Birds migrate tens of thousands of miles a year, gliding above water to find food, breed and escape cold weather. Marine animals however are unable to rely on tailwinds or altitude to get them where they need to go. So what skills do our friends with fins use to get around our watery planet?
Dolphins use echolocation to find their way in the ocean, as well as to identify prey in poor visibility or very deep water. This is the same system that bats use to communicate. Sound travels better in water than in air and like sonar, it is based entirely on sound waves. John Kassewitz, founder of the research organization Speak Dolphin describes it like this: “When a dolphin scans an object with its high-frequency sound beam, each short click captures a still image, similar to a camera taking photographs.”
While we can see chemical pollution, dolphins are under threat by noise pollution. Boat traffic, sonar and drilling can all affect their ability to use echolocation to communicate and navigate.
The award for longest ocean migration of any mammal goes to the Humpback whale. They cover 13670 miles each year when they leave summer feeding grounds near the poles to breed in warmer winter Equatorial waters. The longest known migration of a fish was by a female great white shark called "Nicole". She swam around 6900 miles from South Africa to western Australia, and back again in just nine months!
Many shark species – including Silvertip, hammerhead and Galápagos sharks - migrate in straight lines annually between Cocos, Galápagos, Malpelo and the Socorro Islands. They move between food-rich seamounts and this route has now become known as the Shark Highway. Scientists assume that the animals navigate by using a combination of the following:
- their noses (controlled by the olfactory bulbs in the brain)
- electro sensory organs located under the skin on the snout and along either side of the shark’s body called the lateral line
- Earth’s magnetic field
Thanks to satellite tagging we are now able to better understand how the world’s largest fish - the whale shark - moves around. In 2011 a whale shark named Anne was tagged at Coiba Island in Panama. She travelled over 12,516 miles from the Tropical Eastern Pacific to the western Indo-Pacific (Mariana Trench) in 841 days, primarily via the North Equatorial Current. Was it some tasty plankton she was heading for or to breed or give birth? Considering how big they are, whale sharks do have a tendency to disappear. They move away from coastal zone feeding areas for long periods, perhaps to avoid predation. It is also very rare to see juvenile whale sharks in the wild.
Most of us are aware that sea turtles return to the beach where they were born to lay their eggs. This is called natal homing and is a geomagnetic sense. Soon after hatching newborn turtles embark on huge oceanic migrations. They do have substantial help from the ocean currents, although turtle hatchlings can actively try to remain within favourable habitats. They stay in pelagic habitats for up to 15 years navigating by measuring the earth's magnetic field!
A loggerhead sea turtle named Yoshi that was released after 20 years in captivity swam 22,000 miles over two years. Kenneth Lohmann of the University of North Carolina has suggested that cues utilized by other migratory animals - such as the position of the sun or stars, polarized light, odours, wind direction, infrasound and/or the earth's geomagnetic field - may play a role in their navigation.
Chris Packam’s recent BBC series Animal Einstein’s revealed that dung beetles are capable of navigating via the Milky Way. A study in 2006 at the Marine Science Centre in Germany showed that Harbour Seals are also able to navigate using specific lodestars (guiding stars like the North or Pole star) to forage for food in the open ocean at night. They also use large whiskers, which can sense vibrations in water as their prey moves.
We humans are not biologically fitted with many of these systems nor are we smart enough to use such navigational techniques. See our range of compasses here on the Mike’s Dive Store website. Many dive computers today are also fitted with digital compasses to help us get from A to B, just not for a 22,000 mile journey as you will probably need to recharge your battery…..