New species of hammerhead sharks
This month, five new species of hammerhead sharks were described by a team of scientists led by Dr. George H. Burgess, director of the Florida Program for Shark Research at the Florida Museum of Natural History at the University of Florida, and Dr. Marta Di Campo, a shark expert and associate professor of biological sciences at New Jersey Institute of Technology. The species were discovered in deep waters of the Atlantic Ocean.
“With the recent description of new species of hammerhead sharks, we now know that they are distributed widely and have a variety of body shapes and sizes,” Burgess said. “These five new species, however, show that they have extreme diversity in the types of denticles, the tiny, tooth-like structures, on their jaws.”
In the paper, “Revised family tree of the hammerhead sharks,” the researchers propose that these sharks may belong to the group of Chondrichthyes, or cartilaginous fish, and that they are closely related to some sharks that are found in the Indian and Pacific Oceans. They are also classified in the genus Orectolobus, one of the largest genera of cartilaginous fish.
Burgess, who has been studying hammerheads for nearly 30 years, has discovered seven new species of hammerhead sharks and named two new genera.
“These five new species are named in honor of individuals who have made important contributions to shark research,” said Burgess.
“The family Orectolobidae has a complicated history of classification and taxonomic changes,” said study co-author Caroline M. Arbour, a professor of biology at the University of Toronto. “It is wonderful that our new species and genera are now able to contribute to a better understanding of this family and their diversity.”
Place of hammerhead sharks in the taxonomy
“We hope this paper helps to move the hammerhead sharks from the category of ‘dwarf’ sharks, to a more common family of sharks,” said Burgess.
He added that it is important to recognize that this genus is extremely diverse and has not been well studied.
“This new genus and species represent a surprising discovery of a group of fishes with a great deal of diversity,” said Arbour. “With over 250 species in nine genera, the family Orectolobidae is among the largest families of sharks.”
“Sharks, like other fish, have complex migratory behavior, and this study provides new insights into their behavior,” said Dr. David Gruber, the Program Director of NSF’s Biological Sciences Directorate. “These findings may help us understand the origins of the migratory patterns of other fish and other animals.”
Conservation of hammerhead sharks
“Our findings have implications for conservation,” said Dr. Martin Smith, a marine biologist at NOAA’s Northeast Fisheries Science Center and the study’s lead author. “By studying sharks in their summer and winter habitats, we can understand how migratory patterns develop and how we can protect these areas.”
The researchers studied a shark species known as the sandbar shark, or Carcharhinus brami. Sandbar sharks are often found near the coast in the North Atlantic, particularly in coastal areas of New York and New Jersey.
The researchers analyzed the genomes of the sharks and used a variety of genetic and behavioral analyses to determine their movements. The scientists observed that, as they transitioned between their two seasonal locations, the sandbar sharks altered their body temperatures.
In addition, they noticed that as the sharks moved between these two seasonal regions, they moved to colder waters and entered into diel (day-night) patterns. Diel patterns are typical of species that are specialized for low-light or no-light environments.
The researchers believe these changes in behavior may be an adaptation to their habitat, where environmental conditions are changing rapidly.
“While the dusky shark has been given the all clear to remain in the Mid-Atlantic Shark Area, this study shows that there is still a high risk of an accidental catch of the smooth hammerhead sharks by fishermen,” said Ted Pietsch, Director of NOAA Fisheries Southeast Fisheries Science Center. “The population continues to show signs of recovery, and these protections will help ensure that these iconic animals remain protected for years to come.”
To assess the movements of the sharks, researchers tagged 12 sharks from a collection of 50 in mid-Atlantic waters in 2012 and 2013. Each tag allowed researchers to track the shark’s location and speed for 24 hours, a long enough period to determine the sharks’ general movement patterns. This data is combined with the sharks’ migratory behaviors and movement patterns to estimate their movements in the region.
Since 2012, the study’s authors have tagged 20 more sharks. Researchers also continue to track four sharks that were tagged in 2013 and have since died. The long-term tagging and tracking data has helped scientists determine the movements of sharks and their migratory patterns, providing a detailed picture of the species’ habits.
The researchers have been working with federal agencies, fishing industry groups and state governments to implement regulations that reduce the risks of incidental catch of these sharks. They also collaborate with researchers to develop improved methods for identifying these sharks, which has helped improve the scientific understanding of the shark’s movements.