• Claire Wang

Ocean Migrations

Due to the ocean’s ability to change conditions throughout the year, many ocean creatures must be able to move to different environments at different times of the year for a more suitable habitat. In other words, they need to migrate. Ocean animals migrate far more than land animals, with about 80% of all them migrating.

Above: the manta ray migration



Why do animals migrate?

There are many reasons for migrating, but most of them are due to another area having better conditions. These conditions can include more food resources, a more comfortable temperature, a place to breed and raise offspring, and an escape from predators. Animals that migrate have an advantage because they can “choose” which habitat they want to live in at a certain part of the year.


Ocean migrations are very common because they are the most efficient. They require less energy than running, as some land animals do, and they are also able to move fast because of ocean currents pushing them along the way. Animals who are able to fly also use more energy and resources along the way compared to ocean creatures. However, they are still more efficient than land migrations because animals who fly are generally lighter and faster.



General facts about ocean migrations

  • Cold water has more nutrients than warm water, so when animals go towards the north/south poles, it is generally due to feeding grounds being located in colder waters

  • Warm waters are better suited to raising offspring; that is why many animals go to the equator to raise them

  • Whales often migrate from the poles to the equator for the two reasons stated above

  • There are two phases of migrations: locomotion and fuel disposition. Locomotion is when the animal is actively traveling. Fuel disposition is when the animal is restoring their energy by eating. This can occur throughout the journey, at the beginning, at the end, or both.

  • Scientists aren’t sure about how animals are able to orient themselves and travel the same route every year, but some think that they may use the Earth’s magnetic field. Other guesses include using astronomical cues.



Below are some notable marine animal migrations, such as the migrations of the north pacific gray whale and sea turtles.




The North Pacific Gray Whale

This whale is thought to have the longest migration of any mammal. Gray whales journey from the south of Mexico, their breeding grounds, to the arctic ocean, where they feed. Mothers give birth to baby whales around January, and they travel in pairs together. Female whales without calves and grown up male whales tend to travel faster. Eventually, all of them swim along the California coastline, up to Oregon and Washington, cross to Canada, and continue swimming along Alaska’s coastline until they reach the Arctic ocean.


Above: The gray whale



Gray whales can finish their journey any time between May to June. However, arriving too early has its consequences since it takes time for ice to melt, and if they are too early, a lot of ice will be frozen, blocking them from breathing.


The Arctic is their feeding ground because it has more nutrients. In general, cold water has more nutrients than warm water.



The sea turtle migration

Another notable journey is one that sea turtles take. Though not all species of sea turtles take the same route, their migrations have many similarities.


A sea turtle’s journey begins when it is born on a beach. It has to dig its way out of the hole its mother dug, and then scamper down to the water. Sea turtles know what direction the water is because they look for reflected moonlight on the surface. Unfortunately, artificial light from man made buildings can disorient hatchlings to go in the wrong direction. After entering the water, they immediately begin swimming to foraging areas. The first 24-36 hours of a sea turtle’s life are one of its most dangerous ones, as it is extremely vulnerable to predators. This period of time is also called the “frenzy period”, where the hatchlings swim non-stop for the entire time.



Above: the stages of a sea turtle's migration


Scientists believe that the hatchlings use the waves to determine which direction to go in. Because they want to travel along the coastline, they must make sure to travel perpendicular to the direction waves are pushing in. Scientists think that sea turtles have electroreceptors that help them orient themselves to the Earth’s magnetic field, just like sharks and rays. Another theory states that green sea turtles are able to use the position of the sun to determine where they are.


Sea turtles can have one designated foraging ground, multiple foraging grounds, or move randomly across the ocean to different foraging grounds with no sort of pattern (the leatherback sea turtle does this), but in the end, they are almost always able to return to the same beach they were born. Scientists are still not sure how turtles get their incredibly accurate navigational skills.



Sources:

https://www.neefusa.org/weather-and-climate/marine-species-move#:~:text=Did%20You%20Know%3F,times%20faster%20than%20land%20species.

https://journeynorth.org/tm/gwhale/MigrationRoute_Map2009.html

https://en.wikipedia.org/wiki/Sea_turtle_migration

https://www.sciencedirect.com/science/article/pii/S0960982218309357


Image sources:

http://www.storytrender.com/wp-content/uploads/2019/05/7_CATERS_RAY_MIGRATION_03-1024x683.jpg

https://i.natgeofe.com/n/e6cb0ee4-77c5-4181-bf6a-b79a28237e6c/gray-whale.jpg

https://lh3.googleusercontent.com/proxy/67ec38OJUwM0j3g8g83V1znEgNFYawcyC6ErTLLQtTjfyUdByC-9LVmzsTjpSjoNo81UvyeXXXdoTHLkL7Ww8KiX54VMuvGpV6WX




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