Migration is one of the great mysteries of the animal kingdom that continue to elude scientists worldwide. While this phenomenon is witnessed in all major animal groups, including birds, mammals, insects, crustaceans, fish, reptiles and amphibians, surprisingly little definitive knowledge is understood about its mechanisms and specifics.  Broadly, migration refers to the large scale movement of an animal group from one place to another.  However, the reasons or triggers for such movements are varied; including seasonal changes in weather patterns and food availability to breeding behaviour. There is even something called irruptive migrations within certain species, which are migrations that don’t display any discernable pattern or reason for animal movements.   Migration can include species or individuals that must migrate, called obligate migrations, or can include facultative migration, where there is a choice to migrate or not. Migration can vary further between sex and age within a population and can be large or small scale. Some species, for example, caribou in Northern America or wildebeest and zebra in East Africa, migrate many thousands or kilometres, while others, like many crustaceans, migrate only a few hundred meters.

It’s difficult enough trying to understand terrestrial animal mass movements or migration patterns, so imagine trying to get a grasp on aquatic species!  The quest to understand worldwide shark migrations patterns has been a daunting task, even more so with such a notoriously difficult subject to study as the great white shark. Great white sharks used to be regarded as predominantly coastal territorial predators, staying close to shore where their main food source, seals and sea lions, were most prominent. However, with the advent of new satellite and electronic tagging technologies available, recent studies have started to prove otherwise. A study in 2002 tracked an individual tagged in Central California thousands of kilometres to the warm water of the Hawaiian Island chain. Read all about it here: http://news.stanford.edu/news/2002/january9/sharks-19.html

In South Africa, great white sharks in False Bay do not stay at Seal Island year-round although their food sources, cape fur seals, live at the island year round. In 2004 a great white shark tagged in Gansbaai migrated 11,000 km to Western Australia.  This is not a unique event; there have also been a few other recorded incidents of great whites from South Africa migrating to Australia and back within a year. Other individuals have been found to just migrate shorter distances, to other parts of South Africa or Namibia or in some cases just in shore within False Bay. Why do the sharks leave their food source in False Bay? Where do they go? Why do some swim so far and others not? Seasonal feeding patterns and mating behaviour have been put forth as theories for such unpredictable and varying behaviour but nothing has been proven. The amount we still have to learn and understand is staggering.

The reality is no matter how much we know, the animal kingdom continues to elude scientists.  Perhaps we will discover more about why great white sharks do what they do and perhaps we won’t.  What we can count on is that they are fascinating creatures that continue to pull at our imagination.

 

Allie Skidmore