various topics as a public service Which should not be construed as professional financial real estate tax or legal advice. These are our personal opinions only. Please refer to our full disclaimer policy on our website for full details.