Aquatic locomotion
Encyclopedia
Swimming is biologically propelled motion through a liquid medium. Swimming has evolved a number of times in a range of organisms ranging from arthropod
s to fish
to molluscs.
, but the first free-swimming animals appear in the Early to Middle Cambrian
. These are mostly related to the arthropod
s, and include the Anomalocaridids, which swam by means of lateral lobes in a fashion reminiscent of today's cuttlefish
. Cephalopods joined the ranks of the nekton
in the late Cambrian, and chordates were probably swimming from the Early Cambrian. Many terrestrial animals retain some capacity to swim, however some have return to the water and developed the capacities for aquatic locomotion.
, jellyfish and their kin, the main form of swimming is to flex their cup shaped bodies. All jellyfish
are free-swimming, although many of these spend most of their time swimming passively. Passive swimming is akin to gliding; the organism floats, using currents where it can, and does not exert any energy into controlling its position or motion. Active swimming, in contrast, involves the expenditure of energy to travel to a desired location.
In bilateria
, there are many methods of swimming. The arrow worms (chaetognatha
) undulate their finned bodies, not unlike fish. Nematode
s swim by undulating their fin-less bodies. Some Arthropod
groups can swim. Many crustacean
s can swim. Most, such as shrimp
, will usually swim by paddling with special swimming legs (pleopods), however some arthropods can also propel themselves backwards quickly by flicking their tail, known as the Caridoid escape reaction
. Swimming crabs swim with modified walking legs (pereiopods). Daphnia
, an crustacean, swims by beating it antenna instead.
There are also a number of forms of swimming molluscs. Many free-swimming sea slug
s, such as sea angel
s, flap fin-like structures. Some shelled molluscs, such as scallop
s can briefly swim by clapping their two shells open and closed. The molluscs most evolved for swimming are the cephalopod
s.
All cephalopods can move by jet propulsion
, but this is a very energy-consuming way to travel compared to the tail propulsion used by fish. The relative efficiency of jet propulsion decreases further as animal size increases. Since the Paleozoic, as competition with fish produced an environment where efficient motion was crucial to survival, jet propulsion has taken a back role, with fins and tentacles used to maintain a steady velocity. The stop-start motion provided by the jets, however, continues to be useful for providing bursts of high speed - not least when capturing prey or avoiding predators. Indeed, it makes cephalopods the fastest marine invertebrates, and they can outaccelerate most fish. Oxygenated water is taken into the mantle cavity
to the gill
s and through muscular contraction of this cavity, the spent water is expelled through the hyponome
, created by a fold in the mantle. Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions. Most cephalopods float (i.e. are neutrally buoyant
), so do not need to swim to remain afloat.
Among the Deuterostomia, there are a number of swimmers as well. Feather stars can swim by undulating their many arms http://video.mx.msn.com/watch/video/beautiful-swimming-feather-star/8dw7iajz. Salp
s move by pumping waters through their gelatinous bodies. The deuterosomes most evolved for swimming are found among the vertebrate
s, notably the fish
.
Hydrozoan medusae, which use a one-way water cavity design, generate a phase of continuous cycles of jet-propulsion followed by a phase of rest. The Froude efficiency is measured to be at 0.09, which shows a very costly method of locomotion. The metabolic cost of transport for the medusa is high when compared to a fish of equal mass. Other jet-propelled animals have similar problems in efficiency. Scallops, which use a similar design, swim by quickly opening and closing their shells, which draws in water and expels it from all sides. This locomotion is used as a means to escape predators such as starfish. Afterwards, the shell acts as a hydrofoil to counteract the scallop’s tendency to sink. The Froude efficiency is low for this type of movement, about 0.3, hence why it’s used as an emergency escape mechanism from predators. However, the amount of work the scallop has to do is mitigated by the elastic hinge that connects the two shells of the bivalve. Squids swim by drawing and expelling water through their siphon and into their mantle cavity. The Froude efficiency of their jet-propulsion system is around 0.29, which is much lower than a fish of the same mass. Squid swim more slowly than fish, but use more power to generate their speed. The loss in efficiency is due to the amount of water the squid can accelerate out of its mantle cavity.
• Subcarangiform, Carangiform, Thunniform: <1 wavelength while swimming at any point, undulates posterior half of body, fast swimmers
• Ostraciform: oscillates caudal region, slow swimmers (cowfish appear to hover in column by employing ostraciiform)
• Rajiform, Amiiform, Gymnotiform: undulate pectorals and median fins, >1 wavelength while swimming at any point, slow to moderate swimmers
• Labriform: oscillate pectoral fins, slow swimmers
• Turtles and penguins beat paired hydrofoils
• Dolphins, whales – very many long, compliant, slender tendons from penduncle to fluke
• Porpoising (cetaceans, penguins, pinnipeds) may save energy if they are moving fast – drag increases with speed, so the work required to swim unit distance is greater at higher speeds, but the work needed to jump unit distance is independent of speed.
• Seals propel with their tail, sea lions solely with pectoral flippers
• Tuna – large, stiff tendons – peak inertial forces act when the tail is at extremes at its left and right motions
Appendages of aquatic organisms propel them in two main and biomechanically extreme mechanisms. Some use lift powered swimming, which can be compared to flying as appendages flap like wings, and reduce drag on the surface of the appendage. Others use drag powered swimming, which can be compared to oars rowing a boat, with movement in a horizontal plane, or paddling, with movement in the parasagittal plane. Drag swimmers use a cyclic motion where they push water back in a power stroke, and return their limb forward in the return or recovery stroke. When they push water directly backwards, this moves their body forward, but as they return their limbs to the starting position, they push water forward, which will thus pull them back to some degree, and so opposes the direction that the body is heading. This opposing force is called drag. The return-stoke drag causes drag swimmers to employ different strategies than lift swimmers. Reducing drag on the return stroke is essential for optimizing efficiency. For example, ducks paddle through the water spreading the webs of their feet as they move water back, and then when they return their feet to the front they pull their webs together, to reduce the subsequent pull of water forward. The legs of water beetles have little hairs which spread out to catch up and move water back in the power stroke, but lay flat as the appendage moves forward in the return stroke. Also, the water beetle’s legs have a side that is wider and is held perpendicular to the motion when pushing backward, but the leg is then rotated when the limb is to return forward, so that the thinner side will catch up less water.
The drag swimmers experience a lessened efficiency in swimming due to resistance which affects their optimum speed. The less drag a fish experiences, the more it will be able to maintain higher speeds. Morphology of the fish can be designed to reduce drag, such as streamlining the body. The cost of transport is much higher for the drag swimmer, and when deviating from its optimum speed, the drag swimmer is energetically strained much more than the lift swimmer. There are natural processes in place to optimize energy use, and it is thought that adjustments of metabolic rates can compensate in part for mechanical disadvantages.
Semi-aquatic animals compared to fully aquatic animals show exacerbation of drag. Design that allows them to function out of the water limits the efficiency possible to be reached when in the water. In water swimming at the surface exposes them to resistive wave drag and is associated with a higher cost than submerged swimming. Swimming below the surface exposes them to resistance due to return strokes, pressure and friction primarily. Frictional drag is due to fluid viscosity and morphology characteristics. Pressure drag is due to the difference of water flow around the body and is also affected by body morphology. Semi-aquatic organisms encounter increased resistive forces when in or out of the water, as they are not specialized for either habitat. The morphology of otters and beavers for example must meet needs for both environments. The fur they have decreases streamlining and creates additional drag. The platypus may be a good example of an intermediate between drag and lift swimmers because they have been shown to have a rowing mechanisms which is similar to a lift-based pectoral oscillation. The limbs of semi-aquatic organisms are reserved for use on land and using them in water not only increases the cost of locomotion, but limits them to drag-based modes.
Although they are less efficient, at low speeds drag swimmers are able to produce more thrust than lift swimmers. They are also thought to be better for maneuverability due to the large thrust produced.
ηf= 2U1(U1+ U2)
U1 = free stream velocity, U2 = jet velocity
Good efficiency for carangiform between 50-80%
, which creates a downstream force on the object. Frictional drag, on the other hand, is a result of fluid viscosity in the boundary layer. Higher turbulence causes greater frictional drag.
Reynolds number (Re) is the measure of the relationships between inertial and viscous forces in flow ((animal's length x animal's velocity)/kinematic viscosity of the fluid). Turbulent flow can be found at higher Re values, where the boundary layer separates and creates a wake, and laminar flow can be found at lower Re values, when the boundary layer separation is delayed, reducing wake and kinetic energy loss to opposing water momentum.
The body shape of a swimming organism affects the resulting drag. Long, slender bodies reduce pressure drag by streamlining, while short, round bodies reduce frictional drag; therefore, the optimal shape of an organism depends on its niche. Swimming organisms with a fusiform shape are likely to experience the greatest reduction in both pressure and frictional drag.
Wing shape also affects the amount of drag experienced by an organism, as with different methods of stroke, recovery of the pre-stroke position results in the accumulation of drag.
High-speed ram ventilation creates laminar flow of water from the gills along the body of an organism.
The secretion of mucus along the organism's body surface, or the addition of long-chained polymers to the velocity gradient, can reduce frictional drag experienced by the organism.
in the water. These structures, make the density of their bodies very close to that of the surrounding water. Some hydrozoans, such as siphonophores, has gas-filled floats; the Nautilus, Sepia, and Spirula (Cephalopods) have chambers of gas within their shells; and most teleost fish and many lantern fish (Myctophidae) are equipped with swim bladders. Many aquatic and marine organisms may also be composed of low-density materials. Deep-water teleosts, which do not have a swim bladder, have few lipids and proteins, deeply ossified bones, and watery tissues that maintain their buoyancy. Some sharks' livers are composed of low-density lipids, such as hydrocarbon squalene
or wax esters (also found in Myctophidae without swim bladders), which provide buoyancy.
Swimming animals that are denser than water must generate lift or adapt a benthic lifestyle. Movement of the fish to generate hydrodynamic lift is necessary to prevent sinking. Often, their bodies act as hydrofoils, a task that is more effective in flat-bodied fish. At a small tilt angle, the lift is greater for flat fish than it is for fish with narrow bodies. Narrow-bodied fish use their fins as hydrofoils while their bodies remain horizontal. In sharks, the heterocercal tail shape drives water downward, creating a counteracting upward force while thrusting the shark forward. The lift generated is assisted by the pectoral fins and upward-angle body positioning. It is supposed that tunas primarily use their pectoral fins for lift.
Buoyancy maintenance is metabolically expensive. Growing and sustaining a buoyancy organ, adjusting the composition of biological makeup, and exerting physical strain to stay in motion demands large amounts of energy. It is proposed that lift may be physically generated at a lower energy cost by swimming upward and gliding downward, in a "climb and glide" motion, rather than constant swimming on a plane.
Primarily or exclusively aquatic animals have re-evolved from terrestrial tetrapods multiple times: examples include amphibians such as newts, reptiles such as crocodiles, sea turtles, ichthyosaurs, plesiosaurs and mosasaurs, marine mammals such as whales, seals
and otters, and birds such as penguins. Many species of snakes are also aquatic and live their entire lives in the water.
Even though primarily terrestrial tetrapods have lost many of their adaptations to swimming, the ability to swim has been preserved or re-developed in many of them. It may never have been completely lost.
Examples are: Some breeds of dog
swim recreationally. Umbra, a world record-holding dog, can swim 4 miles (6.4 km) in 73 minutes, placing her in the top 25% in human long-distance swimming competitions. Although most cat
s hate water, adult cats are good swimmers. The fishing cat
is one wild species of cat that has evolved special adaptations for an aquatic or semi-aquatic lifestyle – webbed digits. Tigers and some individual jaguars are the only big cats known to go into water readily, though other big cats, including lions, have been observed swimming. A few domestic cat breeds also like swimming, such as the Turkish Van
. In an unpublished research carried out 2002 at the University of Bern (Switzerland), Bender & Hirt showed that the Turkish Van has less inhibition to enter in shallow water compared to another breed, the Russian Blue. This behavior can be partially explained by the character of the Turkish Van, who seems to be more curious and enterprising than other cat breeds (see Widmer 1990).
Horses, moose
, and elk
are very powerful swimmers, and can travel long distances in the water. Elephants are also capable of swimming, even in deep waters. Eyewitnesses have confirmed that camel
s, including Dromedary
and Bactrian
camels, can swim, despite the fact that there is little deep water in their natural habitats.
Both domestic and wild rabbit
s can swim. Domestic rabbits are sometimes trained to swim as a circus attraction. A wild rabbit famously swam in an apparent attack
on U.S. President Jimmy Carter
's boat when it was threatened in its natural habitat.
The Guinea pig
(or cavy) is noted as having an excellent swimming ability. Mice
can swim quite well. They do panic when placed in water, but many lab mice are used in the Morris water maze
, a test to measure learning. When mice swim, they use their tails like flagella and kick with their legs.
Many snakes are excellent swimmers as well. Large adult anaconda
s spend the majority of their time in the water, and have difficulty moving on land.
Humans do not swim instinctively, but nonetheless often feel attracted to water, showing a broader range of swimming movements than other non-aquatic animals. In contrast, many monkeys can naturally swim and some, like the proboscis monkey
, crab-eating macaque
, and Rhesus macaque
swim regularly.
Large primates other than humans generally do not like to swim. Wild chimpanzees and some gorillas will wade in very shallow water but will make no attempt to cross larger bodies of water. Orangutans don't swim instinctively but will attempt it under pressure or if learned.
Among invertebrates, a number of insect
species have adaptations for aquatic life and locomotion. Examples of aquatic insects
include dragonfly
larvae, water boatmen, and diving beetles. There are also aquatic spiders
, although they tend to prefer other modes of locomotion under water than swimming proper.
paintings from around 7,000 years ago. Competitive swimming started in Europe
around 1800 and was part of the first modern 1896 Summer Olympics
in Athens
, though not in a form comparable to the contemporary events. It was not until 1908 that regulations were implemented by the International Swimming Federation
to produce competitive swimming
.
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s to fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
to molluscs.
Evolution of swimming
Swimming evolved a number of times in unrelated lineages, and the evolutionary pressures leading to its adoption are unknown. Supposed jellyfish fossils occur in the EdiacaranEdiacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
, but the first free-swimming animals appear in the Early to Middle Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
. These are mostly related to the arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, and include the Anomalocaridids, which swam by means of lateral lobes in a fashion reminiscent of today's cuttlefish
Cuttlefish
Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda . Despite their name, cuttlefish are not fish but molluscs....
. Cephalopods joined the ranks of the nekton
Nekton
Nekton refers to the aggregate of actively swimming aquatic organisms in a body of water able to move independently of water currents....
in the late Cambrian, and chordates were probably swimming from the Early Cambrian. Many terrestrial animals retain some capacity to swim, however some have return to the water and developed the capacities for aquatic locomotion.
Invertebrates
Among the radiataRadiata
The Radiata are the radially symmetric animals of the Eumetazoa subkingdom. The term Radiata has had various meanings in the history of classification...
, jellyfish and their kin, the main form of swimming is to flex their cup shaped bodies. All jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
are free-swimming, although many of these spend most of their time swimming passively. Passive swimming is akin to gliding; the organism floats, using currents where it can, and does not exert any energy into controlling its position or motion. Active swimming, in contrast, involves the expenditure of energy to travel to a desired location.
In bilateria
Bilateria
The bilateria are all animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside. Radially symmetrical animals like jellyfish have a topside and downside, but no front and back...
, there are many methods of swimming. The arrow worms (chaetognatha
Chaetognatha
Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, that is belonging to the lowest zone of the ocean, or benthic zone, and can attach to algae and...
) undulate their finned bodies, not unlike fish. Nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s swim by undulating their fin-less bodies. Some Arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
groups can swim. Many crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s can swim. Most, such as shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, will usually swim by paddling with special swimming legs (pleopods), however some arthropods can also propel themselves backwards quickly by flicking their tail, known as the Caridoid escape reaction
Caridoid escape reaction
The Caridoid Escape Reaction, also known as lobstering or tail-flipping, refers to an innate escape mechanism in marine and freshwater crustaceans such as lobsters, krill, shrimp and crayfish....
. Swimming crabs swim with modified walking legs (pereiopods). Daphnia
Daphnia
Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
, an crustacean, swims by beating it antenna instead.
There are also a number of forms of swimming molluscs. Many free-swimming sea slug
Sea slug
Sea slug is a common name used for several different groups of saltwater snails that either lack a shell or have only an internal shell, in other words this name is used for various lineages of marine gastropod mollusks that are either not conchiferous or appear not to be.The phrase "sea slug" is...
s, such as sea angel
Sea angel
Sea angels previously known as one kind of pteropod, are a large group of small swimming sea slugs in six different families. These are pelagic marine opisthobranch gastropod molluscs in the clade Gymnosomata within the larger clade Heterobranchia....
s, flap fin-like structures. Some shelled molluscs, such as scallop
Scallop
A scallop is a marine bivalve mollusk of the family Pectinidae. Scallops are a cosmopolitan family, found in all of the world's oceans. Many scallops are highly prized as a food source...
s can briefly swim by clapping their two shells open and closed. The molluscs most evolved for swimming are the cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s.
All cephalopods can move by jet propulsion
Jet propulsion
Jet propulsion is motion produced by passing a jet of fluid in the opposite direction to the direction of motion. By conservation of momentum, the moving body is propelled in the opposite direction to the jet....
, but this is a very energy-consuming way to travel compared to the tail propulsion used by fish. The relative efficiency of jet propulsion decreases further as animal size increases. Since the Paleozoic, as competition with fish produced an environment where efficient motion was crucial to survival, jet propulsion has taken a back role, with fins and tentacles used to maintain a steady velocity. The stop-start motion provided by the jets, however, continues to be useful for providing bursts of high speed - not least when capturing prey or avoiding predators. Indeed, it makes cephalopods the fastest marine invertebrates, and they can outaccelerate most fish. Oxygenated water is taken into the mantle cavity
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
to the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s and through muscular contraction of this cavity, the spent water is expelled through the hyponome
Hyponome
A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda. In other words, a siphon is found in some saltwater and freshwater snails, in some clams, and in octopus, squid and relatives.Siphons in molluscs are tube-like...
, created by a fold in the mantle. Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions. Most cephalopods float (i.e. are neutrally buoyant
Neutral buoyancy
Neutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium. This offsets the force of gravity that would otherwise cause the object to sink...
), so do not need to swim to remain afloat.
Among the Deuterostomia, there are a number of swimmers as well. Feather stars can swim by undulating their many arms http://video.mx.msn.com/watch/video/beautiful-swimming-feather-star/8dw7iajz. Salp
Salp
A salp or salpa is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body...
s move by pumping waters through their gelatinous bodies. The deuterosomes most evolved for swimming are found among the vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, notably the fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
.
Jet Propulsion
Jet propulsion is a method of aquatic locomotion where animals fill a muscular cavity and squirt out water to propel them in the opposite direction of the squirting water. Most organisms are equipped with one of two designs for jet propulsion; they can draw water from the rear and expel it from the rear, such as jellyfish, or draw water from front and expel it from the rear, such as salps. Filling up the cavity causes an increase in both the mass and drag of the animal. Because of the expanse of the contracting cavity, the animal’s velocity fluctuates as it moves through the water, accelerating while expelling water and decelerating while vacuuming water. Even though these fluctuations in drag and mass can be ignored if the frequency of the jet-propulsion cycles is high enough, jet-propulsion is a relatively inefficient method of aquatic locomotion.Hydrozoan medusae, which use a one-way water cavity design, generate a phase of continuous cycles of jet-propulsion followed by a phase of rest. The Froude efficiency is measured to be at 0.09, which shows a very costly method of locomotion. The metabolic cost of transport for the medusa is high when compared to a fish of equal mass. Other jet-propelled animals have similar problems in efficiency. Scallops, which use a similar design, swim by quickly opening and closing their shells, which draws in water and expels it from all sides. This locomotion is used as a means to escape predators such as starfish. Afterwards, the shell acts as a hydrofoil to counteract the scallop’s tendency to sink. The Froude efficiency is low for this type of movement, about 0.3, hence why it’s used as an emergency escape mechanism from predators. However, the amount of work the scallop has to do is mitigated by the elastic hinge that connects the two shells of the bivalve. Squids swim by drawing and expelling water through their siphon and into their mantle cavity. The Froude efficiency of their jet-propulsion system is around 0.29, which is much lower than a fish of the same mass. Squid swim more slowly than fish, but use more power to generate their speed. The loss in efficiency is due to the amount of water the squid can accelerate out of its mantle cavity.
Elasticity in Jet Propulsion
Much of the work done by Scallop muscles to close its shell is stored as elastic energy in abductin tissue, which acts as a spring to open the shell. The elasticity causes the work done against the water to be low because of the large openings the water has to enter and the small openings the water has to leave. The inertial work of scallop jet-propulsion is also low. Because of the low inertial work, the energy savings created by the elastic tissue is so small that it’s negligible. Medusae can also use their elastic mesoglea to enlarge their bell. Their mantle contains a layer of muscle sandwiched between elastic fibers. The muscle fibers run around the bell circumferentially while the elastic fibers run through the muscle and along the sides of the bell to prevent lengthening. After making a single contraction, the bell vibrates passively at the resonant frequency to refill the bell. However, in contrast with scallops, the inertial work is similar to the hydrodynamic work due to how medusas expel water - through a large opening at low velocity. Because of this, the negative pressure created by the vibrating cavity is lower than the positive pressure of the jet, meaning that inertial work of the mantle is small. Thus, jet-propulsion is shown as an inefficient swimming technique.Swimming in fish
Many fish swim through water by creating undulations with their bodies. The undulations create components of forward thrust complemented by a rearward force, side forces which are wasted portions of energy, and a normal force that is between the forward thrust and side force. Different fish swim by undulating different parts of their bodies. Eel-shaped fish undulate their entire body in rhythmic sequences. Streamlined fish, such as salmon, undulate the caudal portions of their bodies. Some fish, such as sharks, use stiff, strong fins to create dynamic lift and propel them upwards.Body Caudal Fin (BCF) Propulsion
• Aguilliform: Anguilliform swimmers are typically slow swimmers. They undulate the majority of their body and use their head as the fulcrum for the load they are moving. At any point during their undulation, their body has an amplitude between 0.5-1.0 wavelengths. The amplitude that they move their body through allows them to swim backwards.• Subcarangiform, Carangiform, Thunniform: <1 wavelength while swimming at any point, undulates posterior half of body, fast swimmers
• Ostraciform: oscillates caudal region, slow swimmers (cowfish appear to hover in column by employing ostraciiform)
Median Paired Fin (MPF) Propulsion
• Tetraodoniform, Balistiform, Diodontiform: oscillate median fins, slow swimmers• Rajiform, Amiiform, Gymnotiform: undulate pectorals and median fins, >1 wavelength while swimming at any point, slow to moderate swimmers
• Labriform: oscillate pectoral fins, slow swimmers
Hydrofoils
• Create lift on paired fins• Turtles and penguins beat paired hydrofoils
• Dolphins, whales – very many long, compliant, slender tendons from penduncle to fluke
• Porpoising (cetaceans, penguins, pinnipeds) may save energy if they are moving fast – drag increases with speed, so the work required to swim unit distance is greater at higher speeds, but the work needed to jump unit distance is independent of speed.
• Seals propel with their tail, sea lions solely with pectoral flippers
• Tuna – large, stiff tendons – peak inertial forces act when the tail is at extremes at its left and right motions
Drag Powered Swimming
As with moving through any fluid, friction is created when molecules of the fluid collide with organism. The collision causes drag against moving fish, which is why many fish are streamlined in shape. Streamlined shapes work to reduce drag by orienting elongated objects parallel to the force of drag, therefore allowing the current to pass over and taper off the end of the fish. This streamlined shape allows for more efficient use of energy locomotion. Some flat-shaped fish can take advantage of pressure drag by having a flat bottom surface and curved top surface. The pressure drag created allows for the upward lift of the fish.Appendages of aquatic organisms propel them in two main and biomechanically extreme mechanisms. Some use lift powered swimming, which can be compared to flying as appendages flap like wings, and reduce drag on the surface of the appendage. Others use drag powered swimming, which can be compared to oars rowing a boat, with movement in a horizontal plane, or paddling, with movement in the parasagittal plane. Drag swimmers use a cyclic motion where they push water back in a power stroke, and return their limb forward in the return or recovery stroke. When they push water directly backwards, this moves their body forward, but as they return their limbs to the starting position, they push water forward, which will thus pull them back to some degree, and so opposes the direction that the body is heading. This opposing force is called drag. The return-stoke drag causes drag swimmers to employ different strategies than lift swimmers. Reducing drag on the return stroke is essential for optimizing efficiency. For example, ducks paddle through the water spreading the webs of their feet as they move water back, and then when they return their feet to the front they pull their webs together, to reduce the subsequent pull of water forward. The legs of water beetles have little hairs which spread out to catch up and move water back in the power stroke, but lay flat as the appendage moves forward in the return stroke. Also, the water beetle’s legs have a side that is wider and is held perpendicular to the motion when pushing backward, but the leg is then rotated when the limb is to return forward, so that the thinner side will catch up less water.
The drag swimmers experience a lessened efficiency in swimming due to resistance which affects their optimum speed. The less drag a fish experiences, the more it will be able to maintain higher speeds. Morphology of the fish can be designed to reduce drag, such as streamlining the body. The cost of transport is much higher for the drag swimmer, and when deviating from its optimum speed, the drag swimmer is energetically strained much more than the lift swimmer. There are natural processes in place to optimize energy use, and it is thought that adjustments of metabolic rates can compensate in part for mechanical disadvantages.
Semi-aquatic animals compared to fully aquatic animals show exacerbation of drag. Design that allows them to function out of the water limits the efficiency possible to be reached when in the water. In water swimming at the surface exposes them to resistive wave drag and is associated with a higher cost than submerged swimming. Swimming below the surface exposes them to resistance due to return strokes, pressure and friction primarily. Frictional drag is due to fluid viscosity and morphology characteristics. Pressure drag is due to the difference of water flow around the body and is also affected by body morphology. Semi-aquatic organisms encounter increased resistive forces when in or out of the water, as they are not specialized for either habitat. The morphology of otters and beavers for example must meet needs for both environments. The fur they have decreases streamlining and creates additional drag. The platypus may be a good example of an intermediate between drag and lift swimmers because they have been shown to have a rowing mechanisms which is similar to a lift-based pectoral oscillation. The limbs of semi-aquatic organisms are reserved for use on land and using them in water not only increases the cost of locomotion, but limits them to drag-based modes.
Although they are less efficient, at low speeds drag swimmers are able to produce more thrust than lift swimmers. They are also thought to be better for maneuverability due to the large thrust produced.
Fast Starts and Mauthner Response
Varieties of fish, such as teleosts, use fast-starts to escape from predators. Fast-starts are characterized by the muscle contraction on one side of the fish twisting the fish into a C-shape. Afterwards, muscle contraction occurs on the opposite side to allow the fish to enter into a steady swimming state with waves of undulation traveling alongside the body. The power of the bending motion comes from fast-twitch muscle fibers located in the central region of the fish. The signal to perform this contraction comes from a set of Mauthner cells which simultaneously send a signal to the muscles on one side of the fish. Mauthner cells are activated when something startles the fish and can be activated by visual or sound-based stimuli. Fast-starts are split up into three stages. Stage one, which is called the preparatory stroke, is characterized by the initial bending to a C-shape with small delay caused by hydrodynamic resistance. Stage two, the propulsive stroke, involves the body bending rapidly to the other side, which may occur multiple times. Stage three, the rest phase, cause the fish to return to normal steady-state swimming and the body undulations begin to cease. Large muscles located closer to the central portion of the fish are stronger and generate more force than the muscles in the tail. This asymmetry in muscle composition causes body undulations that occur in Stage 3. Once the fast-start is completed, the position of the fish has been shown to have a certain level of unpredictability, which helps fish survive against predators. The rate at which the body can bend is limited by resistance contained in the inertia of each body part. However, this inertia assists the fish in creating propulsion as a result of the momentum created against the water. The forward propulsion created from C-starts, and steady-state swimming in general, is a result of the body of the fish pushing against the water. Waves of undulation create rearward momentum against the water providing the forward thrust required to push the fish forward.Efficiency
Froude propulsion efficiency: ratio of power output to inputηf= 2U1(U1+ U2)
U1 = free stream velocity, U2 = jet velocity
Good efficiency for carangiform between 50-80%
Minimizing Drag
Pressure differences occur outside the boundary layer of swimming organisms due to disrupted flow around the body. The difference on the up- and down-stream surfaces of the body is pressure dragDrag
- In science and technology :* Drag , the force which resists motion of an object through a fluid* Drag equation, a mathematical equation used in analyzing the magnitude of drag caused by fluid flow...
, which creates a downstream force on the object. Frictional drag, on the other hand, is a result of fluid viscosity in the boundary layer. Higher turbulence causes greater frictional drag.
Reynolds number (Re) is the measure of the relationships between inertial and viscous forces in flow ((animal's length x animal's velocity)/kinematic viscosity of the fluid). Turbulent flow can be found at higher Re values, where the boundary layer separates and creates a wake, and laminar flow can be found at lower Re values, when the boundary layer separation is delayed, reducing wake and kinetic energy loss to opposing water momentum.
The body shape of a swimming organism affects the resulting drag. Long, slender bodies reduce pressure drag by streamlining, while short, round bodies reduce frictional drag; therefore, the optimal shape of an organism depends on its niche. Swimming organisms with a fusiform shape are likely to experience the greatest reduction in both pressure and frictional drag.
Wing shape also affects the amount of drag experienced by an organism, as with different methods of stroke, recovery of the pre-stroke position results in the accumulation of drag.
High-speed ram ventilation creates laminar flow of water from the gills along the body of an organism.
The secretion of mucus along the organism's body surface, or the addition of long-chained polymers to the velocity gradient, can reduce frictional drag experienced by the organism.
Buoyancy
Many aquatic/marine organisms have developed organs to compensate for their weight and control their buoyancyBuoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
in the water. These structures, make the density of their bodies very close to that of the surrounding water. Some hydrozoans, such as siphonophores, has gas-filled floats; the Nautilus, Sepia, and Spirula (Cephalopods) have chambers of gas within their shells; and most teleost fish and many lantern fish (Myctophidae) are equipped with swim bladders. Many aquatic and marine organisms may also be composed of low-density materials. Deep-water teleosts, which do not have a swim bladder, have few lipids and proteins, deeply ossified bones, and watery tissues that maintain their buoyancy. Some sharks' livers are composed of low-density lipids, such as hydrocarbon squalene
Squalene
Squalene is a natural organic compound originally obtained for commercial purposes primarily from shark liver oil, though plant sources are used as well, including amaranth seed, rice bran, wheat germ, and olives. All plants and animals produce squalene, including humans...
or wax esters (also found in Myctophidae without swim bladders), which provide buoyancy.
Swimming animals that are denser than water must generate lift or adapt a benthic lifestyle. Movement of the fish to generate hydrodynamic lift is necessary to prevent sinking. Often, their bodies act as hydrofoils, a task that is more effective in flat-bodied fish. At a small tilt angle, the lift is greater for flat fish than it is for fish with narrow bodies. Narrow-bodied fish use their fins as hydrofoils while their bodies remain horizontal. In sharks, the heterocercal tail shape drives water downward, creating a counteracting upward force while thrusting the shark forward. The lift generated is assisted by the pectoral fins and upward-angle body positioning. It is supposed that tunas primarily use their pectoral fins for lift.
Buoyancy maintenance is metabolically expensive. Growing and sustaining a buoyancy organ, adjusting the composition of biological makeup, and exerting physical strain to stay in motion demands large amounts of energy. It is proposed that lift may be physically generated at a lower energy cost by swimming upward and gliding downward, in a "climb and glide" motion, rather than constant swimming on a plane.
Secondary evolution of swimming
While tetrapods lost many of their natural adaptations to swimming when they evolved onto the land, many have re-evolved the ability to swim or have indeed returned to a completely aquatic lifestyle.Primarily or exclusively aquatic animals have re-evolved from terrestrial tetrapods multiple times: examples include amphibians such as newts, reptiles such as crocodiles, sea turtles, ichthyosaurs, plesiosaurs and mosasaurs, marine mammals such as whales, seals
Pinniped
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...
and otters, and birds such as penguins. Many species of snakes are also aquatic and live their entire lives in the water.
Examples are: Some breeds of dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
swim recreationally. Umbra, a world record-holding dog, can swim 4 miles (6.4 km) in 73 minutes, placing her in the top 25% in human long-distance swimming competitions. Although most cat
Cat
The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
s hate water, adult cats are good swimmers. The fishing cat
Fishing Cat
The Fishing Cat is a medium-sized wild cat of South and Southeast Asia. In 2008, the IUCN classified the fishing cat as endangered since they are concentrated primarily in wetland habitats, which are increasingly being settled, degraded and converted...
is one wild species of cat that has evolved special adaptations for an aquatic or semi-aquatic lifestyle – webbed digits. Tigers and some individual jaguars are the only big cats known to go into water readily, though other big cats, including lions, have been observed swimming. A few domestic cat breeds also like swimming, such as the Turkish Van
Turkish Van
The Turkish Van is a recognized cat breed that is known for its unusual love of water and swimming. They were created from the cats native to the Lake Van area of Turkey. The cats of this type are named in Turkish Van Kedisi , in Armenian vana katou or vana gadou and in Kurdish...
. In an unpublished research carried out 2002 at the University of Bern (Switzerland), Bender & Hirt showed that the Turkish Van has less inhibition to enter in shallow water compared to another breed, the Russian Blue. This behavior can be partially explained by the character of the Turkish Van, who seems to be more curious and enterprising than other cat breeds (see Widmer 1990).
Horses, moose
Moose
The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...
, and elk
Elk
The Elk is the large deer, also called Cervus canadensis or wapiti, of North America and eastern Asia.Elk may also refer to:Other antlered mammals:...
are very powerful swimmers, and can travel long distances in the water. Elephants are also capable of swimming, even in deep waters. Eyewitnesses have confirmed that camel
Camel
A camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as humps on its back. There are two species of camels: the dromedary or Arabian camel has a single hump, and the bactrian has two humps. Dromedaries are native to the dry desert areas of West Asia,...
s, including Dromedary
Dromedary
The dromedary or Arabian camel is a large, even-toed ungulate with one hump on its back. Its native range is unclear, but it was probably the Arabian Peninsula. The domesticated form occurs widely in North Africa and the Middle East...
and Bactrian
Bactrian camel
The Bactrian camel is a large, even-toed ungulate native to the steppes of central Asia. It is presently restricted in the wild to remote regions of the Gobi and Taklamakan Deserts of Mongolia and Xinjiang. A small number of wild Bactrian camels still roam the Mangystau Province of southwest...
camels, can swim, despite the fact that there is little deep water in their natural habitats.
Both domestic and wild rabbit
Rabbit
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world...
s can swim. Domestic rabbits are sometimes trained to swim as a circus attraction. A wild rabbit famously swam in an apparent attack
Jimmy Carter rabbit incident
The Jimmy Carter rabbit incident, dubbed the "killer rabbit" attack by the media, involved a Swamp Rabbit that caught press imagination after swimming toward then-U.S. President Jimmy Carter's fishing boat on April 20, 1979.-Background:...
on U.S. President Jimmy Carter
Jimmy Carter
James Earl "Jimmy" Carter, Jr. is an American politician who served as the 39th President of the United States and was the recipient of the 2002 Nobel Peace Prize, the only U.S. President to have received the Prize after leaving office...
's boat when it was threatened in its natural habitat.
The Guinea pig
Guinea pig
The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...
(or cavy) is noted as having an excellent swimming ability. Mice
MICE
-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...
can swim quite well. They do panic when placed in water, but many lab mice are used in the Morris water maze
Morris water maze
The Morris water navigation task is a behavioral procedure widely used in behavioral neuroscience to study spatial learning and memory. It was developed by neuroscientist Richard G...
, a test to measure learning. When mice swim, they use their tails like flagella and kick with their legs.
Many snakes are excellent swimmers as well. Large adult anaconda
Anaconda
An anaconda is a large, non-venomous snake found in tropical South America. Although the name actually applies to a group of snakes, it is often used to refer only to one species in particular, the common or green anaconda, Eunectes murinus, which is one of the largest snakes in the world.Anaconda...
s spend the majority of their time in the water, and have difficulty moving on land.
Humans do not swim instinctively, but nonetheless often feel attracted to water, showing a broader range of swimming movements than other non-aquatic animals. In contrast, many monkeys can naturally swim and some, like the proboscis monkey
Proboscis Monkey
The proboscis monkey or long-nosed monkey, known as the bekantan in Malay, is a reddish-brown arboreal Old World monkey that is endemic to the south-east Asian island of Borneo...
, crab-eating macaque
Crab-eating Macaque
The Crab-eating macaque is a cercopithecine primate native to Southeast Asia. It is also called the "long-tailed macaque", and is referred to as the "cynomolgus monkey" in laboratories.-Etymology:...
, and Rhesus macaque
Rhesus Macaque
The Rhesus macaque , also called the Rhesus monkey, is one of the best-known species of Old World monkeys. It is listed as Least Concern in the IUCN Red List of Threatened Species in view of its wide distribution, presumed large population, and its tolerance of a broad range of habitats...
swim regularly.
Large primates other than humans generally do not like to swim. Wild chimpanzees and some gorillas will wade in very shallow water but will make no attempt to cross larger bodies of water. Orangutans don't swim instinctively but will attempt it under pressure or if learned.
Among invertebrates, a number of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
species have adaptations for aquatic life and locomotion. Examples of aquatic insects
Aquatic insects
Aquatic insects live some portion of their life cycle in the water. They feed in the same ways as other insects. Some diving insects, such as predatory diving beetles, can hunt for food underwater where land-living insects cannot compete.-Breathing:...
include dragonfly
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...
larvae, water boatmen, and diving beetles. There are also aquatic spiders
Diving bell spider
The diving bell spider or water spider, Argyroneta aquatica, is the only species of spider known to live entirely under water.Argyroneta aquatica is found in northern and central Europe and northern Asia up to latitude 62°N. It is the only spider known to spend its whole life under water...
, although they tend to prefer other modes of locomotion under water than swimming proper.
Human swimming
Swimming has been known amongst humans since prehistoric times; the earliest record of swimming dates back to Stone AgeStone Age
The Stone Age is a broad prehistoric period, lasting about 2.5 million years , during which humans and their predecessor species in the genus Homo, as well as the earlier partly contemporary genera Australopithecus and Paranthropus, widely used exclusively stone as their hard material in the...
paintings from around 7,000 years ago. Competitive swimming started in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
around 1800 and was part of the first modern 1896 Summer Olympics
1896 Summer Olympics
The 1896 Summer Olympics, officially known as the Games of the I Olympiad, was a multi-sport event celebrated in Athens, Greece, from April 6 to April 15, 1896. It was the first international Olympic Games held in the Modern era...
in Athens
Athens
Athens , is the capital and largest city of Greece. Athens dominates the Attica region and is one of the world's oldest cities, as its recorded history spans around 3,400 years. Classical Athens was a powerful city-state...
, though not in a form comparable to the contemporary events. It was not until 1908 that regulations were implemented by the International Swimming Federation
Fina
Fina may refer to:*Fina, a character in the Skies of Arcadia video game*FINA, the International Swimming Federation*FINA, the North American Forum on Integration...
to produce competitive swimming
Swimming (sport)
Swimming is a sport governed by the Fédération Internationale de Natation .-History: Competitive swimming in Europe began around 1800 BCE, mostly in the form of the freestyle. In 1873 Steve Bowyer introduced the trudgen to Western swimming competitions, after copying the front crawl used by Native...
.