Many marine animals undertake migrations over thousands of kilometres every year, often returning to the place of their birth to breed, or known food sources. Humpback whales have been recorded only altering their trajectory from previous migrations by a staggering 0.4 degrees. The question is: How do they know where they are going?

The answer is not simple unfortunately; little is known about this phenomenon, and navigation methods can vary from one species to another. It is believed the animals use a combination of different cues such as the Earth’s magnetic field and the sun. For those species that have sonar, they can “map” their environment, and for many species that migrate in groups it is also possible that the veterans lead the way, passing the rituals on through the generations. Although there are not many visual cues, things like water pressure will indicate depth, changes in chemical composition of the water can indicate for example where there are estuaries, sound and electrical currents travels better through water than air, and perhaps even the presence of other animals can indicate where or how far through their migration our pelagic friends have progressed.

Marine creatures migrate between countries, through some areas that are protected and through some that are not. This presents challenges for their protection, and necessitates increased collaboration between governments and conservation organisations

Whales

The longest migration on record was by a grey whale, clocking up a 13,987 mile (22,510 km) journey from Russia to Mexico and back.

The Sardine Run

Sardines can’t tolerate temperatures higher than 21 degrees Celsius so spawn then migrate to cooler climes.

Leatherback Turtles

Upon hatching, male leatherbacks spend the rest of their lives at sea; the females migrate back to the tropics to lay their eggs.

Bluefin Tuna

Bluefin tuna migrate several times a year between the US East Coast and the West Coast of Europe in search of food, a round trip of over 10,000 miles (16,100 km).

Golden Cownose Rays

These rays migrate in groups of around 10,000, appearing to change the water surface colour to gold.

Bullsharks

These sharks have an unusual migration pattern because they move from fresh water where they give birth to
salt water.

Read the rest of this article in No. 88 Issue 7/2016 of Scuba Diver magazine by subscribing here or check out all of our publications here.

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