---
title: "What the sources say about the Sea Otter | AnimalTracks.wiki"
description: "58 claims from the Sea Otter profile, each beside the words of the source that backs it."
image: "https://animaltracks.wiki/images/animals/sea-otter-1.webp"
canonical: "https://animaltracks.wiki/animals/sea-otter/sources/"
---

# What the sources say about the Sea Otter (*Enhydra lutris*)

> 58 claims from the Sea Otter profile, each beside the words of the source that backs it. A "..." marks a cut in a quote and [brackets] an insertion.

Profile: [Sea Otter](https://animaltracks.wiki/animals/sea-otter/)

## Sea Otter Species Profile. Alaska Department of Fish and Game.

https://www.adfg.alaska.gov/index.cfm?adfg=seaotter.main

| The page says | The source says |
| :--- | :--- |
| The densest fur of any mammal | Sea otters have the densest hair coat of any mammal, with 800,000 to one million hairs per square inch |
| a rock tucked under one arm | will use tools, such as rocks (which they store under their "arm pit" while diving), to crack open shells |
| Up to a million hairs per square inch, the densest fur of any mammal | Sea otters have the densest hair coat of any mammal, with 800,000 to one million hairs per square inch |
| a skin pocket that carries a rock for cracking shells | will use tools, such as rocks (which they store under their "arm pit" while diving), to crack open shells (note: The pocket is ADFG's own "Sea otters have a pouch in their armpit to store and carry food.") |
| Sea urchins, crabs, clams, mussels, octopus, other marine invertebrates and fish | Their main prey species include sea urchins, crabs, clams, mussels, octopus, fish, and other marine invertebrates. |
| in the North Pacific | Currently sea otters can be found in Alaska, Russia, British Columbia, Washington, and California. (note: Every place ADFG lists borders the North Pacific.) |
| the largest member of the weasel family | The sea otter is the largest member of the weasel family. |
| growing up to 5 feet (1.5 m) long | Adult sea otters may grow up to 5 feet in length. (note: 1.5 m is a conversion of the source's 5 feet.) |
| Males weigh 80 to 100 pounds (36 to 45 kg) and can weigh more | The males weigh 80-100 pounds but can weigh more than 100 pounds. (note: 36-45 kg is a conversion of the source's 80-100 pounds.) |
| females are smaller at 50 to 70 pounds (23 to 32 kg) | The females are smaller, weighing 50-70 pounds. (note: 23-32 kg is a conversion of the source's 50-70 pounds.) |
| It relies on a high metabolism and its plush coat instead | Sea otters rely on their high metabolism and their plush coat to keep warm. |
| The fur traps air, which provides 4 times as much insulation as the same thickness of fat would | which fluffs their fur and traps air. Their body heat warms the trapped air and further insulates them. The trapped air provides 4 times as much insulation as the same thickness of fat would provide. |
| A sea otter dives to the bottom to catch its prey | They dive to the bottom to catch their prey and surface to eat their food. |
| Its main prey include sea urchins, crabs, clams, mussels, octopus and fish | Their main prey species include sea urchins, crabs, clams, mussels, octopus, fish, and other marine invertebrates. |
| At the surface it rolls onto its back, sets the food on its chest, and may crack a shell open with a rock it stored under its "armpit" during the dive | Upon surfacing, the otter will roll onto its back and place the food on their chests. They eat using their front paws and will use tools, such as rocks (which they store under their "arm pit" while diving), to crack open shells. |
| Dives generally last one to two minutes, though an otter can hold its breath for more than five | The dives generally last 1-2 minutes, but they can hold their breath for over 5 minutes. |
| Russian explorers began the sea otter fur trade in the 1700s | Russian explorers began the sea otter fur trade in the 1700s. |
| the population rebounded dramatically in the 20th century | Following protection under the Fur Seal Treaty in 1911, the sea otter population rebounded dramatically in the 20th century. |
| It relies on a high metabolism and a plush coat instead | Sea otters rely on their high metabolism and their plush coat to keep warm. |
| A sea otter's fur, a dense underfur beneath longer guard hairs, has 800,000 to one million hairs per square inch, more than a human head holds in total | Their fur is made up of a dense underfur, ranging in color from brown to black, and longer guard hairs. ... 800,000 to one million hairs per square inch (humans only have 20,000 hairs on their whole head) |
| Grooming fluffs that fur and traps air, and the trapped air provides 4 times as much insulation as the same thickness of fat would | When sea otters are not foraging, you often see them grooming their fur. They do this to dry their fur and remove salt crystals and excess oil, which fluffs their fur and traps air. Their body heat warms the trapped air and further insulates them. The trapped air provides 4 times as much insulation as the same thickness of fat would provide. |
| To open its food | will use tools, such as rocks (which they store under their "arm pit" while diving), to crack open shells |
| an otter that floats on its back, sets its food on its chest and cracks shells open with a rock | Upon surfacing, the otter will roll onto its back and place the food on their chests. They eat using their front paws and will use tools, such as rocks (which they store under their "arm pit" while diving), to crack open shells. (note: vibe.reason, #384) |

## Sea otter. Oregon Zoo.

https://www.oregonzoo.org/animals/sea-otter

| The page says | The source says |
| :--- | :--- |
| Wild sea otters live between 15 and 20 years | Wild otters live between 15 and 20 years. |
| Unlike most marine mammals, which have thick layers of fat to keep warm | Unlike most marine mammals, which have thick layers of fat to help keep them warm, the sea otter doesn't. |
| a dense underfur that a top layer of long, waterproof guard hairs helps keep dry | A top layer of long, waterproof "guard hairs" helps keep its underfur layer dry. |
| The Densest Fur of Any Mammal | the densest fur of any mammal in the world |
| A sea otter's underfur has 1 million hairs per square inch, while a human head holds about 100,000 hairs in total | Its short underfur has 1 million hairs per square inch. By comparison, we only have about 100,000 hairs in total on our heads! |
| The otter grooms almost continuously, somersaulting, twisting and rubbing its fur to trap air bubbles against its skin | It grooms itself almost continuously, doing somersaults, twisting, turning and rubbing its fur. All this activity traps air bubbles against its skin |
| Its front paws find and grab it, while its whiskers feel the movement of prey animals in murky water | A foraging sea otter uses its front paws to find and capture prey underwater. Its whiskers help it to feel the movement of prey animals in murky water. |
| It tucks each catch into a pocket of loose skin under a foreleg and carries it up to eat | It tucks its prey into one of the pockets of loose skin on the bottom side of each of its forelegs and carries it to the surface to eat. |
| It usually feeds in water no deeper than 60 feet, but can dive to 300 feet or more if needed | A sea otter dives for food, usually in water no deeper than 60 feet, but it can hold its breath for 5 minutes and dive to 300 feet or more if needed. (note: Final pass: replaced ADFG's '5-250 feet' range, which the Oregon Zoo's current page contradicts.) |
| Its metabolism also runs at two to three times the rate of other mammals its size, so it needs to eat about a quarter of its own weight every day | Because its metabolism is 2-3 times the rate of other mammals its size, it needs to eat about 25% of its weight every day. |

## Enhydra lutris (sea otter). Animal Diversity Web, University of Michigan.

https://animaldiversity.org/accounts/Enhydra_lutris/

| The page says | The source says |
| :--- | :--- |
| a keystone predator that stops urchins from overgrazing kelp forests | They are considered a keystone species and play a major role in the community by controlling herbivorous invertebrates. Sea otters prey on sea urchins, thereby preventing sea urchins from overgrazing the kelp forest. |
| Kelp forests and shallow coastal waters over rocky or soft seafloor | Sea otters inhabit temperate coastal waters with rocky or soft sediment ocean bottom. They live in offshore forests of giant kelp (note: "Shallow" is ADW's "they prefer coastal waters up to 30 meters deep".) |
| a sea otter has no insulating fat at all | Because sea otters do not have any insulating fat, the fur is responsible for heat maintenance. |
| Sea otters are considered a keystone species: they play a major role in their community by controlling plant-eating invertebrates | They are considered a keystone species and play a major role in the community by controlling herbivorous invertebrates. (note: "Plant-eating" glosses "herbivorous".) |
| By preying on sea urchins, otters stop the urchins from overgrazing kelp forests, which lets the kelp thrive and adds to the variety of sea life | Sea otters prey on sea urchins, thereby preventing sea urchins from overgrazing the kelp forest. This allows the kelp forest to thrive and contributes to an increase in marine diversity. |
| Individual otters tend to specialize; one may eat only urchins and crabs while another eats mostly fish, depending on its skills and the food nearby | Individuals tend to be specialized in their choice of prey; one otter may consume only urchins and crabs while another may eat mostly fish, depending on the abilities of the individual and local food availability. |
| The variety in the sea otter's diet also reduces competition among the seafloor grazers it eats and supports greater diversity in those species | The variety in the sea otter diet reduces competition between benthic grazers and supports greater diversity in those species. (note: "Seafloor" glosses "benthic"; ADW lists these grazers (sea urchins, limpets, chitons) among the prey.) |
| By the turn of the 20th century, hunting had left between 1,000 and 2,000 sea otters worldwide | Sea otters were hunted to near extinction (1000 to 2000 individuals worldwide) ... until the turn of the 20th century |
| The 1911 International Fur Seal Treaty banned the hunt | the United States, Russia, Japan, and Great Britain reached an agreement in 1911 called the International Fur Seal Treaty, banning the hunting of fur-bearing sea mammals |
| The 1989 Exxon Valdez oil spill killed approximately 5,000 Alaskan sea otters | The Exxon Valdez oil spill of 1989 had a dramatic effect on the Alaskan sea otter population, killing approximately 5,000 individuals. (note: A past event, so the ADW page's age does not date it; no current page in the pack gives a different toll.) |
| Pockets of loose skin under its forearms store a tool, usually a rock, so its paws are free while it eats, and the same pockets carry food during dives | Sea otters have patches of loose skin under the forearms that they use to help store tools (usually a rock) so they can have free “hands” while eating, and to transport food during diving. |
| To break a hard shell, some otters hold the rock on their chest and drive the prey into it, while others lay the prey on their chest and hit it with the rock | Sea otters break open prey items with hard shells or exoskeletons with a rock. Some otters hold the rock on their chest and drive the prey into the rocks. Others leave the prey on their chests and hit the prey with the rocks. |
| An otter keeps the same rock for many dives | The same rock is kept for many dives. |
| Sea otters prey on sea urchins, which stops the urchins from overgrazing the kelp forest | Sea otters prey on sea urchins, thereby preventing sea urchins from overgrazing the kelp forest. |
| That lets the kelp forest thrive and adds to the variety of sea life there | This allows the kelp forest to thrive and contributes to an increase in marine diversity. |
| A keystone species is one whose loss from an area would eventually wipe out many more species there, and Animal Diversity Web names the sea otter as its example | a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter) (note: ADW's glossary entry for keystone species.) |
| Their fur, prized for its extreme density and insulating quality, was a major part of the fur trade from the mid 1700s to 1911 | The fur of sea otters was of great importance in the fur trade from the mid 1700s to 1911. Their fur was coveted due to its extreme density and insulating quality. |
| By the turn of the 20th century, hunting had left between 1,000 and 2,000 sea otters worldwide | Sea otters were hunted to near extinction (1000 to 2000 individuals worldwide) ... until the turn of the 20th century (note: Also covers the answer's opening "Very close." (ADW: "hunted to near extinction").) |
| The International Fur Seal Treaty banned the hunt in 1911 | reached an agreement in 1911 called the International Fur Seal Treaty, banning the hunting of fur-bearing sea mammals |

## Hughes et al. (2013). Recovery of a top predator mediates negative eutrophic effects on seagrass. Proceedings of the National Academy of Sciences.

https://doi.org/10.1073/pnas.1302805110

| The page says | The source says |
| :--- | :--- |
| In one estuary exposed to extreme nutrient pollution from farming, sea otters helped eelgrass, a seagrass, grow and spread, counteracting the harm those nutrients do | In a study of seagrass beds in an estuarine ecosystem exposed to extreme nutrient loading, we use a combination of a 50-y time series analysis, spatial comparisons, and mesocosm and field experiments to demonstrate that sea otters (Enhydra lutris) promote the growth and expansion of eelgrass (Zostera marina) through a trophic cascade, counteracting the negative effects of agriculturally induced nutrient loading. |

## Yeates, Williams & Fink (2007). Diving and foraging energetics of the smallest marine mammal, the sea otter (Enhydra lutris). Journal of Experimental Biology.

https://doi.org/10.1242/jeb.02767

| The page says | The source says |
| :--- | :--- |
| Researchers call the sea otter the smallest marine mammal | As the smallest and one of the most recently evolved marine mammals, sea otters face physiological challenges (note: The authors measured the energetics of resting, grooming, diving and foraging; the title calls the species "the smallest marine mammal".) |
| A foraging dive burns nearly twice the energy predicted for a seal, partly because of the otter's buoyancy and swimming style | The cost of a foraging dive for sea otters was nearly twice that predicted for phocid seals, which was attributed in part to elevated locomotor costs associated with buoyancy and swimming style. |

## Doroff, Burdin & Larson (2021). Enhydra lutris. The IUCN Red List of Threatened Species 2021: e.T7750A219377647.

https://doi.org/10.2305/iucn.uk.2021-3.rlts.t7750a219377647.en

| The page says | The source says |
| :--- | :--- |
| Endangered | Endangered (note: stats.conservationStatus; category read through GBIF's copy of the Red List.) |
| The latest IUCN Red List assessment, published in 2021, lists the sea otter as Endangered | Endangered (note: Category read through GBIF's copy of the Red List; the assessment (made in 2020) was published in the 2021-3 Red List update, as its DOI shows.) |
| today the IUCN Red List lists the sea otter as Endangered | Endangered (note: Category read through GBIF's copy of the Red List (2021 assessment, the latest).) |