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5 marine animals you may not know migrate

4 minute read

The spectacle of animal migration is a fascinating topic, present in a range of species from mammals and birds to reptiles and fish.

In light of the recent ‘State of the World’s Migratory Species’ report, which detailed steep population declines, we highlight the beautiful diversity of migratory marine animals across the globe.

What are migratory species?

Migratory species move from one habitat to another, either alone or as part of a group in seasonal and predictable patterns. Different species migrate for various reasons, but it is often so they can search for food or find a suitable place to breed.

Here, we look at five species which you may not know also migrate across the globe.

Spider crab

Spider crab

Credit: Martin Stevens

Close to home, you will find the extraordinary annual migration of spider crabs.

In order to grow, spider crabs (like all crustaceans) must shed their hard outer shell – a process called moulting or ecdysis. This reveals a new soft shell which expands to let them grow, but leaves them vulnerable to predation whilst the new shell hardens.

In summer or early autumn, spider crabs may migrate into shallow waters around Wales and southwest England gathering in huge aggregations, sometimes in the thousands. They do this to gain safety in numbers during their moult. Later in the year, they migrate offshore to deeper waters. Spider crabs have been known to migrate over 100 miles, with each journey taking up to 3 months. These aggregations are being reported more frequently in the UK and may be a consequence of our warming oceans.

Once a female spider crab has moulted for the last time, they develop eggs. After the spider crabs migrate back to shallow waters, their eggs are fertilised during mating. These migratory behaviours and aggregations not only help to increase survival and reproductive success of spider crabs, but also contribute to maintaining a healthy and diverse ecosystem. Large piles of moulted shells are left behind after the moulting aggregations, which contributes to important nutrient transfer between shallow and deep waters.

Nassau grouper

N Grouper at cleaning station.JPG

Credit: David M. Stone

If you’ve ever found yourself wondering, do fish migrate? Well, the answer is yes - with fish accounting for over 50% of globally threatened or near threatened migratory species.

The Nassau grouper is a Caribbean coral reef fish that migrates over 200 km to seasonal spawning grounds. They tend to migrate once a year, with each journey taking up to three weeks, and this usually occurs near to the full moon periods of December, January, or February. Once they reach their destination, Nassau grouper will stay for 1-2 days, with thousands of them gathering specifically to spawn - a common reproductive strategy in reef fish species. However, due to the predictable nature of their migratory routes, these spawning grounds are now targets for unsustainable fishing, which greatly reduces their reproductive success and renders them critically endangered.

Grey-headed albatross

Grey-headed albatross

Credit: Graeme Cresswell

As migrating starlings arrive from the North over winter, spectacular murmurations can be seen around the UK's coasts. Many seabird species such as the grey-headed albatross also embark on migratory journeys away from their breeding grounds in sub-Antarctic islands. This solitary species can spend up to 16 months at sea, heading toward the Antarctic Polar Frontal Zone in search of food such as squid and krill.

This albatross has one of the lowest reproductive rates of any bird and is now endangered. This is largely due to bycatch from longline fisheries, but ingestion of plastic debris has recently been identified as another cause of mortality.

Humpback whale

Humpback Whale breaching Tonga Martin Prochazkacz

Credit: Martin Prochazkacz via Shutterstock

Found in seas across the world, this magnificent species migrates vast distances from their high-latitude feeding areas to mating grounds in low-latitude tropical waters.

Humpback whales spend time foraging in polar regions for prey such as krill, salmon, and herring. This allows them to build up blubber ahead of the winter, where they embark on a 6-8 week journey to their breeding grounds, where populations gather to mate and nurse.

The migratory route of humpback whales is one of the most impressive of all species, and humpback sightings are becoming increasingly common in UK waters. Just last month, crowds gathered off the coast of Falmouth to catch a glimpse of three humpbacks breaching.

Since restrictions on commercial whaling were introduced in 1986, humpback whale populations have shown signs of recovery. However, this rise in numbers is not always reflected at a local scale, with subpopulations in the Arabian sea still showing a steep decline due to entanglement in fishing nets and ship strikes. The recent expansion of the South Georgia & the South Sandwich Islands Marine Protected Area, part of the ‘humpback highway,’ is a crucial step toward protecting the migratory routes of whales returning to polar regions after mating season.

Manta ray

manta ray

Credit: Rohan Holt

Manta rays can be found in temperate, tropical, and subtropical waters all around the globe. Their migratory patterns are far less predictable than other species, instead corresponding with seasonal upwelling, shifting weather patterns, and the abundance of food sources such as plankton.

This majestic species is particularly at risk of incidental catch by fishing nets, and sadly suffers from high rates of post-release mortality. Their migratory route is part of the Eastern Tropical Pacific Marine Corridor, which is set to become part of the world’s largest transboundary Marine Protected Area. This intergovernmental initiative aims to conserve the biological diversity of the area, providing crucial protection for migratory species such as the hammerhead shark, green sea turtle, and manta ray, against human activities such as overfishing.

Why are migratory species important?

Overexploitation of marine resources, pollution, climate change and severe weather, are some of the greatest threats to migratory marine animals, with a shocking 97% of migratory fish species now threatened with extinction. Migratory species play a key role in maintaining a healthy and complex ecosystem, with their epic journeys helping to transfer nutrients across the globe. It is therefore crucial that we take action to protect and conserve areas frequented by animals on their migratory routes.

For further information, check out the state of the world’s migratory species report.

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