Mother Sharks Return Home to Give Birth


Shark moms go home — to the place where they were born — to give birth to their own young, a lengthy study has found.

The study, published in the latest issue of the journal Molecular Ecology, took nearly two decades to complete. It found that shark mothers, like salmon and sea turtle moms, believe there’s no place like home for giving birth.

The researchers focused on lemon sharks, but the findings likely apply to many other species. These particular lemon sharks live off the island Bimini in The Bahamas.

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Kevin Feldheim, manager of the Pritzker Laboratory for Molecular Systematics and Evolution at The Field Museum, led the study. In 1995, he and his colleagues captured, tagged and released more than 2,000 baby lemon sharks.

“We used each shark’s individual DNA fingerprint to construct a large family tree,” Feldheim explained in a press release.

“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.”

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Many other scientists had speculated that lemon sharks and other shark species had this ability, but the researchers could never prove it until now due to difficulties tracking sharks from birth to maturity. Bimini, though, provided an ideal spot to test out the theory.

“The lagoon in Bimini is almost like a lake,” said project founder 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.”

Now, conservationists have a better idea where to designate inshore marine reserves. Sharks aren’t just rogue ocean wanderers. They, and especially females, have a strong sense of home that stays with them throughout their entire lives.

“When we tagged the first baby sharks in Bimini, Bill Clinton was President of the United States,” said co-author Demian Chapman of Stony Brook University. “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.”

(Image: Matt Potenski)

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