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Natal homing, or natal philopatry, is the homing process by which some adult animals that have migrated away from their juvenile habitats return back to their birthplace to reproduce. This process is primarily used by aquatic animals such as sea turtles and salmon, although some migratory birds and mammals also practice similar reproductive behaviors. Scientists believe that the main cues used by the animals are geomagnetic imprinting and olfactory cues. The benefits of returning to the precise location of an animal's birth may be largely associated with its safety and suitability as a breeding ground. When seabirds like the Atlantic puffin return to their natal breeding colony, which are mostly on islands, they are assured of a suitable climate and a sufficient lack of land-based predators.
Sea turtles born in any one area differ genetically from turtles born in other areas. The newly hatched young head out to sea and soon find suitable feeding grounds, and it has been shown that it is to these feeding areas that they return rather than to the actual beach on which they started life. Salmon start their lives in freshwater streams and eventually travel down-river and are washed out to sea. Their ability to travel back, several years later, to the river system in which they were spawned is thought to be linked to olfactory cues, the "taste" of the water. Atlantic bluefin tuna spawn on both the east and west shores of the Atlantic Ocean but intermingle as they feed in mid-ocean. Juvenile tuna that have been tagged have clearly shown that they almost invariably return to the side of the Atlantic on which they were spawned.
Various theories have been put forward as to how the animals find their way home. The geomagnetic imprinting hypothesis holds that they are imprinted with the unique magnetic field that exists in their natal area. This is a plausible theory but has not been proven to occur. Pacific salmon are known to be imprinted on the water chemistry of their home river, a fact that has been confirmed experimentally. They may use geomagnetic information to get close to the coast and then pick up the olfactory cues. Some animals may make navigational errors and end up in the wrong location. If they successfully breed in these new sites, the animal will have widened its breeding base which may ultimately increase the species' chances of survival. Other, unknown means of navigation may be involved, and further research is needed.
There are several different kinds of marine animals that demonstrate natal homing. The most commonly known is the sea turtle. Loggerhead sea turtles are thought to show two different types of homing. The first of which comes in the early stages of life. When first heading out to sea, the animals are carried out by tides and currents with little swimming involved. Recent studies now show that the animals demonstrate homing to feeding grounds near their natal birthplace.
Turtles of a specific natal beach show differences in their mitochondrial DNA haplotypes that distinguish them from turtles of other nesting areas. [1] Many turtles from the same beaches show up at the same feeding areas. Once reaching sexual maturity in the Atlantic Oceans, the female Loggerhead makes the long trip back to her natal beach to lay her eggs. The Loggerhead sea turtle in the North Atlantic cover more than 9,000 miles round trip to lay eggs on the North American shore.
The migration of North Pacific Salmon from the ocean to their freshwater spawning habitat is one of the most extreme migrations in the animal kingdom. The life cycle of a salmon begins in a freshwater stream or river that dumps into the ocean. [2] After spending four or five years in the ocean and reaching sexual maturity, many salmon return to the same streams they were born in to spawn. There are several hypotheses on how salmon are able to do this.
One hypothesis is that they use both chemical and geomagnetic cues that allow them to return to their birthplace. The Earth's magnetic field may help the fish navigate the ocean to find the spawning region. From there, the animal locates where the river dumps into the sea with the chemical cues unique to the fish's natal stream. [3]
Other hypotheses rely on the fact that salmon have an extremely strong sense of smell. One hypothesis states that salmon retain an imprint of the odor of their natal stream as they are migrating downstream. Using this memory of the odor, they are able to return to the same stream years later. Another smell-related hypothesis states that the young salmon release a pheromone as they migrate downstream, and are able to return the same stream years later by smelling the pheromone they released.
Atlantic bluefin tuna spawn on both the east and west shores of the Atlantic Ocean. When a bluefin tuna hatches, there is a chemical imprint in the animal's otoliths based on the water's chemical properties. Fish born in different regions will show clear differences here. Studies of the commercial fishing industry in the United States show that the population of bluefin tuna in the North Atlantic is made up of fish hailing from both coasts. While the fish may live in close proximity out in the Atlantic, they return to their natal region to spawn. Electronic tagging done over several years showed that 95.8 percent of the yearlings tagged in the Mediterranean Sea returned there to spawn. Results for the Gulf of Mexico were 99.3 percent. [4] With the overfishing of this species, scientists have much to learn about their spawning habits in order to sustain the population for both a reliable food source and a healthy ecosystem.
Atlantic puffins spend the winter at sea and then return to the places of their birth, as has been shown by ringing birds. The breeding sites are usually inhospitable clifftops and uninhabited islands. Birds that were removed as chicks and released elsewhere were found to show fidelity to their point of liberation rather than to their birthplace. [5]
One idea about how animals accomplish natal homing is that they imprint on the unique magnetic field that exists in their natal area and then use this information to return years later. This idea is known as the "geomagnetic imprinting hypothesis" [6] The concept was developed in a 2008 paper that sought to explain how sea turtles and salmon can return to their home areas after migrating hundreds or thousands of kilometers away [7]
In animal behavior, the term "imprinting" refers to a special type of learning. Exact definitions of imprinting vary, but important aspects of the process include the following: (1) the learning occurs during a particular, critical period, usually early in the life of the animal; (2) the effects last a long time; and (3) the effects cannot be easily modified. [8] For natal homing, the concept is that animals like sea turtles and salmon imprint on the magnetic field of their home area when young, and then use this information to return years later.
Geomagnetic imprinting has not been proven to occur, but it appears to be plausible for several reasons. The earth's magnetic field varies across the globe in such a way that different geographic areas have different magnetic fields associated with them. [6] Also, sea turtles have a well-developed magnetic sense [9] and can detect both the intensity (strength) of the Earth's field as well as the inclination angle (angle at which the field lines intersect the earth's surface). [10] Thus, it is plausible that sea turtles, and maybe salmon also, can recognize their home areas using the distinctive magnetic fields that exist there.
Pacific salmon are known to imprint on the chemical signature of their home river. [11] This information helps salmon find their home river once they reach the coast from the open sea. In most cases, chemical cues from rivers are not thought to extend very far out into the ocean. Thus, salmon probably use two different navigational systems in sequence when they migrate from the open sea to their spawning grounds. [12] The first one, possibly based on the earth's magnetic field (see Geomagnetic Imprinting above), is used in the open ocean and probably brings salmon close to their home river. Once they are close to the home river, salmon can use olfactory (chemical) signals to find their spawning area.
Many of the classical studies demonstrating olfactory imprinting in salmon were carried out by Arthur Hasler and his colleagues. [13] In one particularly famous experiment, young salmon were imprinted with artificial chemicals and were released into the wild to perform their normal migrations. Almost all of the young fish returned to the same stream that had also been artificially imprinted with the same chemicals, proving that the fish do use chemical cues to return to their natal region.
Thermal pollution, which refers to the degradation of water quality by changing the ambient water temperature, has a serious effect on natal homing of chum salmon. Chum salmon is a typical cold water fish that prefer water around 10 °C (50 °F). When water temperature is raised due to thermal pollution, chum salmon tends to dive into deep water for thermoregulation. This reduces the time chum salmon spent in surface water column and reduce the chance for chum salmon to approach natal river since the chemical cue for natal homing is concentrated on surface water.
It has been studied and recorded by scientists that at a beach in eastern Mexico, where Kemp's ridley turtles nest, a navigational error from the inclination angle over a period of one decade would lead the turtles only within an average of 23 kilometres (14 mi) from their natal region. Other locations resulted in navigational errors of over one hundred kilometers in the same period of time. Results from this study show that the navigational tool of geomagnetic imprinting is believed to only navigate the marine animals close to where they were born and then the animals rely on chemical cues of the tributaries and rivers to direct them to back to their birthplace.
These navigational errors have actually strengthened the evolutionary trait of natal homing for marine animals by resulting in some animals straying from their birthplace. Most animals return to their natal region because they know it is a safe place to lay their eggs. These regions will usually have few predators, the correct temperature and climate, and will have the right type of sand for turtles because they cannot lay eggs in wet and muddy environments.
The few animals that do not return to their natal region and stray to other places to reproduce will provide the species with a variety of different locations of reproduction, so if the original natal locations have changed, the species will have expanded to more places and will ultimately increase the species' survival chances. [3]
Although scientists have been studying marine animals that perform natal homing for years, they are still not positive that geomagnetic imprinting and chemical cues are the only navigational tools they use for their incredible migrations. There is still much more research to be done until scientists can fully understand how these animals can travel such great distances to reproduce. Fortunately, as technology has progressed, there are several tools now available to scientists such as data loggers equipped with magnetometers that can easily be attached to the animals. Not only do they give data showing the animal relative to the Earth's magnetic field, but some also give latitude based on this, longitude based on light levels, temperature, depth, etc. Pop-up satellite archival tags are used to gather data and have the ability to transfer this data via Argos System satellites to the scientist.
Salmon is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic and North Pacific basin. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen.
Sea turtles, sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, Kemp's ridley, and olive ridley sea turtles. All of the seven species listed above, except for the flatback, are present in US waters, and are listed as endangered and/or threatened under the Endangered Species Act. The flatback itself exists in the waters of Australia, Papua New Guinea and Indonesia. Sea turtles can be categorized as hard-shelled (cheloniid) or leathery-shelled (dermochelyid). The only dermochelyid species of sea turtle is the leatherback.
Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear.
The Atlantic bluefin tuna is a species of tuna in the family Scombridae. It is variously known as the northern bluefin tuna, giant bluefin tuna [for individuals exceeding 150 kg (330 lb)], and formerly as the tunny.
A salmon run is an annual fish migration event where many salmonid species, which are typically hatched in fresh water and live most of the adult life downstream in the ocean, swim back against the stream to the upper reaches of rivers to spawn on the gravel beds of small creeks. After spawning, all species of Pacific salmon and most Atlantic salmon die, and the salmon life cycle starts over again with the new generation of hatchlings.
Steelhead, or occasionally steelhead trout, is the common name of the anadromous form of the coastal rainbow trout (Oncorhynchus mykiss irideus) or Columbia River redband trout. Steelhead are native to cold-water tributaries of the Pacific basin in Northeast Asia and North America. Like other sea-run (anadromous) trout and salmon, steelhead spawn in freshwater, smolts migrate to the ocean to forage for several years and adults return to their natal streams to spawn. Steelhead are iteroparous, although survival is approximately 10–20%.
The Atlantic salmon is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are found in the northern Atlantic Ocean and in rivers that flow into it. Most populations are anadromous, hatching in streams and rivers but moving out to sea as they grow where they mature, after which the adults seasonally move upstream again to spawn.
Magnetoreception is a sense which allows an organism to detect the Earth's magnetic field. Animals with this sense include some arthropods, molluscs, and vertebrates. The sense is mainly used for orientation and navigation, but it may help some animals to form regional maps. Experiments on migratory birds provide evidence that they make use of a cryptochrome protein in the eye, relying on the quantum radical pair mechanism to perceive magnetic fields. This effect is extremely sensitive to weak magnetic fields, and readily disturbed by radio-frequency interference, unlike a conventional iron compass.
The green sea turtle, also known as the green turtle, black (sea) turtle or Pacific green turtle, is a species of large sea turtle of the family Cheloniidae. It is the only species in the genus Chelonia. Its range extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans, but it is also found in the Indian Ocean. The common name refers to the usually green fat found beneath its carapace, not to the color of its carapace, which is olive to black.
Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs.
The southern bluefin tuna is a tuna of the family Scombridae found in open southern Hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to 2.5 metres and weighing up to 260 kilograms (570 lb), it is among the larger bony fishes.
Animal migration is the relatively long-distance movement of individual animals, usually on a seasonal basis. It is the most common form of migration in ecology. It is found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The cause of migration may be local climate, local availability of food, the season of the year or for mating.
The Pacific bluefin tuna is a predatory species of tuna found widely in the northern Pacific Ocean, but it is migratory and also recorded as a visitor to the south Pacific.
Homing is the inherent ability of an animal to navigate towards an original location through unfamiliar areas. This location may be either a home territory, or a breeding spot.
Pop-up satellite archival tags (PSATs) are used to track movements of marine animals. A PSAT is an archival tag that is equipped with a means to transmit the collected data via the Argos satellite system. Though the data are physically stored on the tag, its major advantage is that it does not have to be physically retrieved like an archival tag for the data to be available making it a viable, fishery independent tool for animal behavior and migration studies. They have been used to track movements of ocean sunfish, marlin, blue sharks, bluefin tuna, swordfish and sea turtles to name a few species. Location, depth, temperature, oxygen levels, and body movement data are used to answer questions about migratory patterns, seasonal feeding movements, daily habits, and survival after catch and release, for examples.
Olfactory navigation is a hypothesis that proposes the usage of the sense of smell by pigeons, in particular the mail pigeon, in navigation and homing.
Sea turtle migration is the long-distance movements of sea turtles notably the long-distance movement of adults to their breeding beaches, but also the offshore migration of hatchings. Sea turtle hatchings emerge from underground nests and crawl across the beach towards the sea. They then maintain an offshore heading until they reach the open sea. The feeding and nesting sites of adult sea turtles are often distantly separated meaning some must migrate hundreds or even thousands of kilometres.
Animal navigation is the ability of many animals to find their way accurately without maps or instruments. Birds such as the Arctic tern, insects such as the monarch butterfly and fish such as the salmon regularly migrate thousands of miles to and from their breeding grounds, and many other species navigate effectively over shorter distances.
Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's. Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey. Sharks can sense frequencies in the range of 25 to 50 Hz through their lateral line.
The olfactory system is the system related to the sense of smell (olfaction). Many fish activities are dependent on olfaction, such as: mating, discriminating kin, avoiding predators, locating food, contaminant avoidance, imprinting and homing. These activities are referred to as “olfactory-mediated.” Impairment of the olfactory system threatens survival and has been used as an ecologically relevant sub-lethal toxicological endpoint for fish within studies. Olfactory information is received by sensory neurons, like the olfactory nerve, that are in a covered cavity separated from the aquatic environment by mucus. Since they are in almost direct contact with the surrounding environment, these neurons are vulnerable to environmental changes. Fish can detect natural chemical cues in aquatic environments at concentrations as low as parts per billion (ppb) or parts per trillion (ppt).