Even As Populations Of Other Large Fish Improve, The Threat Of Extinction For Sharks Grows
Successful fisheries management and conservation efforts have helped bring some species of tuna and billfish back from decades of population reductions. This includes southern bluefin tuna, black marlins, and swordfish. New evidence reveals that populations of other large fish improve, the threat of extinction for sharks grows.
Author:Rhyley CarneyReviewer:Paula M. GrahamNov 15, 202222.5K Shares327.2K Views
Successful fisheries management and conservation efforts have helped bring some species of tuna and billfish back from decades of population reductions. This includes southern bluefin tuna, black marlins, and swordfish. New evidence reveals that even when populations of other large fish improve, the threat of extinction for sharks grows.
Accidental catches of sharks like oceanic whitetips and porbeagles are common in fisheries for tuna and billfish. And researchers explain in the November 11 issue of Science that a lack of devoted management of these species has meant that their risks of extinction continue to climb.
The study assesses the potential for extinction over the next roughly seven decades for 18 species of big ocean fish. Marine scientist Colin Simpfendorfer from Australia's James Cook University, who was not involved in this study, says it gives us a new perspective on the wide sea.
“„Most of this information was available for individual species, but the synthesis for all of the species provides a much broader picture of what is happening in this important ecosystem.- Colin Simpfendorfer, James Cook University in Australia
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Extinction Risk For Sharks
According to Maria José Juan-Jordá, a fisheries ecologist at the Spanish Institute of Oceanography in Madrid, large global biodiversity surveys in recent years have found decreases in species and habitats around the world. But our knowledge of these occurrences in the water is limited.
To address this informational gap, Juan-Jordá and her team consulted the Red List, a database maintained by the International Union for Conservation of Nature that ranks the threat of extinction facing various species. Species are ranked according to how close they are to extinction on the Red List Index. The group focused on tunas, billfish, and sharks because of the outsized roles they play in the open ocean's food web.
The Red List Index is reevaluated every four to ten years. Based on the Red List criteria, the new study created a method for monitoring extinction risk constantly across time, rather than simply at the IUCN intervals.
To do this, Juan-Jordá and her coworkers compiled data from fish stock assessments on the average age at reproductive maturity, changes in population biomass, and abundance for seven species of tuna, including the endangered southern bluefin and vulnerable bigeye, as well as six species of billfish, including the black marlin and sailfish, and five species of sharks. From 1950 to 2019, the researchers pooled their data to determine the extinction risk trends for 18 different species.
The researchers discovered that the danger of extinction for tunas and billfishes rose steadily in the second half of the 20th century, before beginning to decline for tunas in the 1990s and for billfishes in the 2010s. We know that the concurrent decline in fishing-related fatalities for these species is a direct cause of these changes.
Simpfendorfer thinks the findings are encouraging for billfish and tuna. However, the researchers found that three out of seven species of tuna and three out of six species of billfish are still classified as near threatened, vulnerable, or endangered.
Simpfendorfer warns that "now is not the time for complacency in controlling these species." However, several shark species are in trouble because they are taken accidentally when fishing for tuna and billfish.
Final Words
As for what can be done moving ahead, setting catch restrictions for certain species and developing sustainability objectives within tuna and billfish fisheries that go beyond only the targeted species to address the problem of sharks that are inadvertently taken.
Rhyley Carney
Author
Paula M. Graham
Reviewer
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