Tracking the rising extinction risk of sharks and rays in the Northeast Atlantic Ocean and Mediterranean Sea

Rachel H L Walls,Nicholas K Dulvy

doi:10.1038/s41598-021-94632-4

Abstract

The loss of biodiversity is increasingly well understood on land, but trajectories of extinction risk remain largely unknown in the ocean. We present regional Red List Indices (RLIs) to track the extinction risk of 119 Northeast Atlantic and 72 Mediterranean shark and ray species primarily threatened by overfishing. We combine two IUCN workshop assessments from 2003/2005 and 2015 with a retrospective backcast assessment for 1980. We incorporate predicted categorisations for Data Deficient species from our previously published research. The percentage of threatened species rose from 1980 to 2015 from 29 to 41% (Northeast Atlantic) and 47 to 65% (Mediterranean Sea). There are as many threatened sharks and rays in Europe as there are threatened birds, but the threat level is nearly six times greater by percentage (41%, n = 56 of 136 vs. 7%, n = 56 of 792). The Northeast Atlantic RLI declined by 8% from 1980 to 2015, while the higher-risk Mediterranean RLI declined by 13%. Larger-bodied, shallow-distributed, slow-growing species and those with range boundaries within the region are more likely to have worsening status in the Northeast Atlantic. Conversely, long-established, severe threat levels obscure any potential relationships between species’ traits and the likelihood of worsening IUCN status in the Mediterranean Sea. These regional RLIs provide the first widespread evidence for increasing trends in regional shark and ray extinction risk and underscore that effective fisheries management is necessary to recover the ecosystem function of these predators.

Highlights

Overfishing is the most imminent threat to many marine organisms[1]
In 2003/2005 and in 2 01519–21; (3) the Northeast Atlantic and Mediterranean Sea may be a ‘canary-in-the-coal mine’ for collapse and recovery of fish populations because of the combination of a long history of exploitation[22], high scientific c apacity[17], substantial modern fishing e ffort[23], and divergent patterns of fisheries development and management[24]; and (4) extinction risk categorisations have already been predicted for the Data Deficient species in these regions in previous r esearch[25], presenting the opportunity to include these Data Deficient species in the Red List Indices (RLIs) as well
We provide a regional synthesis of the changing extinction risk for sharks and rays in the Northeast Atlantic and Mediterranean Sea

Summary

Introduction

Overfishing is the most imminent threat to many marine organisms[1]. Governments need repeated comprehensive assessments of extinction risk to effectively monitor the status of marine b iodiversity[2] and track progress towards global biodiversity and sustainable development t argets[3] if they are to halt declines, prevent more local extinctions, and recover species. The RLI includes species listed under six categories, in ascending order of threat: Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, and Extinct, but excludes the Data Deficient c ategory[4]. We focus on the sharks, rays, and ghost sharks (Class Chondrichthyes, ‘sharks and rays’) in the Northeast Atlantic Ocean and Mediterranean Sea for four reasons: (1) sharks and rays have the greatest percentage of ‘threatened’ species (i.e. Vulnerable, Endangered, or Critically Endangered) of any taxonomic Class of marine organisms[13], with numerous populations worldwide already locally or regionally extinct due to overfishing[1,14,15], including many from the Northeast Atlantic and Mediterranean Sea[16,17,18]; (2) the status of sharks and rays in this region has been comprehensively assessed twice: Scientific Reports | (2021) 11:15397. We build on the knowledge that sharks and rays with slower life histories (i.e. slower growth and population turnover rates27–29) and shallower depth distributions (i.e. higher exposure to fishing activity due to limited depth refuge30) are more likely to be categorised as threatened on the IUCN Red L ist[25,30] by exploring the likelihood of shark and ray Red List status worsening between assessment years based on these biological and ecological traits

Methods

Results

Conclusion