Otterly unbelievable!

So I realized the other day that I've named this blog "thought you otter know" and its been 12 posts so far with no otters! [Except for this brief mention during the tool usage post] Well today that all changes. Today I'm going to attempt to convince you that otters are possibly the greatest animals on the planet.

Baby sea otter held at the Monterey Bay Aquarium

after being found orphaned on the beach.

And done.

Just kidding. As adorable and amazing as that was there is so much more to these furry balls of walking "awws". So here are some general facts about otters followed by one or two of my favorite species.

There are 13 extant species of otters found in various corners of the globe in a variety of habitats from the semi-aquatic to the fully marine. They range in size from the relatively tiny, Oriental small clawed otter (Amblonyx cinerea) to the absolutely massive, by otter standards, giant river otter (Pteronura brasiliensis).

Left: Oriental small clawed otter (Amblonyx cinerea). The smallest of the otter species it grows to between 70-100 cm of which approximately 1/3 is its tail.
Right: Giant river otter (Pteronura brasiliensis). The largest of the otters, at least by length, they can grow up to 1.7 m long (over 5 1/2 feet).

All otter species are members of the subfamily Lutrinae within the family Mustelidae which contains all weasel species and their relatives.

Various Mustelidae (Clockwise from left): American marten, ferret, wolverine, "Pepper" (otter), honey badger

A group of otters is referred to variously as a bevy, family, lodge, romp, or when in the water a raft. All species are amphibious to some degree and so fish is a staple of the otter diet for the most part, although some species supplement this with frogs, crabs, shellfish, or small mammals and birds.

Sea otter using a rock to smash open clams.

Sea Otter, Enhydra lutris

Sea otters are the "odd man out" of the Lutrinae family. Not only are they the heaviest otter species, and in fact the heaviest of all the weasel family. They are also the only otter capable of living their entire lives without leaving the water. Found along the Pacific coasts of North America and Asia these otters are renowned for their pelts. They have the densest fur of any animal, with approximately 150,000/cm squared (~1,000,000 per square inch). In comparison chinchillas, with the densest fur of any terrestrial animal, have on average 24,000/cm squared (~155,000 per square inch). While their incredibly thick fur may help protect sea otters from the cold of the Pacific it also nearly led to their extinction with poachers drastically reducing their numbers during the 18 and 19th centuries. When the Treaty for the Preservation and Protection of Fur Seals (which included a moratorium on sea otter harvesting) was signed in 1911 by Russia, Japan, Great Britain on behalf of Canada, and the US population estimates ranged from only 1,000-2,000 individuals. Since then they have rebounded to ~125,000 individuals worldwide (as of 2012), but they are still listed as Endangered by the IUCN Red List.

Sea otters are a classic example of a keystone species. This means that their removal from an environment or ecosystem would have a much greater impact than their size and numbers would suggest. For example, kelp forests are prime marine real estate. They provide a 3-dimensional environment for organisms to live in, hide from predators, feed on, etc. These forests are anchored to the sea floor by the kelp's holdfast (like the roots of a tree), and these holdfasts are food for many benthic organisms such as sea urchins. While there are sea otters present they regulate the urchin population, however, if you remove the sea otters the urchin population explodes. This leads to the destruction of the kelp forest as the urchins destroy the holdfasts quicker than new kelp can settle and grow. Therefore without sea otters the entire ecosystem is destroyed as shown in this video from the PEW Charitable Trusts:

The importance of sea otters.

European Otter, Lutra lutra

The European otter, also known as the Eurasian otter or the Old World otter, has the widest range of all the otter species. They span three continents (Europe, Africa, Asia) from Ireland to China, and as far north as Scandinavia down to North Africa and South-East Asia. This species mainly lives in freshwater, but can be found along the coast although they require freshwater regularly to clean their coats. These otters are also highly territorial along sex lines, meaning that male-female territories may overlap, but never male-male or female-female.

Giant River Otter, Pteronura brasiliensis

As mentioned earlier giant river otters, as their name suggests, are the largest of the otters and in fact the largest of any Mustelidae (in terms of length, as mentioned sea otters are the heaviest). They are also strongly social species, with family groups ranging from 2-20 individuals held together by a main breeding pair. Their social ties allow them to work and hunt together successfully. They are known as ariranha in Brazil which translates to water jaguar, and in Spanish they are lobo del rio, or river wolves. The comparisons suggested by these names are well earned as this video shows:

Clip from BBC 2 documentary showing a family of giant

river otters attacking and dispatching a caiman.

These otters are apex predators, which is no easy task in the Amazon. Their diet consists mainly of fish including catfish and piranhas, but they have also been known to take down caimans and anacondas! When full grown these otters have no serious natural predators (although occasional predation by jaguars, and anacondas has been suggested, but never observed) and so their greatest threats come from humans (what a shock). They are poached for their fur, and are threatened by habitat destruction. The IUCN Red List classifies them as Endangered due to the threats facing them which are compounded by the difficulties to recover and re-colonization (they are a slow growing, late breeding species).


Well I think that's probably enough otter talk for one day. I will leave you with a couple cute videos of otters (the last one I took myself at an otter sanctuary near Plymouth in the UK).

Sources

A craftsman is only as good as his tools

Clip from Hitchhiker's Guide to the Galaxy tv series.

Words of wisdom from the late, great Douglas Adams. One of the identifiers, and markers of intelligence in a species is the use of tools. For a long time humanity assumed that it was the sole species to possess this trait. However, the creation and use of tools is a trait that has been documented in numerous species throughout the years. Here we shall discuss as many of them as I feel like typing about.

1. Primates

Ok this one is a bit of a cheat because so many of our closest genetic relatives have displayed a talent for tool creation and usage. So I'm going to briefly touch on several species of primates in no particular order.

First off is the most obvious, Chimpanzees (Pan troglodytes). Chimps are one of our closest genetic relatives, along with Bonobos (Pan paniscus), sharing approximately 98.7% of our genetic code.

From Left: Chimpanzees, Human, Bonobos. Johnny Depp is 98.7% genetically identical to the animals on either side of him.

Chimps and bonobos have been documented crafting and using tools in the wild, but both species have a much higher tool usage rate when held in captivity. Tool usage in these species is widely varied with tools being developed to hunt, scavenge, collect honey and water, crush and chop fruits, nuts and vegetables, and for personal grooming.

Chimps using tools to fish out insects.

Another great ape species which utilizes branches and leaves as a remarkable variety of tools for a multitude of jobs is the Orangutan (Pongo pygmaeus and Pongo abelii). Orangutans have been observed to use tools for many functions similar to chimps and bonobos. They craft hunting and gathering tools, use leaves as gloves to grab thorny branches, and use leaves as napkins. They have even been shown to utilize leaves as megaphones, possibly to make themselves seem larger and more threatening to predators. However, they have also shown a trait that you might think is a uniquely human idea. They have been observed using tools to masturbate. Yeah you read that right. Orangutans fashion tools to help them "get off", and it's been seen in both male and female orangs. While this is certainly the most eye grabbing trait, orangs have also shown a remarkable ability to "ape" (hehehe) human tool use. In the wild orangutans have been observed copying humans spear fishing, and in captivity they have been taught to craft stone hand axes.

Orangutan attempting to spear fish.

Finally among the non-ape primate species the most notable are the capuchin monkeys. Capuchins are part of the new-world monkey subfamily Cebinae, and are split into two genuses, Cebus and Sapajus. Capuchins of both genus have shown a remarkable propensity towards stone tool use. They have been documented using a stone "hammer and anvil" to crush and crack open nuts, fruits and even oysters. However, this is not some innate ability of these monkeys. It can take up to 8 years for Capuchins to master the skills required to use these tools.

Clip from BBC Earth documentary showing Capuchin monkeys cracking

nuts. Narrated by the brilliant Sir David Attenborough.

Capuchins have also shown ingenuity by using stone tools to dig up roots and tubers, and "milking" the secretions of certain arthropods to use as insecticides.

2. Elephants

There are three extant species of elephant, the Asian elephant (Elephas maximus), African bush elephant (Loxodonta africana), and African forest elephants (Loxodonta cyclotis). While these species are famed for their "infallible" memories and are considered among the most intelligent species on the planet, they are not often thought of as tool users. They make up for their lack of opposable digits through the use of their incredibly dexterous trunks. Elephants have been seen choosing, stripping and shaping sticks and branches for a variety of purposes. They create fly swatters, back scratchers, and toe cleaners. They have also shown foresight in their tool creation. Elephants have been observed digging holes which fill with water, then filling the hole with a wad of chewed bark to absorb the water, and covering the hole over with sand to prevent evaporation. This creates a cache of water for the elephant should it return later and need a drink. Elephants have also shown the ingenuity to use large rocks to crush electric fences, either shorting them out or breaking a hole for the elephant to walk through. In captivity Asian elephants will also use boxes in their enclosure as stepping stones to reach food placed purposefully out of reach.

Elephant chews stick to create tool for scratching.

3. Sea Otters!

I had to include this one. As you may have noticed from the background and the title of my blog I have a weak spot for otters. Now tool use is fairly uncommon in the animal kingdom, while it may not appear so from this blog so far, but it is even more unusual in the marine environment. Sea otters (Enhydra lutris) however, are one of the few species with documented tool use capabilities.

Sea Otter using rock on its belly to smash its prey.

I'm sure we're all familiar with the images and videos of sea otters holding the clam, or urchin on their belly and smashing it with a rock to open it. It turns out that sea otters also use rocks to remove their food from the sea bed and rocks it clings to. Otters hunting abalone (a type of marine snail) will often use rocks to bash the snail in an attempt to prize it from the rocks it is attached too. This is much harder than it sounds as the snails can grip the rock with a force equal to 4,000x its own body weight!

Once the otter has prized the snail from the rock (usually requiring several dives to achieve this) it must then break through the snail's hard shell. Recently a researcher from Monterey Bay Aquarium, Jessica Fujii, reported that her team had found that the rate of tool use in otters varies by location. Sea otters down south, off the California coast showed a much higher rate of tool use than those observed in Alaskan waters. Fujii said that this is due to the dominant prey species for these different populations of otters. While urchins are spiny and tough looking, they are actually much easier to break open than the abalone that otters hunt further south. This explains why Alaskan otters showed tool use while eating ~1% of the time compared with the ~16% usage rate by southern otters.

Sea otter using rock to smash open clams.

4. Dolphins

Finally we have come full circle. Here we find the species many consider to be the second most intelligent on the planet, the bottlenose dolphin (Tursiops truncatus). Dolphins are similar to elephants in that while the intelligence is much lauded, they are not considered prime examples of tool using species. However, dolphins have been observed using sponges to protect their rostrum as they hunt for fish along the sea floor. Genetic studies performed on dolphins in Shark Bay, Australia (where this behaviour has been documented) show that it stems from a single matriline (female lineage) with mother's apparently teaching the skill to their daughters. There are also reports of dolphins in this area using conch shells to scoop prey off the bottom making them easier for the dolphins to eat. Dolphins have, like Orangutans, also been documented masturbating in the wild. While perhaps not technically "tool use" a video does exist showing a river dolphin "using" a headless fish.

Bottlenose dolphins in Shark Bay using sponges to protect them while hunting.

Well that's all I have for this blog, thanks for checking it out. I hope you enjoyed the pictures and videos. Come back again soon, and check me out on The Imposter Podcast, run by a good friend of mine, Amir Fogel. Anyway thanks for stopping by!

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