As sharks face intense fishing–with over a million killed each year for their prized fins and for meat–shark researchers sketched out the state of the ocean’s top predators and wondered about their future.
Julia Baum studies the great sharks: large top predators including hammerheads, tiger sharks, great whites, bull and dusky sharks, oceanic whitetips, blues, threshers, and mako. All of these species have declined more than 80% in just the last 20 years, and many species have been cut down by 90% or more. Many are already listed as vulnerable or endangered by the IUCN.
Baum is showing that sharks play an underappreciated role in holding together marine food webs: as large sharks have disappeared due to recent exploitation, the smaller sharks, skates, and rays the big guys eat have exploded in population, sometimes by tenfold. Baum found that these mid-level predators can then devastate their own prey species. For example, the cownose ray that became more common as sharks declined went on to cause the collapse of scallop populations off the coast of North Carolina.
Sal Jorgensen is yielding insight into the lives of great whites. Until recently, they were thought to be exclusively coastal, but now the TOPP predator tagging project has revealed that the sharks regularly migrate thousands of miles offshore from California to as far as Hawaii, and spend a lot of time hanging out in a mysterious spot in the open ocean that researchers are calling the “white shark cafe.” Follow the white sharks and learn more about their lives here.
Colin Simpfendorfer drew particular attention to the problems faced by deepwater sharks. More than half of all shark species live down deep. All sharks have long generation times and low reproductive rates, making them vulnerable to threats, and these characteristics are even more exaggerated among the deep species. Despite the fact that trawl fishing has reduced these populations by 80-90% in two decades, the fishing of deepwater sharks remains unregulated virtually everywhere but the EU. Knowing how important sharks are to maintaining ecosystems (as in Baum’s work), Simpfendorfer says there is a dire need to protect these deep-sea giants now, while there may still be time to allow for their recovery.
