ScienceShot: Mother Sharks Head Home to Give Birth

Matt Potenski

ScienceShot: Mother Sharks Head Home to Give Birth

After almost 2 decades of research, scientists have confirmed what they long suspected: Female lemon sharks (Negaprion brevirostris, pictured) swim back to where they were born when ready to give birth, even after years away. Lemon sharks, and possibly other shark species, such as blacktip reef sharks, are thus similar to salmon and sea turtles, which also return to their exact natal nurseries. To prove that pregnant sharks seek out their original home waters, scientists captured and tagged more than 2000 baby lemon sharks at Bimini, Bahamas, between 1995 and 2012. They also collected genetic samples from each shark pup, creating family trees that allowed them to connect newborns to specific mothers. Lemon sharks do not hatch from eggs, but emerge fully developed from their mothers after a yearlong pregnancy; eight to 12 pups are born in a litter. At Bimini, they linger in their nursery waters until about age 5, when they leave the island’s safety to rove. They reach sexual maturity around age 12. At least six of the female sharks the researchers tagged returned to the exact same waters where they were born 15 years earlier, they report online today in Molecular Ecology. Although that is not a large sample size, the researcher says it reflects the difficulty of capturing adult sharks—and the hazards shark face. Typically only one to three baby sharks in a litter survive beyond their third year. The researchers are not certain how the mothers are able to find their way home, but suspect that they imprint on the area during their early years. Knowing that sharks are tightly connected to specific places should help with conservation measures, the scientists say, especially efforts to preserve specific shark nurseries.

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