DNA reveals hidden threats to global shark populations

FIU scientists have discovered two major problems after analyzing small shark fins from Hong Kong markets — small coastal species are much more common in the international fin trade than previously thought and there is a burgeoning market for juveniles of large species.

Between 2014 and 2021, researchers analyzed the DNA of approximately 4,000 small shark fins collected from the markets. They looked at whole shark fins as well as trimmings taken from large and small fins, resulting in the most comprehensive assessment of species diversity of one of the world’s largest shark fin markets. Their analysis revealed small coastal shark species are more common and threatened by international fin trade than previously documented, according to new research recently published in Science Advances.

This combined approach highlighted important management gaps for 19 small threatened species that are not currently regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This includes the Triakidae family, which comprise some of the most threatened and most common species in the small fin category, according to Diego Cardeñosa, FIU biologist and lead author in the study. He says international trade regulations must be applied sooner rather than later to protect this family due to their increased extinction risk and unsustainable trade levels.

  
The DNA analysis revealed something else — the small shark species are not the only ones showing up in the fin trade as small fins. A quarter of the small fins were actually from juveniles of large shark species, including critically endangered hammerheads as well as threatened silky sharks and blacktips. This finding indicates substantial exploitation of juveniles could be affecting fisheries’ sustainability.
 
For more than a decade, fin trade research has primarily focused on large fins, but by surveying small ones, Cardeñosa said the actual species composition in the markets is quite different than what the previous assessments represent.
 
“Customs personnel around the world should thoroughly inspect small fin consignments as they likely hold species that are already regulated by international policies and should be accompanied by the right certificates,” Cardeñosa said. “Otherwise, they are being illegally traded.”
 
Cardeñosa is calling for enhanced surveillance and further research to ensure effective conservation strategies under emerging trade regulations. The study is a collaboration between Florida International University, University of Miami, Mote Marine Laboratory and others.

"While most of the management attention has been focused on large, iconic shark species caught in industrial open ocean fisheries, this study highlights that we must also pay attention to small, less famous species that are mainly caught in small-scale coastal fisheries. They may be small in size, but the catch of these species is huge and it is pushing many of them toward extinction," said Demian Chapman, co-lead of the study, and manager of Mote’s Sharks & Rays Conservation Research Program.