Birds, buffalo, and butterflies are famous for their migratory habits. These are typically driven by the weather and can embark on phenomenal long-distance pilgrimages that literally span continents.
In the ocean, there are similar migratory patterns. Humpbacks can travel 5000 miles between warm and cold waters.
But what about sharks; do they migrate?
In terms of migration, sharks can be divided into local and migratory species. Local species mostly stay put, choosing to venture no more than about 100 miles from their homes. Migratory sharks such as the great white can cover 2500 miles between feeding grounds.
But there are other forms of migration to consider. Migrating across the ocean is one thing, but when you include movement between deep and shallow waters, you get a whole new category of migration, and this can include a lot of the so-called local sharks.
So, it seems that migration is particularly common in sharks, in one direction or another. Let’s take a more comprehensive look at migration in sharks.
Do all sharks migrate?
More than 80% of marine life migrates!
We’ve mentioned local sharks sticking within about 100 miles of their location, so we know not all sharks migrate across the ocean, but in water, there are three axes: forward/backward (North or South), right to left (East and West), and up and down.
When an animal moves between shallow and deep waters, it’s called vertical migration. This occurs in several ‘local’ shark species.
There are other types of migration too, and most sharks fall into one or more of these migratory categories.
Here are the different types of migration in more detail:
When a fish moves between fresh and saltwater, as is the case with the unusually resilient bull shark, this migration pattern is called Diadromousmigration.
Animals who do this usually do it during spawning season, and it’s a way of laying their eggs or giving birth in the safety of different habitats, away from natural predators.
For the nerds like me, there are two types of Diadromous migration:
- Going from freshwater to saltwater is called Anadromous migration and
- going from saltwater to freshwater is called Catadromousmigration.
When sharks are moving within their ocean habitat looking for food or breeding grounds, this is called Oceanodromous migration.
Sharks migrating from North to South, or vice-versa are performing Latitudinalmigrations, which is usually related to the climate.
Like birds, they will often leave their habitat during the winter, have a summer vacation in tropical waters, and then head back to work when the weather is better. Hammerhead sharks and mako sharks migrate latitudinally.
When the migration is across longitudinal lines, East to West, or vice-versa, this is known as Longitudinalmigration.
Note: These terms might feel counter-intuitive; latitude spans West to East, so it seems like that type of migration should be the definition of Latitudinal migration. But think of it instead as crossing latitudinal lines. To do this, you have to travel North to South or vice versa.
The same logic then applies to Longitudinal migration!
In sharks, and really in most migratory animals, longitudinal and latitudinal migration patterns are common together. For example, the great white’s trip from New York to South Africa covers both longitudinal and latitudinal lines.
Sharks who mostly stay put may take part in verticalmigrations daily. This is when they come up from the murky depths to feed or spawn and then return. It can also be the other way around.
Throughout the day, plankton – the foundation of the food web – move up and down in the water column, and this migration brings with it the chain of other animals that predate upon them. It’s thought that whale sharks and blue sharks do this.
Shoreward migration is typically the movement from water onto lands, such as in crabs or other marine animals capable of breathing air. But in some cases, it can be used to describe the migration from deeper waters into the shallows, for example, in the spiny dogfish, which seeks out shallow waters for breeding.
Not all sharks migrate, and some of the species that once did, have recently begun to do so less as climate change increases the temperature of the water.
As the East coast of the US hits record temperatures almost every year, blacktip reef sharks are staying where it’s comfortable.
On the other hand, some sharks are migrating even farther due to the change in the climate.
So, do all sharks migrate?
Almost all sharks will have some form of migration. Some travel long distances from tropics to temperate regions, seasonally. Some sharks stay in one location but dive and resurface on a daily cycle. Some even migrate up into rivers.
Where do sharks migrate to?
There’s no single place that sharks migrate to – their habits are determined by ecological factors such as feeding and breeding locations, as well as predators and competition.
As we’ve seen, some sharks migrate long distances; some just move up and down. And several sharks do both.
Here are a few examples of where sharks are going during their migrations:
- The bigeye thresher shark occupies both open water and shallow coastal areas. They’ve been shown to move up and down in the water column on a daily cycle. This diel vertical migration is pretty common, and these patterns can, unfortunately, overlap with the long-line fishing gear of commercial fishing, causing devastation to shark populations.
- Male and female Port Jackson sharks like to return to the area of their birth. Staying or returning to an animal’s birthplace is called philopatry (the most famous example of this is in salmon). The males and the females in Port Jackson sharks have been shown to diverge in their route and make their own way back, meeting at the destination after some valuable alone time.
- Great white sharks are well known for their extensive latitudinal migrations, but their vertical migratory patterns are harder to study. Using special tags placed on white sharks, scientists are able to measure the time-at-depth and the location of these sharks. Data is still pretty thin on the habits of great whites, but they seem to have complex diving patterns based on time of day, sex, and location.
- Similarly, by tagging 69 hammerheads, researchers were able to identify exactly which shark was where and spotted several who traveled hundreds of miles around their local island habitat. This behavior was quite uncommon, but it goes to show there are no set rules with sharks!
- Whale sharks already hold the record for largest shark and largest fish! Now it seems like they’re pushing for the record of longest migration. They’ve been recorded migrating more than 12000 miles and 6000ft deep. The strange thing is, we still don’t know exactly why!
(If you’re thinking of becoming a marine biologist, please consider contributing to the body of knowledge on these incredible animals. They are inquisitive and intelligent, and we could learn so much from them!)
Why do sharks migrate?
Typically, the motivations for any animal are simple. Food, sex, and fear. If a behavior can’t be explained by one of these motivations, chances are it will be one or both of the other two.
When sharks migrate, it’s often for chasing a favorable water temperature. Seasonal migrations occur in sharks for the same reasons as they do in birds: staying away from the cold winter weather. These migrations can be vast – up to 12000 miles – or they can be more localized – within 100 miles.
Other forms of migration occur because sharks need a safe place to breed.
In bull sharks, migration is into brackish or freshwater. These sharks choose to hide their young in the relative safety of these waters because other shark species and large ocean predators can’t tolerate the condition in this habitat.
Mating is another reason to migrate. Sharks need to hook up somewhere safe and comfortable, where all the eligible singles will gather. These vast breeding grounds are a popular way to reproduce in certain species, such as the nurse shark, and are also driven by changes in temperature.
When temperatures and light cycles change, so does the location of the food. In the daytime, many zooplankton sinks down into the darkness of the deep water to return at night. This migration brings with it many of the animals that feed on the zooplankton, and in turn, many of the animals that feed on them! Sharks exhibit diel vertical migration primarily for this reason, but in some cases, it’s also thought to be a way to shed parasites in the cold water of the deep.
Because temperature affects migratory patterns, climate change is one of the most significant factors now affecting seasonal migrations.
Tiger sharks are now migrating farther North than ever before, potentially impacting the local ecology in permanent ways.
Other species are migrating less often for the same reason: their food sources are now accessible year-round due to increases in water temperature.
Climate change is not a single mechanism. Global warming is one factor, but increases in ocean acidity due to the increase in CO2 in the atmosphere affects the range and prevalence of many of the tiny crustaceans that make up the planktonic foundation of the food web in the ocean.
White sharks are known to leave a feeding ground when killer whales enter it. Killer whales, or orca, hunt great whites for their fatty livers and are so feared by the white sharks that the sharks may abandon their hunting in that area for up to a year when the Orcas pass through.
When do sharks migrate?
The migration patterns of sharks follow a particular schedule depending on the reason for the migration.
In Diel vertical migration, it’s a daily cycle: the sharks enter the depths at dawn and return in the evening. This schedule is based on the light cycle in zooplankton and is probably related to the zooplankton cycle in sharks. Diel migration in threshers follows this pattern.
In long-distance migratory sharks, the season determines when they’ll migrate.
In that case, what season do sharks migrate?
As Northern waters cool in the Winter, sharks may leave the rich feeding grounds and head to warmer waters. Great whites are known for traveling between North American temperate water and South African tropical waters on a seasonal basis.
When breeding is responsible for the migration, the pattern is usually a combination of weather and birthing cycles.
Most animals give birth seasonally, which allows them to protect their young from the harshest weather patterns.
Bull sharks and Hammerheads return to shallow waters for spawning and giving birth.
Shark migrations occur in most species, in one form or another. They can be vast, globe-trotting pilgrimages or local daily commutes.
Almost all migration is driven by the temperature of the water, whether it’s for breeding, staying warm, or following food sources.
Because of this, climate change is now affecting the migratory patterns of sharks. Some are less inclined to leave in the winter because it isn’t getting as cold, and others are taking advantage of the warmth to travel even farther North in the Summer.
For example, the East Coast US waters are increasing in temperature faster than 99% of the rest of the world’s oceans, leading to an increase of many types of fish that are choosing to stay in the area rather than migrate to warmer waters. It’s hard to say what effect this will have on the oceans, but with apex predators entering an area, there is always a cascade of ecological effects.