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Unlock This CourseImagine swimming thousands of kilometres across the ocean without a map, GPS, or compass - yet somehow knowing exactly where you're going! This is what many marine animals do every year through long-distance horizontal migration. These incredible journeys are some of nature's most remarkable achievements, with animals travelling between feeding and breeding grounds across entire ocean basins.
Long-distance horizontal migration is different from vertical migration (moving up and down in the water column). Instead, it involves travelling vast distances across the ocean's surface, often following ancient routes that have been used for millions of years.
Key Definitions:
Marine animals migrate for several key reasons: to find the best feeding areas when food is abundant, to reach safe breeding grounds with ideal conditions for raising young, to escape harsh seasonal conditions and to avoid predators. These journeys are timed perfectly with seasonal changes in ocean conditions.
How do marine animals find their way across thousands of kilometres of seemingly empty ocean? Scientists have discovered that marine migrants use multiple navigation methods, often combining several techniques to stay on course.
Marine animals have evolved sophisticated navigation systems that put our technology to shame. They use a combination of internal compasses, environmental cues and even social learning to find their way.
Many marine animals can sense Earth's magnetic field using special cells containing magnetite crystals. This acts like an internal compass, helping them maintain direction even in the open ocean.
Some species use the sun, moon and stars as navigation aids. They can detect polarised light patterns in the sky that remain consistent even on cloudy days.
Ocean currents carry distinctive chemical signatures from different regions. Animals can "taste" the water to identify their location and follow familiar scent trails.
The ocean is home to some of the world's greatest travellers. These marine migrants cover distances that would challenge even modern transport systems, all powered by their own bodies and guided by instinct.
Arctic terns hold the record for the longest migration of any animal on Earth. These seabirds travel roughly 70,900 kilometres annually, flying from Arctic breeding grounds to Antarctic feeding areas and back. During their 30-year lifespan, they travel the equivalent of three round trips to the moon! They experience two summers each year and see more daylight than any other creature on the planet.
Whales undertake some of the most impressive migrations in the marine world. These gentle giants travel between polar feeding grounds rich in krill and warmer tropical waters perfect for breeding and giving birth.
Humpback whales migrate up to 25,000 kilometres annually - the longest migration of any mammal. They feed in polar waters during summer, building up blubber reserves, then travel to tropical waters to breed and give birth in winter. Mothers fast for up to 8 months during this journey!
Sea turtles are legendary navigators, with some species travelling over 10,000 kilometres between feeding and nesting beaches. What makes their story even more remarkable is that they return to the exact beach where they were born to lay their own eggs.
Young loggerheads ride ocean currents in the North Atlantic, taking 10-30 years to complete a circular journey of thousands of kilometres before returning to nest.
Baby turtles imprint on the magnetic signature of their birth beach, creating a magnetic "map" they use decades later to return home.
Turtles can sense water temperature differences as small as 0.1°C, helping them follow warm currents and find optimal nesting conditions.
Many fish species undertake spectacular migrations, often following seasonal changes in food availability and water temperature. These movements can involve millions of individuals and support entire fishing industries.
Atlantic bluefin tuna are the Formula 1 cars of the ocean, capable of swimming at speeds up to 70 km/h. These magnificent fish migrate across the entire Atlantic Ocean, travelling from feeding grounds off North America to spawning areas in the Mediterranean Sea. They can dive to depths of 1,000 metres and regulate their body temperature, allowing them to hunt in both warm and cold waters. Unfortunately, overfishing has severely reduced their populations.
Salmon migrations are among the most famous in the natural world. These fish are anadromous, meaning they're born in freshwater, migrate to the ocean to grow and mature, then return to their birth streams to spawn.
Pacific salmon can travel over 3,000 kilometres in the ocean before returning to spawn. They use their sense of smell to identify their home stream, remembering the unique chemical signature from when they were young. After spawning, Pacific salmon die, providing nutrients that feed the entire ecosystem.
Modern human activities pose serious threats to marine migration routes. Understanding these challenges is crucial for protecting these incredible journeys for future generations.
As human activity in the oceans increases, migrating marine animals face new and growing challenges that their ancient navigation systems weren't designed to handle.
Busy shipping lanes cross major migration routes, leading to ship strikes that can injure or kill large marine animals like whales. Noise pollution from ships also interferes with animal communication.
Changing ocean temperatures and currents are shifting food sources and disrupting traditional migration timing. Some species are arriving at breeding or feeding grounds when conditions are no longer optimal.
Plastic pollution, chemical runoff and oil spills contaminate migration routes. Marine animals can mistake plastic for food or become entangled in fishing gear.
Protecting marine migration routes requires international cooperation, as these journeys cross multiple countries' waters and international boundaries.
Countries are establishing marine protected areas along critical migration routes, providing safe corridors for travelling animals. These areas restrict fishing and shipping activities during peak migration periods, giving animals the space they need to complete their journeys safely.
Gray whales were once hunted nearly to extinction, with only a few hundred individuals remaining in the 1940s. Thanks to protection under international law and the establishment of protected areas along their migration route between Alaska and Mexico, gray whale populations have recovered to over 20,000 individuals. This shows that with proper protection, marine migration can be preserved.