Red‐list status and extinction risk of the world's whales, dolphins, and porpoises

Abstract

To understand the scope and scale of the loss of biodiversity, tools are required that can be applied in a standardized manner to all species globally, spanning realms from land to the open ocean. We used data from the International Union for the Conservation of Nature Red List to provide a synthesis of the conservation status and extinction risk of cetaceans. One in 4 cetacean species (26% of 92 species) was threatened with extinction (i.e., critically endangered, endangered, or vulnerable) and 11% were near threatened. Ten percent of cetacean species were data deficient, and we predicted that 2–3 of these species may also be threatened. The proportion of threatened cetaceans has increased: 15% in 1991, 19% in 2008, and 26% in 2021. The assessed conservation status of 20% of species has worsened from 2008 to 2021, and only 3 moved into categories of lesser threat. Cetacean species with small geographic ranges were more likely to be listed as threatened than those with large ranges, and those that occur in freshwater (100% of species) and coastal (60% of species) habitats were under the greatest threat. Analysis of odontocete species distributions revealed a global hotspot of threatened small cetaceans in Southeast Asia, in an area encompassing the Coral Triangle and extending through nearshore waters of the Bay of Bengal, northern Australia, and Papua New Guinea and into the coastal waters of China. Improved management of fisheries to limit overfishing and reduce bycatch is urgently needed to avoid extinctions or further declines, especially in coastal areas of Asia, Africa, and South America.

Management and research efforts are failing dolphins, porpoises, and other toothed whales

“…There are several ecotypes of Orcinus orca and it may in fact represent a species complex 29 , here we assess it as a single species but this assessment should be revisited if multiple species are formally recognized in future. The mean predicted IUCN Red List Index for all Data Deficient species was greater than 0.7, indicating that these species are most likely Near Threatened or Least Concern, and suggesting that recent estimates which speculated that one or two of these species are likely to be threatened may be overstated 28 .

Figure 4 Predicted IUCN Red List index for Data Deficient Species.

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“…To assess and contextualise the threatened status of marine small cetaceans, we used data from the IUCN Red List 16 , 28 . Using an estimate based on the current distribution of IUCN Red List assessments ( n = 77) as much as one-quarter (25.0%) of small cetaceans may be threatened with extinction (Critically Endangered, Endangered, or Vulnerable).…”

“…Small cetaceans are less threatened than other marine vertebrate groups which display similar life-history characteristics, such as the great whales (46.7%), pinnipeds (33.3%), and chondrichthyans (37.3%), but are more threatened than marine bony fish (3.73%). At present only 20 species have had their population trends assessed, 19 of which are believed to have decreasing populations, no species have yet been assessed to have stable populations, and only 1 species has been assessed as having an increasing population 16 , 28 . Further, the proportion of species threatened with extinction and IUCN Red List Index 16 (the mean across species groups when Extinct species are assigned a value of 0.0, Critically Endangered a value of 0.2, Endangered 0.4, Vulnerable 0.6, Near Threatened 0.8, and Least Concern 1.0) of small cetaceans has remained roughly stable for nearly 30 years.…”

“…Fluctuations in the Red List Index are mainly in response to the discovery of new species or the re-assessment of previously Data Deficient species following new guidelines on the assignment of Red List Status to previously Data Deficient species (Fig. 1 ), which mask an overall decline in small cetacean Red List Status 28 . Taken together, this suggests that small cetaceans are likely to be experiencing a continued but gradual decline worldwide.…”

Environmental DNA reveals fine scale spatial and temporal variation of prey species for marine mammals in a Scottish marine protected area

“…Over a quarter of all European marine mammal species are threatened as a result of overfishing, shipping traffic, pollution, changes in prey dynamics and habitat degradation (Avila et al, 2018; Braulik et al, 2023), jeopardising the important ecosystem functions marine mammals provide (Estes et al, 2016). Marine protected areas (MPAs) are the main tool used to protect marine mammals from human impacts.…”