Increasing rate of species discovery in sharks coincides with sharp population declines: implications for biodiversity

Randhawa, Haseeb S.; Poulin, Robert; Krkošek, Martin

doi:10.1111/ecog.00793

Cited by 23 publications

(14 citation statements)

References 87 publications

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“…We examined a total of 91 shark species in this study, which is less than one-fifth of all described shark species known to date (Randhawa et al 2015). However, a more complete analysis of the influence of diet on tapeworm richness would require host diet and tapeworm records to become available for many more shark species which are currently data deficient.…”

Section: Discussionmentioning

confidence: 99%

Host diet influences parasite diversity: a case study looking at tapeworm diversity among sharks

Rasmussen¹,

Randhawa²

2018

Mar. Ecol. Prog. Ser.

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In theory, animal diets may act as important filters for different parasite species. However, there is currently a lack of empirical research looking at host diet as a potential predictor of parasite diversity among different host species. The aim of this study was to assess the influence of several host diet features (including diet breadth, diet composition, and trophic level) on tapeworm diversity in sharks, relative to other key factors, including host size, habitat, phylogeny, latitude, and depth. Data on these host features were compiled from a comprehensive analysis of literature records including 91 different shark species, and 3 measures of tapeworm diversity were examined: tapeworm species richness, tapeworm taxonomic distinctness (TD), and variance in tapeworm TD. The diet breadth of a shark species was revealed to be a better predictor of tapeworm species richness than other host features examined to date. Host size, trophic level, diet TD, latitudinal range, and the mid-point of a shark's depth range also significantly influenced tapeworm richness when analyses were ad justed to prevent confounding by phylogenetic re lation ships between hosts. The TD of tapeworm assemblages was influenced by diet breadth, diet TD, host size, and depth range when analysed independently of host phylogeny. Overall, our findings demonstrate that aspects of host diet have important consequences for parasite diversity in sharks. We em phasise that studies of parasite diversity in other systems should more seriously consider including aspects of host diet (particularly diet breadth) as potential key predictors of parasite diversity.

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Section: Discussionmentioning

confidence: 99%

Host diet influences parasite diversity: a case study looking at tapeworm diversity among sharks

Rasmussen¹,

Randhawa²

2018

Mar. Ecol. Prog. Ser.

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“…In rainforests, canopy living and plant-feeding beetles were better described than ground living species (Stork et al, 2008). Sharks at higher trophic levels have been described earlier although this will be correlated with larger body size (Randhawa et al, 2014). More host-specific parasitic helminths of freshwater fish in Canada and fleas (Krasnov et al, 2005) have also been described later.…”

Section: Other Factorsmentioning

confidence: 92%

Factors influencing when species are first named and estimating global species richness

Costello

Lane

Wilson

et al. 2015

Global Ecology and Conservation

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a b s t r a c tEstimates of global species richness should consider what factors influence the rate of species discovery at global scales. However, past studies only considered regional scales and/or samples representing <0.4% of all named species. Here, we analysed trends in the rate of description for all fish species (2% of all named species). We found that the number of species described has slowed for (a) brackish compared to marine and freshwater species, (b) large compared to small sized fish, (c) geographically widespread compared to localised, (d) species occurring in the tropics and northern hemisphere compared to southern hemisphere, and (e) neritic (coastal) species compared to pelagic (offshore) species. Most (68%) of the variation in year of description was related to geographic location and depth, and contrary to expectations, body size was a minor factor at just 6% (on a standardised scale). Thus most undiscovered species will have small geographic ranges, but will not necessarily be of smaller body size than currently known species. Accordingly, global assessments of how many species may exist on Earth need to account for geographic variation.

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“…However, there are numerous reasons why the trait distribution and exposure to threatening processes might be different. For example, most recently discovered sharks have been found in the deep sea (Randhawa et al, 2015) and are relatively small-bodied, beyond the reach of most fisheries, hence those Data Deficient deepwater species may actually be Least Concern because they have refuge from the main threatening process of overfishing. Conversely, many recently resolved species complexes, such as devil rays, eagle rays, and skates may be highly exposed to fisheries and hence the newly described ‘Data Deficient’ species might already be highly threatened (Iglésias et al, 2010; White & Last, 2012).…”

Section: Introductionmentioning

confidence: 99%

Predicting the conservation status of Europe’s Data Deficient sharks and rays

Dulvy

2019

Preprint

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Shark and ray biodiversity is threatened primarily by overfishing and the globalisation of trade, and Europe has been one of the most documented heavily fished regions for a relatively long time. Yet, we have little idea of the conservation status of the hundreds of Data Deficient shark and ray species. It is important to derive some insight into the status of these species, both to understand global extinction rates and also to ensure that any threatened Data Deficient species are not overlooked in conservation planning. Here, we developed a biological and ecological trait model to predict the categorical conservation status of 26 Northeast Atlantic and 15 Mediterranean Sea Data Deficient sharks and rays. We first developed an explanatory model based on all species evaluated on the International Union for Conservation of Nature (IUCN) Red List of Threatened SpeciesTM, using maximum body size, median depth (as a proxy for fisheries exposure), and reproductive mode, and then predicted the status of all Data Deficient species. Almost half of Northeast Atlantic (46%, n=12 of 26), and two-thirds of Mediterranean (67%, n=10 of 15) Data Deficient species are predicted to be in one of the three IUCN threatened categories. Northeast Atlantic Data Deficient species are predicted to be 1.2 times more threatened than evaluated species (38%, n=36 of 94), whereas threat levels in the Mediterranean Sea are relative for each (66%, n=38 of 58). This case study is intended for extrapolation to the global shark and ray dataset upon completion of the global IUCN Red List assessment. Trait-based, categorical prediction of conservation status is a cost-effective approach towards incorporating Data Deficient species into (i) estimates of lineage-wide extinction rates, (ii) revised protected species lists, and (iii) Red List Indices, thus preventing poorly known species from reaching extinction unnoticed.

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Increasing rate of species discovery in sharks coincides with sharp population declines: implications for biodiversity

Cited by 23 publications

References 87 publications

Host diet influences parasite diversity: a case study looking at tapeworm diversity among sharks

Host diet influences parasite diversity: a case study looking at tapeworm diversity among sharks

Factors influencing when species are first named and estimating global species richness

Predicting the conservation status of Europe’s Data Deficient sharks and rays

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