Sharks play an essential rol in the health of our oceans

Information, News, Research

No, sharks are NOT coming after us, they are just migrating as usual…

Migrating sharks along the Forida Coast, a seasonal event
Photo source: mypalmbeachpost.com

Whether sharks migrate or not depends to a large degree on temperature and seasonal changes, reproduction, and food sources.

Reproduction:

Sharks, like many other animals, migrate for purposes of mating and giving birth. These migrations are timed by seasons of the year, which cause water temperature changes that may trigger sharks to migrate to their breeding and pupping grounds. The sandbar shark, for example, is found in large numbers off the east coast of Florida, in spring, a mating ground for the shark. They go north in early summer, and females move into northeastern bays and estuaries in June to have their pups. Adult sandbar sharks will continue their migration northward after pupping season and will move south for the winter as water temperatures begin to cool.

Many sharks migrate along the shores of Florida each year, and have been doing so for a long, long time.

 

Great white sharks migration towards and from the shore regularly. That is a normal pattern, but to many people, it seems as if this is ‘new’: there is much more media attention, and there are many, many more people in the water than several decennia ago. For years, humans have thought of great white sharks wandering the sea at random, only occasionally venturing close to shore. But scientists spent eight years tracking the movements of 179 great white sharks and discovered that these predators have very predictable migration patterns between Hawaii and the North American coast. Dots below show approximate locations where 68 sharks tagged with satellite sensors were recorded at various times. This behaviour was observed before, and never was there so much scientific evidence through tagging and observation projects as there is now.

 

Migration patterns of great white sharks from the US to Hawaii

 

In South Africa, the great white sharks do not live in False Bay and Gansbaai permanently, but tagged sharks proved they the species moves to other parts of the globe with great efficiency.

Similar patterns have been observed in Australia and New Zealand.

 Food sources:

Another primary cause of animal migrations is availability of food sources. Movements of fish which sharks prey on will cause the sharks to follow in pursuit. Often, the movements of food fish are related to water temperature changes similar to those that factor in shark migrations. Seasonal availability of marine mammals also factors in migration patterns of those species of sharks that feed upon them.

Temperature and Seasonal Changes:

As seasons change, many species migrate in order to stay within their preferred water temperature range. Most sharks are cold-blooded (their internal body temperature is the same as the outside water temperature), so they will migrate to stay within their preferred temperature ranges. Some sharks prefer warm temperatures and will spend much of their time in tropical waters. Other sharks, such as the great white shark and the shortfin mako shark have a higher metabolic rate, which allows them to generate their own heat. These sharks have a wider range of movement, and are able to withstand lower water temperature ranges. Water temperature changes also affect the movements of fish and other food sources. Therefore, sharks may migrate to pursue food that prefers a certain temperature range. Through tagging and recapture research, scientists are able to associate different temperature ranges with different species of sharks, following their migrations from one location to another (source: Ocean of Knowledge).

But no matter how much we know, the ocean creatures continue to elude scientists. More research is needed to establish breeding and feeding ground to collect empiric evidence that can stimulate conservation in all the waters for all the species that cross national boundaries, so the whole habitat of endangered species can be protected. Otherwise, protection can be useless…

One of the organisations working on that, is the Convention Migratory Species, that listed the Great White Shark, Basking Shark, the Shortfin Mako Shark, Longfin mako, Porbeagle, Manta ray , the Whaleshark and the Spiny Dogfish.  But many more shark and ray species should be on this list!

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