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sea otter The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the smal ...
, ''Enhydra lutris'', is a member of the
Mustelidae The Mustelidae (; from Latin ''mustela'', weasel) are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, minks and wolverines, among others. Mustelids () are a diverse group and form the largest family in th ...
that is fully aquatic. Sea otters are the smallest of the
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
s, but they are also the most
dexterous Fine motor skill (or dexterity) is the coordination of small muscles in movement with the eyes, hands and fingers. The complex levels of manual dexterity that humans exhibit can be related to the nervous system. Fine motor skills aid in the gro ...
. Sea otters are known for their ability to use stones as anvils or hammers to facilitate access to hard-to-reach prey items. Furthermore, out of the thirteen currently known species of otters, at least 10 demonstrate stone handling behaviour, suggesting that otters may have a genetic predisposition to manipulate stones. Tool use behavior is more associated with geographic location than sub-species. Most behavioral research has been conducted on ''Enhydra lutris nereis'', the Californian otter, and some has been conducted on ''Enhydra lutris kenyoni'', the Alaska sea otter. Sea otters frequently use rocks as anvils to crack open prey, and they are also observed to rip open prey with their forepaws. While lying on their backs, otters will rip apart coral algae to find food among the debris.Hall, K. R. L., and George B. Schaller. "Tool-using Behavior of the California Sea Otter". Journal of Mammalogy 45.2 (1964): 287–298. The frequency of tool use varies greatly between geographic regions and individual otters. Regardless of the frequency, the use of tools is present in the behavioral repertoire of sea otters and is performed when most appropriate to the situation.


Evolution of tool use behavior


Selecting for certain behaviors

It is not possible to pin-point when sea otters began using tools consistently. It is hypothesized that certain behaviors were selected for, in the process of evolution, which led to this adaptation. The first instance of a rock as a tool may have occurred when an otter was unable to access a prey item at the bottom of the ocean and used a rock to facilitate access to the object. Similarly, an otter at the surface of the water may have chosen to crush two
bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
against each other when faced with an inability to crush the prey items with the forelimbs or teeth.Alcock, John. "The Evolution of the Use of Tools by Feeding Animals". Evolution 26.3 (1972): 464–473. Shellfish are found on rock structures at the bottom of the ocean, so collecting multiple rocks and shellfish from the bottom of the ocean in one diving episode and crushing the objects together on the surface may have led to the association of rocks with crushing shells of foods items. If a behavior which was performed in a conflict situation happened to open a prey item, an otter may have attempted to repeat the behavior and therefore learned to repeat the behavior consistently. Sea otters commonly exhibit swimming behavior where they swim on their backs. The features which facilitate swimming on the back also facilitate tool use. Otters that do not use tools still feed on their backs. This habit of feeding on the surface with the chest up facilitates a flat surface for resting rocks and pounding items together (1). Once discovered and consistently performed by one or some otters, the tool use behavior may have spread through a population of nearby otters by horizontal social learning. Tool use behaviors are observed in mammalian species where adults and their progeny have close ties. Mother otters have one pup at a time and sea otter pups are dependent on their mothers for an average of 6 to 7 months. Extremely young pups cannot swim or dive due to their natal fur coating, so they must be anchored to the mothers at all times. Otter pups therefore receive undivided attention from their mothers for prolonged periods of time. Similarly, young otters are observed to be exceptionally active, curious, and playful. Selection may have favored certain kinds of manipulatory play.


Skeletal changes

Sea otters belong to the order
Carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...
, whose members possess typical carnivoran teeth, or shearing
carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified f ...
s. These are blade-like teeth formed by an upper
premolar The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
and lower molar. Sea otters have replaced their carnassial teeth with
bunodont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
post-canines to improve their food crushing ability.Riedman, Marianne, and J. A. Estes. The Sea Otter (Enhydra Lutris): Behavior, Ecology, and Natural History. Washington, D.C.: U.S. Dept. of the Interior, Fish and Wildlife Service, 1990. Print. These teeth favor a diet of aquatic
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
s which is crucial to the otter's survival in the water. Sea otters also belong to the family
Mustelidae The Mustelidae (; from Latin ''mustela'', weasel) are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, minks and wolverines, among others. Mustelids () are a diverse group and form the largest family in th ...
. When compared with other mustelids, such as the river otter,
weasel Weasels are mammals of the genus ''Mustela'' of the family Mustelidae. The genus ''Mustela'' includes the least weasels, polecats, stoats, ferrets and European mink. Members of this genus are small, active predators, with long and slend ...
s, and
mink Mink are dark-colored, semiaquatic, carnivorous mammals of the genera '' Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": ...
s, the sea otter shows distinct
hindlimb A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hin ...
anatomy which could contribute to propulsion and stability at the surface of the water while the forelimbs manipulate tools and food. E. lutris has significantly larger gluteus muscles than other mustelids.Mori, Kent, Satoshi Suzuki, Daisuke Koyabu, Junpei Kimura, Sung-Yong Han, and Hideki Endo. "Comparative Functional Anatomy of Hindlimb Muscles and Bones with Reference to Aquatic Adaptation of the Sea Otter." Journal of Veterinary Medical Science The Journal of Veterinary Medical Science J. Vet. Med. Sci. (2015). Sea otter
forelimb A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial ( anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used inste ...
s are small and not used in swimming. Forelimb structure, particularly musculature and skeletal anatomy, are potentially adapted for, "tactile sensitivity and tool use associated with detection, handling, and consumption of prey".


Anatomy

The lower incisors of sea otters protrude and are shaped like spades, a shape which may facilitate their ability to scoop food out of
shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environ ...
.Estes, James A. "Enhydra Lutris." Mammalian Species 133 (1980): 1-9. During consumption of sea urchins, otters use a tool or their paws to crack open the
sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) o ...
s and scoop out the
gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...
s and
viscera In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...
with the lower incisors (12). The canines are blunt, and the post-canines are bunodont. Their flat and broad shape is useful for chewing a combination of soft invertebrates and the harder parts of tougher invertebrates, like shell fragments and sea urchin tests. Sea otters also have some of the largest lungs in the otter family, which may be helpful for
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...
, especially because sea otters do not have
blubber Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians. Description Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except fo ...
. Being buoyant along the length of the body allows otters to lie on their backs and manipulate food, tools, and young while on the surface of the water. Underneath the arm of each sea otter, at the axilla, is a flap of skin that can store stones and food. The hind legs are long and flattened like flippers, and the tail is also flattened. The tail moves in an undulating motion for propulsion. Paws and vibrissae work in tandem to find and grasp prey underwater.


Learning

It was found that orphaned juvenile sea otters in a research facility spontaneously developed stone tool use, without observing any models. Relatedly, stone handling behaviours were observed in 10 out of the 13 currently known subspecies of otters, including sea otters. Together, both studies suggest a genetic component to stone behaviours in otters – as this would explain both its occurrence without models and its cross-occurrence across species that do not observe each other. Otters that use stones to open prey do not use stones every time they need to manipulate their prey.
Crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
s, for example, can be ripped apart by the forelimbs and then eaten. Otters will store a stone in the pouch of skin under the arm to eat prey with both forelimbs, such as crabs, and then retrieve the stone at a later instance. Otters have been observed to use a clam shell as a digging tool and as a pry tool as well. This seems to imply, "an anticipation of use that goes beyond the immediate situation". If a stone appears to be particularly good for opening one food item, it will be kept for several others. In an observation of an otter in Point Lobos State Park, it was seen than one otter ate 44 mussels in one feeding episode and only used six stones.


Development

Sea otter development is marked by a six-month-long dependency period. Once an otter has adult-like swimming and diving behavior, can procure food by itself, and self-groom, it is considered independent.Payne, Susan F., and Ronald J. Jameson. "Early Behavioral Development of the Sea Otter, Enhydra Lutris". Journal of Mammalogy 65.3 (1984): 527–531. Until then, otter pups spend all of their time with their mothers. This is exacerbated by the fact that for the first three months of life, otter pups cannot swim or dive effectively. They are born with a natal
pelage Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket ...
that differs in color and structure from adult pelage and is incredibly buoyant. This prevents them from submerging their bodies underwater and must be held or anchored to
kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...
. Sea otter pups display a propensity for manipulating objects between their paws and regularly pound rocks and little bits of coral against their bodies in a random and curious manner. According to some of the earlier otter behavior biologists, Hall and Schaller, this, "tendency to manipulate and pound is far from stereotyped in its application and seems to prove the basis for learning the use of tools in feeding behavior". The first indications of tool use are observed at 5 weeks of age when pups will slap their forepaws against their chest. By ten weeks of age, they attempt consecutive dives with the same rock as they learn to swim.


Social transmission

Otters forage independently, except for females with offspring, who feed with their single young. Twins are observed but very rare. This allows for the mother otters to focus their attention on the pup, especially because mating occurs without pair bonding, so the father of the pup is not present. Pups express the same preferences in tools, technique, and diet as their mothers, which is potential evidence of vertical social transmission.Mann, J., and E. M. Patterson. "Tool Use by Aquatic Animals." Philosophical Transactions of the Royal Society B: Biological Sciences (2013). Overall, stone behavior likely also has a genetic component - this follows from the development of this behaviour in the absence of models, and from the fact that stone behavior occurs across a wide range of otter species. Mother otters appear to make sacrifices in order to help their pups. In Prince William Sound it was observed that, "the diet of females with pups was often of poor quality because the mothers frequently foraged on prey items that are easily captured by pups".


Current tool use behaviors

The foundation for observation studies of otters was conducted by scientists K. R. L. Hall and George B. Schaller in 1964. The scientists spent six days observing the Californian otters in Point Lobos State Park, California. Over the course of their time, they observed 30 separate instances of tool use behaviors, most of which involved otters using rocks to crack mussels. Since then, Californian sea otters have been studied extensively for their tool use behavior, garnering more attention to the subject, and serving as a model for what kinds of tool use behaviors the sea otter species is capable of performing. Sea otters do not seem to express preference for stones and rocks of a particular shape (smooth, sharp, flat, irregular), instead choosing ones that fall between a size range of , suggesting that size is more important than shape. Otters go on dives with their tools stored in specialized pouches of skin underneath the arms. A sea otter may capture more than two different food items on a single dive.


Diet

In all populations of sea otters, soft-bodied organisms such as
worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...
s and
sea stars Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ar ...
are the least likely to be consumed with the aid of tools. On the other hand, shelled bivalves and
snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class ...
s with shells are the most likely to be cracked open with tools.Fujii, J. A., K. Ralls, and M. T. Tinker. "Ecological Drivers of Variation in Tool-use Frequency across Sea Otter Populations." Behavioral Ecology 26.2 (2014): 519-26. Otters of the Northern Pacific consume mostly sea urchins and fish, thereby exhibiting less tool use behavior. Otters of the southern
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...
feed on tougher macro invertebrates such as bivalves. In central California, sea otters feed mostly on
sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) o ...
s,
abalone Abalone ( or ; via Spanish , from Rumsen ''aulón'') is a common name for any of a group of small to very large marine gastropod molluscs in the family Haliotidae. Other common names are ear shells, sea ears, and, rarely, muttonfish or mutto ...
s, and rock crabs. Rocks are used to knock abalones from the structure on which they are growing. Rocks can also be used to crack crab
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
s. Scientists have studied areas of California where up to 80% of abalone shells display crack patterns that are suggestive of breakage against rocks performed by otters. In areas near the
Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...
, less tool use is recorded and sea otters consume much more fish. The diet in these areas also includes sea urchins, which otters can break with their forepaws,
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
, and
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s.


Methods of tool use

Sea otters demonstrate at least three distinct methods of tool use. Two pertain to the use of stones and one pertains to the use of kelp as an anchor. Stones can be used as anvils, in which they are rested on the chest of an otter lying on the ocean surface. Hard prey items can be pounded against the anvil to create cracks and facilitate access to flesh. Stones can also be used as hammers, primarily to extract shellfish from their substrates. Other important aspects of otter tool-use behaviors include the use of tool composites and tool reuse. Tool composite is the term given to the combination of two rocks as an anvil and a hammer, separately, but used on the same prey item at once. Tool reuse is demonstrated by the use of the same stone in a variety of feeding opportunities over one large feeding period. There have also been observed instances of tool use methods which do not involve stone or kelp, but rather parts of the prey itself. These have been specifically seen as otters taking pieces of shell or crab carapace. Otters will take advantage of nearby objects, occasionally using, "empty shells, driftwood, empty glass, or other discarded man made objects. Live clams are also pounded against each other".


Stones as anvils

Sea otters most commonly use stones as anvils. They do not express a preference for the shape of the stone or rock, but they do choose fairly large stones, between , to rest on their chests. While all sub-species of otters use the forelimbs to rip open urchins, the Californian otters were observed to have used rocks as a surface to pound urchins and crabs, as well as mussels (observed most frequently). Otters seem to rise from a dive and immediately lie on the surface of the water with their chests up and place a stone on the chest to function as an anvil. The average length of a dive is 55 seconds. Otters hold mussels so as to orient the flat sides of the mussels against the "palms" of the paws and the seam of the two shells contacts the stone in a pounding instance. Mussels are pounded against rock or stones at a rate of two pounds per second. It takes approximately 35 blows to crack open a mussel.


Stones as hammers

In order to extract abalones from their substrate, otters demonstrate a hammering method by picking up rocks from the bottom of the ocean and hammering the abalone free from the substrate. Once on the surface, the otter may use the anvil method to continue to crack the abalone shell. Otters may also use a stone to hammer a prey item that is rested on the chest.


Kelp

Otters commonly wrap crabs in strands of kelp to immobilize them and leave the wrapped crabs on the chest while the otter eats other kinds of collected prey from the ocean bottom. Sea otters are familiar with kelp as a wrapping agent because they wrap themselves in kelp to remain in one location at the surface during periods of rest, or during sleeping. Mother otters also wrap their offspring in kelp when they cannot rest the pups on their chests.


Variation


Intra-species variation

Intra-species variation is observed with regards to the Northern Pacific and the Southern Pacific. In Point Lobos, the use of tools to open mussels is very common. This behavior is distinctly less common in northern areas like the
Commander Islands The Commander Islands, Komandorski Islands, or Komandorskie Islands (russian: Командо́рские острова́, ''Komandorskiye ostrova'') are a series of treeless, sparsely populated Russian islands in the Bering Sea located about ea ...
and
Kuril Islands The Kuril Islands or Kurile Islands (; rus, Кури́льские острова́, r=Kuril'skiye ostrova, p=kʊˈrʲilʲskʲɪjə ɐstrɐˈva; Japanese language, Japanese: or ) are a volcanic archipelago currently administered as part of Sakh ...
. There, adult otters only use tools if they are unable to open food items after trying first with their teeth.
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
n otters do not use tools as often as Californian otters. Californian otters show multiple techniques with differences that are tailored specifically to eating bivalves and crabs.Riedman, M. L., Staedier, M. M., Estes, J. A., & Hrabrich, B. 1989. The transmission of individually distinctive foraging strategies from mother to offspring in sea otters (Enhydra lutris). In Eighth Biennial Conference on the Biology of Marine Mammals. Pacific Grove, CA. A study that compiled seventeen years' worth of observational data demonstrated a significant difference between the occurrence of tool use in
Amchitka Amchitka (; ale, Amchixtax̂; russian: Амчитка) is a volcanic, tectonically unstable and uninhabited island in the Rat Islands group of the Aleutian Islands in southwest Alaska. It is part of the Alaska Maritime National Wildlife Ref ...
Island,
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...
and
Monterey, California Monterey (; es, Monterrey; Ohlone: ) is a city located in Monterey County on the southern edge of Monterey Bay on the U.S. state of California's Central Coast. Founded on June 3, 1770, it functioned as the capital of Alta California under b ...
. Alaskan otters used tools on 1% of dives, while Californian otters used tools on 16% of dives.


Sexual variation

All otter pups generally use tools if their mothers did. However, females are more likely to use tools to crush their prey in situations where the prey does not necessarily require a stone. It is suspected that matrilineal transmission can explain the observed female sex bias. Female otters also display more variation in the types of tool-use methods they employ.Tinker, M.t., D.p. Costa, J.a. Estes, and N. Wieringa. "Individual Dietary Specialization and Dive Behaviour in the California Sea Otter: Using Archival Time–depth Data to Detect Alternative Foraging Strategies." Deep-Sea Research Part II: Topical Studies in Oceanography 54.3 (2007): 330-42


Individual variation

During long-term studies to record behavior, it is frequently recorded that some, individual otters do not use tools at all. Instead, these otters target soft-bodied prey like fish, or urchins which can be ripped apart with the forelimbs. Among tool using otters, up to 21% of the day can be spent engaging in tool use. In a study conducted from Alaska to Southern California, sixteen otter populations demonstrated that individual diet specializations are much more likely to be present in environments of rocky habitat over soft sediment substrates.Newsome, Seth D., M. Tim Tinker, Verena A. Gill, Zachary N. Hoyt, Angela Doroff, Linda Nichol, and James L. Bodkin. "The Interaction of Intraspecific Competition and Habitat on Individual Diet Specialization: A near Range-wide Examination of Sea Otters." Oecologia 171.1 (2015): 45-59. Daughter Californian otters display the same tool techniques as their mothers, expressing explicit preference for certain methods when eating bivalves or eating crabs. In an aforementioned study, which compiled 17 years of observational data on otters from southern California to the Aleutian Islands, it was discovered that anywhere from 10% to 93% of individuals in a population use tools. Some otters have developed very specific, individual behaviors that do not necessarily demonstrate tool use, but do demonstrate dexterity. Individuals in California have learned how to tear open aluminum cans that float in the water from incidents of pollution. Small
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, ...
es commonly reside in the cans and the sea otters attempt to eat the small octopuses. Others have learned to reach on the
stern The stern is the back or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite the bow, the foremost part of a ship. Or ...
of small boats to obtain
bait fish 300px, Feeder Goldfish are common baitfish. Bait fish (or baitfish) are small-sized fish caught and used by anglers as bait to attract larger predatory fish, particularly game fish. Baitfish species are typically those that are common and bre ...
or
squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...
.


Paralytic shellfish poisoning

Otters are not immune to
paralytic shellfish poisoning Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfi ...
, despite some popular belief that they are. However, they have the ability to manipulate their prey enough to avoid the paralytic shellfish poisoning toxins so that they do not consume lethal amounts. Alaskan sea otters prey heavily on the butter clam, which has the ability to retain toxins obtained from
dinoflagellate The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
blooms. Captive sea otters were fed live butter clams in a study designed to test toxin avoidance and the otters discarded the siphons and kidneys before eating the clams. Most of the toxins are concentrated in these organs.Kvitek, Rikk G., Anthony R. Degange, and Mark K. Beitler. "Paralytic Shellfish Poisoning Toxins Mediate Feeding Behavior of Sea Otters." Limnol. Oceangr. Limnology and Oceanography 36.2 (1991): 393-404.


See also

*
Tool use by animals Tool use by animals is a phenomenon in which an animal uses any kind of tool in order to achieve a goal such as acquiring food and water, grooming, defence, communication, recreation or construction. Originally thought to be a skill possessed ...


References


Additional source

* Elin Kelsey, "The Quest for an Archaeology of Sea Otter Tool Use", Hakai Magazine, July 20, 2015


External links

{{Carnivora, M. Otters
otter Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the Mustelidae family, which also includes we ...