This week we are discussing some marine mammals that live in the extreme. Now this may be because they live in rivers, or have giant tusks, or they are just GIANT! We discuss what makes these species so unique and so extreme in nature. These are some pretty impressive adaptions for some unique habitats and ways of living, read on to learn more.
Walrus – Tusks
Within the pinnipeds, the walrus is the only remaining extant species of the family Odobenidae, a previously speciated family. One of the few odobenids to actually have tusks and the only extant pinniped to have such, these elongated canines exhibit multiple features key to the survival and livelihood of the walrus. Weighing up to 12 pounds and as long as 3.25 feet each in the males, the tusks are commonly used for sexual display and sparring amongst the males. Males with larger tusks tend to dominate social groups, therefore mating with the most females. As opposed to other tusked animals being found in just one sex, walrus tusks are found in both males and females, both utilizing them for other tasks.
The main line of defense of the walrus (outside their sheer size and thick skin/blubber) is their tusks, using them to fight off rare attacks of polar bears or killer whales and other threatening walruses. The tusks are used as tools as well, whether it be for hauling their bodies back on to ice flow (hence their Latin name Odobenus rosmarus, or “tooth walking sea horse”) or helping chip holes in the ice to breathe or enter the water. They also may use their tusks to stir up sediment on the seafloor to help reveal mollusks, their primary food source. Though the few extinct Odobenids that had tusks were thought to use them to crush open mollusk shells, the walrus does not use them for this purpose at all, rather they use their specialized lips and “piston tongue” to create a vacuum and suck the meat out of the shells.
River Dolphins – Habitat
Without doubt river dolphins are pretty extreme – they are the only cetaceans that live 100% of their lives in freshwater! This might seem strange, but because they are mammals like all whales, dolphins and porpoises, as long as they can breathe air it doesn’t matter if they live in fresh or saltwater. It is thought that the river dolphins are actually one of the most ancient forms of dolphin, ones that simply never made it all the way out to the ocean or got stuck in rivers due to changes in geological landscapes.
There are 6 extant (aka living) species of river dolphin and 1 species of river-dwelling porpoise (the Yangtze finless porpoise). They are found in larger river basins of South America and Asia (such as the Amazon and the Ganges), however most of the river dolphins are restricted to very small sections for river for much of the year. Only when the wet season arrives do they have enough water to swim farther into the river systems, which often means rainy season is the time to socialize!
Because they live in rivers, which are often shallow, river dolphins have a unique adaptation to allow them to navigate amongst root and tree limbs that descend into the water: their neck vertebrae are not fused like in other cetaceans, which allows river dolphins to turn their heads up to 90 degrees! This increased maneuverability may make the difference between catching prey or not, or being able to navigate in particularly debris-laden parts of a river versus getting stuck.
One of the most well known river dolphins is the Amazon river dolphin, and you might have heard about it because the males are, well, pink. That’s right: pink. This color is thought to result from a buildup of scar tissue (which means older males are a more vibrant shade of pink), and is apparently very attractive to females.
The main threat to river dolphins is, unfortunately, us. Overfishing, entanglement in fishing gear, pollution of rivers, and dam building are all major causes of harm to river dolphins, and are likely the cumulative cause of the Yangtze river dolphin (also known as the Baiji) being declared functionally extinct in 2006. Functionally extinct means that even if some animals remain alive in the wild, they are so few in number that we cannot find them, and they will likely not be able to repopulate quick enough to prevent them going extinct completely. There was one potential sighting of a baiji in 2016, however this was not able to be confirmed so they have remained listed as functionally extinct.
Blue Whales – Size
We have discussed some pretty neat extremes of the marine mammal world, but let’s talk about the elephant, or should I say elephants, in the room: the blue whale. The sheer size of a blue whale is hard to comprehend, they can be as long as 3 school buses (up to 100ish feet), their tongue can weigh as much as an elephant, their heart is as big as a small car (an adult human could crawl through the arteries) and they can weigh up to about 30 elephants (up to 200 tons). They are the biggest animal that has ever lived. Ever. That’s right, even dinosaur don’t measure up.
But that isn’t where the extremes end. The calves are born as one of the biggest animals already at 3 tons and 25 ft. Blue whales are one of the longest live, one was found to be 110 years old. They used earplugs to measure the age – imagine the size of that, now that is a lot of wax! They are also one of the loudest animals on the planet. It is thought that they can hear each other up to 1000 miles away, and they can reach 188 decibels (a jet engine is only 140 decibels). Don’t be next a blue whale that starts to call!
One of the weirdest things about these giants is that they feed almost exclusively on krill, small shrimplike crustaceans, one of the smallest animals. Imagine how much a blue whale would have to eat…ok I won’t make you imagine – and adult can eat 4-6 tons of krill per day! They do this by having a big mouth… literally. Having a mouth/body that is specialized for catching swarming krill, means the larger the mouth the more you get, and thus this is what researchers think made the blue whales evolve to such a large size – check out an article about it here (https://www.annualreviews.org/doi/abs/10.1146/annurev-marine-122414-033905?journalCode=marine).
But the downside is that if you specialize and something happens to that prey source, the predator has nothing to fall back on, no other prey to substitute, and that can negatively affect their survival. Speaking of which, they were hunted during the whaling era and have not recovered like some other of the large whale species. You would think that finding a 100 ft, 180 ton animal would be easy, but even though they are huge, they are hard to find and observe, living in open ocean waters. Thus we know little about their movements and life history. An important reminder that large size does not mean large visibility, and that we need to know more about the blue whale in order to protect it.