Photo Source: Adobe Stock Photos
TABLE OF CONTENTS:
- A Quick History Lesson [Background]
- Flips and Tricks [Physical Characteristics and Locomotion]
- To Sleep or Swim? [Energy Expenditures and Oxygen Consumption]
- Through the Seasons [Thermal Regulation and Fur Density]
- Breathe in... Breathe out [Respiratory system]
- A Seafood Diet [Nutrition and Digestive System]
- A Love Like No Otter [Reproduction and Relationships]
A Quick History Lesson
Background
THE ENHYDRA LUTRIS NEREIS
The California sea otter, also known as the Southern sea otter (Enhydra lutris nereis) is an endangered species belonging to the order Carnivora and Mustelidae family. Other members of the Mustelidae family include skunks and weasels. Some fun facts about these extraordinary marine mammals include their ability to survive their entire lives without leaving the ocean once, their ability to use tools, and their incredible fur, which gives them the title of the mammal with the densest fur! They are considered apex predators, and are also labeled as keystone species due to their importance in the marine ecosystem. Also having the title of sentinel species, their health statuses are direct reflections of the health of the California coastal ocean system.
NEAR EXTINCTION
In the 18th and 19th centuries, sea otters were hunted for their pelts, causing a massive decrease in the original population of an estimated 16,000 otters. The current population of living otters have all descended from the small group of 50 surviving otters that were discovered off of the Big Sur coastline in the early 1900s. The population grew again between the 1930s and 1980s, however an increase in net and trammel fisheries caused a decline in numbers again. Following the control of fisheries, the population grew until the mid 1990s, where there was another increase in mortality rates. The southern sea otter population number has since gradually regrown, however there has been a slight increase in mortality rates throughout recent years, primarily caused by Great White Shark bites off the coast of California, as well as oil spills and other climate impacts. Unfortunately, sea otters are still considered an endangered species according to the IUCN red list.
Photo Source: Adobe Stock Photos
Flips and Tricks
Physical Characteristics and Locomotion
Video Source: Monterey Bay Aquarium Youtube
Otters sure do love to swim and twirl, as seen in the video above! These functions are thanks to their spectacularly unique physiques and capabilities. Sea otters share many locomotion characteristics with smaller and larger marine relatives and other species, however, remain very unique in their structures and functions. Though they have the capability to move on land, wild sea otters tend to spend the majority, if not all of their lives out at sea, making swimming their primary form of locomotion.
Physical Characteristics
As mentioned previously, sea otters have quite a unique physique! Speaking broadly, otters (including river otters, sea otters, etc.) share very similar physical characteristics with one another, however, they do differ from one another in special ways. They all have very flexible bodies, allowing for adequate grooming and locomotion. Alongside their flexibility, all otters have four short legs, allowing them to swim, groom, and manipulate their choice of food (SeaWorld). Their fur, which will be covered to a deeper extent in the next section, carry characteristics of being fine, dense, and velvety.
To speak of the California Sea Otter specifically: the female California sea otter and the male California sea otter typically measure out with a generous weight difference! Male California sea otters average around 64 pounds (29 kg), while female California sea otters average around 44 pounds (20 kg). In comparison to their other otter species counterparts, sea otters are stockier due to having larger rib cages. They also exhibit typically darker brown shades (Figure 2.0).
Sea otters have very dexterous forepaws with retractable claws, which they use for grooming, finding food, eating, and lifting, however not for swimming! They instead swim using their flipper-like hind feet, which are webbed, large, and broad. Though they do not use their forepaws for swimming, they are the only marine mammal that have the ability to catch prey with their forepaws (Bentall et al., 2020). In comparison again with their other otter counterparts, sea otters have shorter and less muscular tails, using it mainly to turn when lying down and floating on their backs. The sea otter has a large, bare, black, and identifiably diamond-shaped nose, in which the females often have pink scars from wounds that were inflicted during mating. Sea otters have a total of 32 teeth (Figure 2.1) designed for crushing and grinding the shells of invertebrates, while lacking the function of breaking skin and flesh. They are interestingly the only carnivores with only four incisors on their lower jaw, which maintain the function of scraping the soft parts of mollusks.
Locomotion
As stated previously, sea otters that are not in captivity tend to live the majority, if not all of their lives out at sea. While sea otters and their otter species counterparts have the ability to move and survive on land, their primary form of locomotion tends to be swimming. Sea otters use their flipper-like hind legs to swim, while their forefeet are typically used for other activities, such as grooming, eating, etc. Sea otters demonstrate many adaptations known to enhance their swimming and reduce their transport costs while out in the water including body streamlining, large and specialized plantar surfaces for propulsion, and the ability to stay submerged for long and extended time periods (Williams, 1988). The style of swimming done by sea otters is called dorsoventral undulation- meaning wave-like, with a pairing of pelvic paddling (Figure 2.1). As they use this swimming mechanism, a wave produced through flexing and extending of the sea otters' backs, moves backwards along the body, acting as an assistant to the hind flippers, allowing for the generation of thrust during submersion.
The mechanism used by sea otters at the surface does not differ much from the dorsoventral undulation used when submerged, however it appears much different due to the speed in which they swim at the surface. As the otters swim on the surface of the water, there is a slight increase in drag experienced, as their bodies act similar to a displacement hull, thus causing a generation of waves. Within the resting position that otters are oftentimes photographed in, their dorsoventral undulation is traded with the supine position (flat on their backs) (Figure 2.2c), paired with alternating or simultaneous hind flipper strokes.
This positioning and rest comes extremely natural and easily to the sea otters due to the volume of their lungs. The typical sea otter lung volume is generally 3.3-fold greater than a land-animal of its same size, meaning that sea otters are quite buoyant creatures (Figure 2.2g). This buoyancy presents as both a blessing and a curse to sea otters, as it causes the necessity for them to actively swim in order to descend deeper into the ocean. Sea otters are also noted to leap out of the water using the power of their hind legs in order to descend past the surface at the beginning of their swim using momentum, and to overcome their buoyancy (Figure 2.3) (Davis, 2019).
To sleep or swim?
Energy Expenditures and Oxygen Consumption
Energy Expenditures
The sea otter metabolic rate is known to be quite high even in resting states. "Quite high" refers to the sea otter metabolic rate standing at a range of 2.8 to 3.2 times the metabolic rate level that is typically predicted of a land mammal with similar dimensions. The energy expenditure of sea otters is quantifiably large, due to the efforts made in swimming, eating, grooming, thermoregulating, and even resting.
The thermoregulatory costs are noticeably high due to body size and their form of insulation (Figure 3.0). Sea otters are highly dependent on their fur and the density of that fur. However, the fur density, in pair with large lung capacities, makes sea otters very buoyant. Buoyancy increases the energetic and mechanical costs of diving and remaining submerged, meaning that sea otters use lots of energy to do daily activities for survival (Fish et al., 2002). Though the pelt of the sea otter is dense and provides them with warmth through an air bubble layer within their underfur, sea otters must dive and fully submerge themselves in order to forage for food. As they do this, the otter reduces the quality of insulation provided by their fur, as the water compresses the air layer described previously. In order to compensate for an increase in thermal energetic costs, the sea otter typically shivers or eats large quantities of food in order to meet the energetic demands of its body.
Oxygen Consumption
Diving, foraging, and grooming behavior leads to an increase in VO2 over levels typically seen at rest, with resulting metabolic rates differing in significance between the different activities mentioned above (Yeates et al., 2007). The amount of oxygen consumed within a dive increases exponentially as the duration of a dive increases (Figure 3.1). Within a foraging dive, sea otters typically have higher energetic costs in comparison to non-foraging dives. It should be noted, however, that VO2 during submerged swimming by sea otters is almost half the rate of VO2 during surface swimming (Williams, 1988).
As sea otters spend high amounts of energy in grooming, swimming, and undergoing other activities in their day to day life, they typically perform these activities for short durations. Specifically looking at grooming, swimming, and interactions, 5.4 MJ day^-1 are usually used. The field metabolic rate of sea otters has been calculated to be 15.7 +/- 2.7 MJ day^-1 (Yeates et al., 2007). These metabolic rates cost high energetic expenditures daily, not to mention sea otter activity involving eating and simply fraternizing with one another. As body mass increases, there is also a noticeable increase in field metabolic rate in relation (Figure 3.2).
Through the Seasons
Thermal Regulation and Fur Density
Thermal Regulation
Sea otters must maintain many special adaptations in order to achieve successful thermoregulation while in their marine environments. Water transfers heat over 22 times as well as air, meaning that sea otters fight heat loss at a faster rate in water than on land. However, as mentioned before- sea otters rarely leave the water throughout their lives, thus requiring the adaptation of these mechanisms. These specialized adaptations are incredibly important, as sea otters are the only marine mammal that lacks blubber to keep them warm! In order to keep their body temperatures at the average 100°F, sea otters utilize their fur, metabolic rates, and muscles.
Sea otter fur, which will be covered more in depth within the next subsection, allows for sea otters to maintain their body temperature through a collection of air bubbles within their underfur. This underfur allows for the sea otter to maintain a barrier between itself and the ocean water, acting almost like a wetsuit! This fur is mostly water resistant, meaning the water does not get the chance to reach the otter's skin unless the pelt is penetrated (Morrison et al., 1974). As the sea otter maintains their body heat, relatively two-thirds of that heat escapes through their paws that are in the air or water, while another four-fifths will escape through the air in general.
The sea otter metabolism assists them in thermoregulation due to the extreme speed in which they can convert their food to energy. Otters are capable of burning through their food around three times as fast as another mammal of their size, thus requiring them to eat larger quantities of food in order to make up for lost energy, which boosts up their metabolism and allows their bodies to produce heat (Chambers, 2021). These boosts in heat production may also be accomplished by allowing their temperatures to fluctuate- in which they store heat during activity and appear to lose heat when resting. Sea otters also experience widespread vasoconstriction- in which their veins constrict when in cold temperatures, reducing the amount of heat loss. The sea otters utilize their flippers and paws in order to regulate heat loss by treating them as radiators to unload extra heat in the body. They use their flippers and paws specifically due to the rest of their body being highly insulated, while also considering that these areas have higher quantities of vasculature than the rest of the body. When they need to produce more heat, they are able to close their flippers and reduce the exposure of the flipper surface by one fourth. Sea otters tend to rest while holding their flippers and paws out of the water, which also assists in minimizing heat loss. The grooming patterns of sea otters involves licking their paws, head, and feet dry, thus reducing evaporative heat loss. The VO2 of sea otters while resting does not differ significantly when comparing their presence in warmer or cooler temperatures, however there is a significant increase in average and active VO2 as water temperature declines, thus describing the internal mechanisms at play when temperature declines and body temperature must rise (Figure 4.1) (Costa and Kooyman, 1981).
Fur Density
Known as the mammal with the densest fur, the sea otter is estimated to have a hair density between 120,000 and 140,000 hairs per cm^2, with relatively 600,000 to 1,000,000 hair follicles per square inch of their bodies. Sea otters have two hair types: the underfur- which traps the air bubbles that are kept within the pelt; and guard hairs- the longer, coarser strands of hair that extend beyond the underfur. They have been discovered to have bundles of 50 to 80 secondary hairs, with groups of 5 to 10 follicle bundles. This hair density is a necessity in order to live life as they do, typically in cool waters and other aquatic conditions. The density of their fur actively acts as a source of body insulation and heat conservation (Kuhn et al., 2009).
As explored in earlier sections, the Enhydra lutris is highly buoyant due to their lung capacities. Alongside their massive lungs, their incredible fur density plays a large part in their buoyancy. Because their hair is so dense, their pelts have the ability to carry large quantities of air pockets, which work together with their lungs to create their spectacular buoyancy. It has been calculated that buoyancy increases linearly with hair density, proving that their fur contributes largely to this mechanism (Figure 4.3). On a less convenient note, their buoyancy directly affects their energy expenditures due to the large amount of energy needed to dive and remain underwater. That being said, it is also very useful, as they often rest and feed while floating on their backs, thus nearly evening out energy costs by decreasing the amount of energy needed to stay afloat (Fish et al., 2002).
Given that their amazing fur is also waterproof, the sea otter is also protected against heat loss while in the water! It is easy to think of their fur almost like a wetsuit that surfers wear. Wetsuits maintain a person's body heat by trapping water inside of the suit, which then gets heated by the natural body heat that humans emit. Similarly, sea otters' pelts allow for them to trap their body heat instead of losing it to the ocean. Though these pelts give tremendous advantage to the sea otter species, it can be easily ruined through water infiltration, causing a compression of fur. In order to combat this struggle, sea otters must groom for approximately 11% of their days, causing an increase in metabolic rate to up to 64% above resting level (Fish et al., 2002). To groom their fur back to the ideal state, they will oftentimes use their forepaws to press into the fur in order to compress water out. They will also blow air into their fur in order to increase air supply within their underfur coat. They will also use their sharp and long forepaw claws to brush out the tangles in their fur. Luckily, their coats are surprisingly quite loose on their skin, meaning there is little to no tension when they make any movements, which allows for them to be able to groom, move, swim, dive, and eat!
breathe in... breathe out
Respiratory System
Respiratory System
As mentioned, the sea otter has the capability to store immense amounts of oxygen thanks to their large lung capacities. While giving the sea otter high levels of buoyancy, its lung capacity also serves as the otters' lifeline during foraging dives, in which the sea otter dives down to the ocean floor and swims back up to the surface prior to eating.
ADL
ADL (aerobic dive limit) refers to the duration of time an animal can dive prior to their blood lactate concentration increasing above levels of rest, which indicates the shift from aerobic metabolism (Figure 5.0) to anaerobic metabolism (Figure 5.1) (Thometz et al., 2015) . Anaerobic metabolism enables marine mammals to dive for longer durations, however, costs more energy in comparison to aerobic dives due to the energy needed to process the accumulated lactic acid concentrations in the body. ADL can be calculated by dividing total body oxygen storage by lung demand (Thometz et al., 2015).
In Relation to Buoyancy
The sea otter utilizes its buoyancy daily and quite often. The position in which the sea otter is laying on its back (supine) is used for when they eat, sleep, rest, etc., making it one of their go-to positions. This positioning would not be possible without the lung capacity of the sea otter. The sea otter, as mentioned previously, has a comparable lung size 3.3-fold larger than a land animal of similar size (Davis, 2019). Because of this, alongside the sea otter pelt, the sea otter stays afloat with ease, but is required to endure high positive buoyancy when attempting to dive.
Oxygen Storage
In order to endure the necessary foraging dives for food that only go down 20 m or less 69% of the time (Figure 5.2) (Thometz et al., 2015), the sea otter stores O2 within the lungs, blood, and muscles. Sea otters do not have any myoglobin within their central nervous system, thus having significant storage of O2 available to aerobic tissue only from the lungs and blood. The sea otters ensure to increase their lung volumes prior to each dive, as it is the only method that allows for an increase of O2 storage. While necessary, this method causes some difficulty throughout the actual dive, as buoyancy increases alongside it. Though they have massive lung capacities, a majority of the gas within each lung is N2, with O2 only being 15% of the lung (Kooyman, 1973).
Unlike the lung, sea otter blood O2 capacity is able to significantly increase without altering the total blood volume! They are able to do this by an increase of red blood cell count/volume, paired with an increase in hemoglobin.
The Pressure is Crushing!
As sea otters and other marine mammals dive down into the ocean, they combat the rapid changing hydrostatic pressure (Figure 5.2). This affects the lung system significantly during dives, as the lungs compress to a fraction of its original size. This decrease in lung size not only affects the storage of O2 and N2, but also constricts the flow of these important gasses to the central nervous system and the heart. The N2 storage in particular would be restricted from distributing around the entire body (Kooyman, 1973). This descent process can be highly dangerous for marine mammals, however sea otters are quite lucky, as they have lung capacities that are able to sustain them regardless of the hydrostatic pressure. There are also structures in place, such as cartilage surrounding airways in order to prevent constriction, which may assist in diving as well (Figure 5.3).
Through the Years
Sea otters grow to total oxygen storage capacity maturity very rapidly! Sea otter pups will reach the level of oxygen storage capacity maturity at a mere 2 months old. This phenomenon is due to their exceptional lung capacity at birth, which is followed closely by a decrease in mass-specific lung volume with age. However, regardless of maturity of lung capacity, the blood oxygen storage capacity remains significantly below levels of maturity until the sea otter pup is weaned off of their mothers. The ADLs of mature sea otters is expectedly longer than those of juvenile sea otters, mostly due to the increased oxygen demands and immature oxygen storage within juveniles (Thometz et al., 2015).
A SeAfood Diet
Nutrition and Digestive System
The sea otter reputation of being one of the cutest mammals alive is emphasized through their eating mechanisms! From the way they swim to the way they break their food open and eat, sea otters look great doing it, as seen in the video above.
Diet
The sea otter diet is of great importance. One of their favorite foods, sea urchins, is the reason behind their label of keystone species. Without sea otters, the sea urchin population grows past controllable limits and does severe harm to kelp populations. Besides sea urchins, the sea otter enjoys indulging in crabs, snails, clams, mussels, abalone, fish, etc. (Figure 6.0, 6.1) (Knight, 2022). Sea otters, as you may have gathered, are carnivorous species and primarily consume live prey.
Because they lack the layer of blubber that most marine mammals have, they must consume an average of 25% of their body weight in order to survive, meaning the average sized sea otter eats around 4-5 kg of food daily (Knight, 2022). Sea otter diet specializations have been noted to be passed on through matrilineal transmission- meaning that sea otter pups typically gain their diet and foraging habits from their mothers (Ostfeld, 1982).
Foraging Behavior
Sea otters utilize many capabilities in their forages. They are described as solitary and tactile foragers, meaning that they are not constrained by other species in their access to foods (Fujii et al., 2017). They are forepaw oriented- meaning they use their forepaws to manipulate and capture food instead of their mouths (Davis and Bodkin, 2021). Foraging involves diving to depths as low as 20 meters below the surface to reach sub-tidal reef habitats or soft-bottom environments (Honka, 2009). In order to reach their intended location, they must work hard to fight their natural buoyancy by leaping into the air and generating thrust in order to submerge themselves. In order to remain submerged, they use dorsoventral undulation and pelvic paddling (Figure 6.4) (see LOCOMOTION). The mean duration of dives that are less that 10 meters deep is measured at 0.7 minutes, while deeper dives that are over 15 meters deep are on average 1.6 minutes long. There is a positive correlation between dive length and depth due to ADL (see RESPIRATION). Though this correlation is very typical, shallow dives have the capability to last just as long as deeper dives (Figure 6.3). They dive down with their eyes open in order to target their prey, and they remain open throughout the remainder of their forage (Davis and Bodkin, 2021).
When the sea otters reach their desired prey, they either grab them with their forepaws or utilize rocks to break and/or scrape prey off of rocks and stuff them in the pouches that they have under each forepaw armpit, where they also keep their favorite tool. Sea otters are the only marine mammal capable of lifting rocks underwater, which is where they typically will find their prey. After they collect their desired amount of prey, they return to the surface in order to eat (Figure 6.2) (Ostfeld, 1982).
As sea otter populations migrate to new territories, they initially choose to eat optimal prey (i.e. sea urchins), but as time goes on and the population densities approach equilibrium, their diet begins to expand and assort past the optimal prey. This is mostly due to the optimal prey population depleting over time (Laidre and Jameson, 2006).
Tools and How They Eat
For a long time, sea otters were one of the only animals that were observed to use tools. Sea otters often use tools for collecting prey and opening or cracking the shells of their prey for consumption. The prey of choice typically dictates whether or not the sea otter uses tools to assist them in their meals, depending on the morphology of the prey (Figure 6.6). There are many other factors that have been noted to influence the use or non-use of tools, including gender and age (Figure 6.7). For example: adult females are more likely to use tools in comparison to their adult male counterparts and younger females.
Tools typically consist of rocks, empty shells, other prey, bottles, or plastic. They have been observed to pick a favorite tool and keep it tucked under their arms within their forepaw armpit pockets. When orphaned pups were exposed to tools, they were able to use them without prior training. Juvenile pups also show this cognitive ability by practicing banging shells or rocks together. Similar to diet specialization, tool usage is also affected by the amount and frequency that their mothers use tools, making it another matrilineal adapted mechanism (Fujii et al., 2017). In order to eat, sea otters utilize their bottom incisors to scrape food off of their shells (Figure 6.5).
Digestive System
When sea otters eat, the food that they consume is stored as glucose, which is later used for energy, as mentioned previously. The sea otter has a closed circulatory system, alongside a complete digestive system. The digestive system is composed of the liver, pancreas, gallbladder, and gastrointestinal tract. The gastrointestinal tract then includes the small and large intestine, stomach, and rectum. The sea otter actually does not have a cecum- which is the pouch typically connected to the small and large intestine, that has the function of assisting the body by digesting absorbed liquids.
A Love like no otter
Reproduction and Relationships
Social System
Contrary to the title of this section, sea otter reproductive relations are quite interesting and do not involve much love or kind nature. The reproductive system that sea otters follow is referred to as resource defense polygyny (Pearson and Davis, 2021). This system involves male sea otters defending territories containing resources that will attract foraging females. Due to this system, the social-sexual behavior observed within the sea otter population involves segregation by age and sex.
Reproductive Physiology
Though male sea otters reach sexual maturity between the ages of 5 and 6, they do not reach social maturity for a few more years. Social maturity refers to the ability for them to defend territory and thus, mate. The reproductive anatomy of males involves a vascular penis reinforced by the penile bone called the baculum. The baculum contains an attachment of ligaments to the ischium and assists in sexual intercourse by initiating and maintaining stiffness. A pair of testes are visible on male sea otters as they lay in the resting supine position, which are formed by the baculum and scrotum containing the penile ridge (Figure 7.0) (Pearson and Davis, 2021).
Sea otters do not have a specific breeding season, meaning that newborn pups appear year-round. The ejaculate of male sea otters hold similarity to their other male mammal counterparts, while female sea otters hold similarity to other members of the Mustelidae family. Female sea otters experience a rise in the luteinizing hormone following sexual activity. Paired with the longevity of semen presence within the reproductive tract, female sea otters facilitate fertilization. Female sea otter reproduction compiles three phases over a single year span. These include: Phase 1 (2-3 months)- estrus, copulation, and delayed implantation; Phase 2 (4-5 months)- implantation, gestation, and parturition; and Phase 3 (5-6 months)- pup care through weaning (Chinn et al., 2016).
Birth Process
Similarly to other mammals, female sea otters birth vaginally after a gestation period of four to nine months (SeaWorld). Unlike any other marine mammal, the female sea otter gives birth in the ocean. Most females breed within the fifth and sixth year of their lives for the very first time, joining the 85-90% of female otters the may give birth in a single year span (Jameson and Johnson, 1993). Pups are born around 56 to 61 cm long and weigh approximately 2 to 2.3 kg. They are born with their eyes open and some teeth that are beginning to emerge. They are also born with their notoriously dense fur! Pups may begin to swim and consume solid food at about one month old, and soon after learn how to dive and begin their forage process.
Relationships
Between Competing Males
As mentioned earlier in this section, male sea otters must fight to defend their territory in order to attract mates. Because of this, male sea otters exhibit large amounts of territorial behavioral traits and typically fight one another in order to win the rights to the area (Figure 7.1) (Pearson and Davis, 2021). Due to these interactions, male sea otters also exhibit pink or brown scars on their noses, similar to their female counterparts.
Between Female and Male
As female sea otters approach a male sea otter's territory, the male approaches slowly in order to gauge reproductive/sexual reception, then relies on pheromones to continue the mating process. In order to hold the female sea otter in place to begin sexual intercourse, the male sea otter grasps the female on the nose with his teeth (Figure 7.2), causing the pink or brown scarring present on many female sea otters' noses. The coital process typically involves wrestling and thrashing, thus causing deep marks in the female's noses and sometimes fatality to the female by drowning. Once female sea otters mate a single time during a season, they are unlikely to mate again with any male, including the one she already mated with, as they have the tendency to leave and abandon their previous mate (Pearson and Davis, 2021).
Between Mother and Juvenile Pup
Females are the only parental figure that provides care for a sea otter pup. Seen in the featured photo, female sea otters (mothers) will carry their pup(s) on their stomachs while resting in supine position. The sea otter mother proceeds care and investment for typically 19-26 weeks in order to wean her pup successfully. Periods of care extending beyond the 26 weeks almost guarantees a higher survival rate for the pup. Pups typically nurse for approximately 5-6 months of dependency and consume prey captured by their mother's foraging skills. For the first 10 weeks of the pups life, the mother will limit her foraging to short depths and durations in order to ensure the pup's safety. Because of these relations, alongside lactation costs, the mother sea otter experiences sharp challenges against her energy costs and production (Chinn et al., 2016). The daily energy demands of a postpartum adult female sea otter increases by 17% at 3 weeks after giving birth and increases even further to a 96% increase at the weaning stage (Thometz et al., 2014)(Thometz et al., 2016). As the pup spends 5-12 months with their mother, they are often included in rafts, which are groups of same-sex sea otters that often times hold hands in order to ensure their security and protect the raft from drifting apart (Figure 7.3).
Between Female and Female
While both male and female sea otters spend a majority of their time alone, female sea otters tend to find themselves within groups called rafts, mentioned in the previous subsection (Figure 7.3). Within these rafts, the adult sea otters hold hands while sleeping or resting in order to stay together. They oftentimes will also hold on to kelp or other stationary oceanic features in order to maintain their position in the ocean (Natural History on the Net)
REFERENCES
PRIMARY LITERATURE
ARTICLES
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Ostfeld, Richard S. “Foraging Strategies and Prey Switching in the California Sea Otter.” Oecologia, vol. 53, 1982, pp. 170–178., https://link.springer.com/content/pdf/10.1007/BF00545660.pdf?pdf=button.
Pearson, Heidi C., and Randall W. Davis. “Reproductive Behavior of Male Sea Otters.” Ethology and Behavioral Ecology of Sea Otters and Polar Bears, 4 July 2021, pp. 107–123., https://doi.org/10.1007/978-3-030-66796-2_6.
Thometz, N. M., et al. “Energetic Demands of Immature Sea Otters from Birth to Weaning: Implications for Maternal Costs, Reproductive Behavior and Population-Level Trends.” Journal of Experimental Biology, vol. 217, no. 12, 15 June 2014, pp. 2053–2061., https://doi.org/10.1242/jeb.099739.
Thometz, Nicole M., et al. “Ontogeny of Oxygen Storage Capacity and Diving Ability in the Southern Sea Otter (Enhydra Lutris Nereis): Costs and Benefits of Large Lungs.” Physiological and Biochemical Zoology, vol. 88, no. 3, 2015, pp. 311–327., https://doi.org/10.1086/681019.
Thometz, Nicole M., et al. “The High Cost of Reproduction in Sea Otters Necessitates Unique Physiological Adaptations.” Journal of Experimental Biology, vol. 219, no. 15, 1 Aug. 2016, pp. 2260–2264., https://doi.org/10.1242/jeb.138891.
Williams, Terrie M. “Swimming by Sea Otters: Adaptations for Low Energetic Cost Locomotion.” Journal of Comparative Physiology A, vol. 164, no. 6, 1989, pp. 815–824., https://doi.org/10.1007/bf00616753.
Yeates, Laura C., et al. “Diving and Foraging Energetics of the Smallest Marine Mammal, the Sea Otter (Enhydra Lutris).” Journal of Experimental Biology, vol. 210, no. 11, 2007, pp. 1960–1970., https://doi.org/10.1242/jeb.02767.
GRAY LITERATURE
WEBSITES
Admin. “Information about the Sea Otter.” Natural History on the Net, 18 July 2016, https://www.naturalhistoryonthenet.com/Mammals/sea_otter.htm.
“Birth & Care of Young.” SeaWorld Parks & Entertainment, https://seaworld.org/animals/all-about/otters/care-of-young/.
Chambers, Jaime. “Here's How Sea Otters Stay Warm without Blubber or a Large Body.” Science News Explores, 11 Oct. 2021, https://www.snexplores.org/article/heres-how-sea-otters-stay-warm-without-blubber-or-a-large-body.
“Digestive System.” Sea Otters, https://zoolog-otters.weebly.com/digestive-system.html.
Harding, Bryan. “How Do Otters Communicate?” North American Nature, North American Nature, 27 Dec. 2020, https://northamericannature.com/how-do-otters-communicate/.
Knight, Peralee. “What Do Sea Otters Eat?” AZ Animals, 12 Jan. 2022, https://a-z-animals.com/blog/what-do-sea-otters-eat/.
Nutrition, 2008, http://bioweb.uwlax.edu/bio203/s2008/bluske_brit/Nutrition.htm.
“Physical Characteristics.” SeaWorld Parks & Entertainment, https://seaworld.org/animals/all-about/otters/characteristics/.
“Sea Otter Natural History.” SeaOtters.com, https://www.seaotters.com/sea-otter-natural-history/.
BOOKS
Davis, R.W. (2019). Locomotion. In: Marine Mammals. Springer, Cham. https://doi.org/10.1007/978-3-319-98280-9_5
McLeish, Todd. Return of the Sea Otter the Story of the Animal That Evaded Extinction on the Pacific Coast. Sasquatch Books, 2018.
OTHER GRAY LITERATURE
Bentall, Gena, et al., editors. Sea Otter Enhydra Lutris, Manta Publications, Malibu, California, 2020.
FIGURE SOURCES
FIGURE 1.0: https://www.mmc.gov/priority-topics/species-of-concern/southern-sea-otter/
FIGURE 2.0: https://www.exploringnature.org/graphics/bw_diagram/otter_sea_diagram_bw150.jpg
FIGURE 2.1: https://www.seaotters.com/sea-otter-natural-history/
FIGURE 2.2, 2.3, 2.4: https://link.springer.com/chapter/10.1007/978-3-319-98280-9_5#citeas
FIGURE 3.0: https://www.science.org/doi/10.1126/science.abf4557
FIGURE 3.1, 3.2: https://doi.org/10.1242/jeb.02767
FIGURE 4.0: https://www.sunnyskyz.com/happy-videos/10646/Concerned-Sea-Otter-Gets-Its-Temperature-Taken
FIGURE 4.2: https://rangerrick.org/zoobooks/a-sea-otters-coat-is-very-special/
FIGURE 5.0: https://biologydictionary.net/aerobic-respiration/
FIGURE 5.1: https://biologydictionary.net/anaerobic-respiration/
FIGURE 5.2: https://www.tec-science.com/mechanics/gases-and-liquids/applications-and-examples-of-hydrostatic-pressure/
FIGURE 5.3: https://academic.oup.com/icb/article/13/2/457/1999217
FIGURES 6.0, 6.2, 6.3, 6.4, 6.5: https://link.springer.com/chapter/10.1007/978-3-030-66796-2_4
FIGURE 6.1: https://link.springer.com/content/pdf/10.1007/BF00545660.pdf?pdf=button
FIGURES 6.6, 6.7: https://academic.oup.com/beheco/article/28/5/1206/4001444
FIGURES 7.0, 7.1, 7.2: https://link.springer.com/chapter/10.1007/978-3-030-66796-2_6
FIGURE 7.3: http://www.folomojo.com/sea-otters-hold-hands-while-sleeping-is-the-cutest-thing-youll-ever-see/
PHOTO SOURCES
https://abcnews.go.com/US/newborn-sea-otter-pup-bonds-mother-adorable-photos/story?id=37496814
https://twitter.com/montereyaq/status/1265703807339556864?lang=ar-x-fm
https://www.montereybayaquarium.org/animals/animals-a-to-z/sea-otter
https://zoolog-otters.weebly.com/respiration.html
https://seaworld.com/san-diego/blog/otter-diet-facts/
https://fws.gov/project/protection-northern-sea-otters-washington
https://www.marinemammalcenter.org/animal-care/learn-about-marine-mammals/sea-otters
https://www.flickr.com/photos/mosesharold/26723608074
VIDEO LINKS
Credits:
Created with images by nvphoto - "Sea otter floating in the water" • David McGowen - "Sea Otter close up in Alaska" • Luis - "The sea otter, a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Vancouver, British Coiumbia, Canada" • Andy Morehouse - "colony of sea otters"