Sharks Go Home To Give Birth
December 5, 2013

Sharks Head Back Home To Give Birth, Says 20-Year Study

[ Watch The Video: Lemon Shark Giving Birth ]

Lee Rannals for - Your Universe Online

New findings published in the journal Molecular Ecology shows that sharks head back to their origins to give birth. Salmon and sea turtles are known to head back to their birthplace in order to lay eggs, but this is the first time that scientists have confirmed that sharks do the same. These findings could have a big impact on local shark conservation efforts.

Researchers conducted a study in Bimini in The Bahamas for almost two decades, following female lemon sharks. They watched as the sharks returned there 15 years later to give birth to their own young, confirming this behavior for the first time in sharks.

"We used each shark's individual DNA fingerprint to construct a large family tree," said Dr. Kevin Feldheim, the A. Watson Armour III Manager of the Pritzker Laboratory for Molecular Systematics and Evolution at The Field Museum and the lead author of the study.

"We found that newborn sharks captured in the mid-1990s left the safety of the islands when they were between five and eight years old. Yet, despite leaving and visiting many other islands in their travels, these sharks 'remember' where they were born after a decade of roving, and are able to find the island again when they are pregnant and ready to give birth.”

Scientists have speculated that female sharks head back home to their birthplace to give birth, but it had never been proven, because it is very difficult to keep track of sharks from birth to maturity. The team had to utilize hundreds of student volunteers to help the with 19-year study to finally prove that their suspicions were true.

"The lagoon in Bimini is almost like a lake," said project founder Dr. Samuel Gruber, president and director of the Bimini Biological Field Station Foundation. "I realized that we had a chance to capture nearly every shark born into the lagoon each year, and this gave us the unique opportunity to see if the females actually come back to give birth.

However, it took us nearly two decades and countless hours in the field and laboratory, but we finally answered this long-standing question and many others with this paper."

Sharks have a long lifespan and take many years to mature, making it difficult to keep track of breeding and spawning behavior.

"When we tagged the first baby sharks in Bimini, Bill Clinton was President of the United States," said Dr. Demian Chapman, assistant professor at the School of Marine and Atmospheric Sciences. "When they started to mature and return to give birth, Barack Obama was President. If you think of all that has happened in the world over that period, just consider that is the amount of time it takes for many large sharks to reach maturity."

The findings highlight the critical importance of preserving local nursery habitats and can provide strong input in designating inshore marine reserves that would protect sharks of future generations. The results indicate that individual countries or cooperative groups of neighboring countries can take action themselves to protect sharks that are theirs.

The Bahamas recently enacted a law to fully protect all sharks in its waters, which will help sustain the annual $80 million shark tourism industry.