Half a century of global decline in oceanic sharks and rays

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Discussion Overview

The discussion revolves around the decline of oceanic sharks and rays, primarily attributed to overfishing, and draws parallels to declines in other species such as insects and birds. It explores the implications of these declines for biodiversity and the potential for a mass extinction event.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant presents data indicating a 71% decline in global abundance of oceanic sharks and rays since 1970, linked to increased fishing pressure.
  • Another participant draws a comparison between the decline of sharks and rays and the decline of insect populations.
  • Several participants mention the decline of bird species, referencing historical extinctions such as the passenger pigeon and current lists of rare birds.
  • A participant cites a book discussing the impact of deforestation on bird populations, suggesting awareness of biodiversity issues has existed for some time.
  • Some participants reference scientific arguments suggesting that the planet may be experiencing a sixth mass extinction event, supported by various articles.

Areas of Agreement / Disagreement

Participants express concern over the decline of various species, but there is no consensus on the implications or the extent of the crisis. Multiple competing views remain regarding the causes and significance of these declines.

Contextual Notes

Limitations include the difficulty in measuring declines and extinction risks for specific species, as well as the reliance on various datasets and indicators that may have different assumptions and methodologies.

Who May Find This Useful

This discussion may be of interest to ecologists, conservationists, and those studying biodiversity loss and its implications for ecosystems.

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TL;DR
We find that, since 1970, the global abundance of oceanic sharks and rays has declined by 71% owing to an 18-fold increase in relative fishing pressure.
Overfishing is the primary cause of marine defaunation, yet declines in and increasing extinction risks of individual species are difficult to measure, particularly for the largest predators found in the high seas1–3. Here we calculate two well-established indicators to track progress towards Aichi Biodiversity Targets and Sustainable Development Goals4,5: the Living Planet Index (a measure of changes in abundance aggregated from 57 abundance time-series datasets for 18 oceanic shark and ray species) and the Red List Index (a measure of change in extinction risk calculated for all 31 oceanic species of sharks and rays). We find that, since 1970, the global abundance of oceanic sharks and rays has declined by 71% owing to an 18-fold increase in relative fishing pressure.

https://www.nature.com/articles/s41586-020-03173-9
 
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Biology news on Phys.org
Similar to the decline in insects we have been hearing about for several years.
 
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jim mcnamara said:
Birds as well. Some like passenger pigeons are extinct. Audubon has a list of once more common species, species that have become rare. Here is one list:

http://focusonnature.com/BirdListRareBirdsNorthAmerica.htm
Any in there that are warm, cuddly and cute?

Besides the sharks and scary insects, that is.:wink:
 
John Terborgh 'Where have all the birds gone' 1989 -- discusses the impact of deforestation of Cuba and the steep decline of North American songbirds that used to overwinter there.
https://www.amazon.com/dp/0691024286/?tag=pfamazon01-20

It is not like we have been unaware of an impending problem.
 
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