Research conducted in Bimini in The Bahamas spanning（横跨） almost two decades shows that female lemon sharks that were born there returned 15 years later to give birth to their own young, confirming this behavior for the first time in sharks. The study began in 1995, and has resulted in the capture, tagging, and release of more than 2,000 baby sharks over the 19-year, ongoing¹ project. This article, published online on December 5 in the journal Molecular² Ecology, entitled, "Two decades of genetic³ profiling yields first evidence of natal⁴（出生的） philopatry（归家冲动） and long-term fidelity⁵ to parturition⁶（分娩，生产） sites in sharks," was a collaborative effort involving scientists from The Field Museum, Bimini Biological Field Station Foundation, University of Miami and Stony⁷ Brook⁸ University (SBU). Results suggest that local and international efforts can make a big difference in the struggle to recover the world's coastal⁹ shark populations. Sharks have been heavily exploited to supply the Asian restaurants and banquet halls with shark fins¹⁰, the main ingredient in a highly prized soup of great cultural significance but of no nutritive value.

 

"We used each shark's individual DNA¹¹ fingerprint¹² to construct a large family tree," explained Dr. Kevin Feldheim, the A. Watson Armour¹³ 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," Dr. Feldheim added.

 

Many researchers had speculated that female sharks have this ability to home back 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 maturity¹⁴. Many hundreds of student volunteers came to the Bahamas to help with the 19-year ongoing research effort to finally prove that the speculation¹⁵ was true.

 

"The lagoon¹⁶ in Bimini is almost like a lake," said project founder¹⁷ 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 countless¹⁸ hours in the field and laboratory, but we finally answered this long-standing question and many others with this paper."

 

Sharks live a long time and take many years to mature, which is one reason why they are extremely vulnerable to overfishing. Evidence that sharks utilize¹⁹ the same nursery areas across generations underscores the critical importance of preserving local nursery habitats and can provide strong input²⁰ in designating inshore marine²¹ reserves that would protect sharks of future generations. The fact that some sharks are tightly connected to certain places as opposed to being ocean wanderers also indicates that individual countries or cooperative groups of neighboring countries can take action themselves to protect sharks that are, in a sense, theirs.

 

The study's coauthor, Dr. Demian Chapman, assistant professor at the School of Marine and Atmospheric²² Sciences and assistant director for science at the Institute for Ocean Conservation Science at SBU, said he started out 17 years ago as a volunteer researcher at Bimini charged with catching²³ sharks for tagging.

 

"When we tagged the first baby sharks in Bimini, Bill Clinton was President of the United States," said Dr. Chapman. "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."

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