Blue sharks swimming off the Azores, an island chain in the North Atlantic Ocean.
Credit: F. Vandeperre
Young sharks have a nursery school of sorts, and it's in the central North Atlantic, new research finds.
Baby blue sharks (Prionace glauca) spend the first two years of their lives hanging out in this mid-ocean region before splitting up by sex, according to the research, which tracked the movements of 37 sharksfor up to two and a half years.
"For the first time, this study shows the utilization of a discrete, oceanic nursery in an oceanic shark and how movements change throughout their lives," Frederic Vandeperre, a shark researcher at the University of the Azores in Portugal, said in a statement. "It offers a unique insight in the ecological adaptations to their open ocean habitat and highlights the challenges for their management." [On the Brink: A Gallery of Wild Sharks (Photos)]
Sharks are notoriously long-distance travelers, and researchers have long known that they tend to segregate themselves by age and sex throughout their lives. But the patterns of shark migration are still largely mysterious.
To pull back the curtain on blue sharks, Vandeperre and his colleagues tagged 37 male and female sharks of varying ages in the Azores, an island chain in the North Atlantic off of Europe. The team conducted tagging expeditions in each season throughout the year and captured both juveniles and adults.
The radio tags reported back data for long periods of time — up to 952 days in one female shark. In that time period, the female shark swam an incredible 17,484.8 miles (28,139 kilometers).
In analyzing the tag data, the researchers found a pattern in young sharks' travels. In the first two years of life, juvenile sharks hung out in the central North Atlantic, in a region delineated by the Azores to the north, the Great Meteor Seamount to the south and the Mid-Atlantic Ridge to the west. The study wasn't designed to investigate why young sharks prefer this area, but researchers suspect that the vulnerable babies may find fewer predators out in the open ocean.
In adulthood, the co-ed nature of the shark nursery vanished, the researchers found. Maturing females migrated seasonally, but tended to move toward tropical latitudes. Males moved south in the autumn and then migrated westward in winter before heading back toward the Azores in the spring. From there, the males expanded their range southward as they matured.
The fact that sharks of both sexes returned to the central Azores throughout their lives suggests this region is a key spot, perhaps serving as pupping grounds, the researchers report today (Aug. 13) in the journal PLOS ONE. Commercial fishing is common in this region, suggesting the need for conservation and protection measures for sharks in the central North Atlantic, they wrote.