Robust estimates of a high
 N
 e
 /
 N
 ratio in a top marine predator, southern bluefin tuna

Waples, Robin S.; Grewe, Peter M.; Bravington, Mark W.; Hillary, Richard; Feutry, Pierre

doi:10.1126/sciadv.aar7759

Cited by 52 publications

(82 citation statements)

References 45 publications

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“…Estimates of Ne and the absence of evidence for a recent, anthropogenic decline support the notion that the South African population is relatively healthy, as previously indicated by mark-recapture and beach meshing catch data 34,36 . Estimates of Ne found here closely approximate the mean estimate of the number of adult sharks obtained by mark-recapture data (16,700) 36 . This is in agreement with previous findings of high Ne/Nc ratios in the East Australian C. taurus population 65,66 and other elasmobranchs, such as the zebra shark, Stegostoma fasciatum 17 and the sandbar shark, Carcharhinus plumbeus 18 .…”

Section: Discussionsupporting

confidence: 82%

“…Reported average Ne/Nc ratios across a range of species from different taxa range from approximately 0.1 to 0.5 [11][12][13] . Ne/Nc ratios in teleost fish with high fecundity, high juvenile mortality and sweepstake recruitment (type III survivorship), can be as low as 10 -5 14, 15 (but see Waples et al 16 ).…”

Section: Introductionmentioning

confidence: 99%

“…Effective population size Ne can be estimated from genetic and demographic data, or a combination thereof 16,21,22 . As it is usually difficult to collect enough data on demographic parameters in wild populations, genetic approaches have become widely popular, and are particularly useful when studying rare or elusive organisms, such as elasmobranchs 23 .…”

Section: Introductionmentioning

confidence: 99%

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A globally threatened shark, Carcharias taurus, shows no population decline in South Africa

Klein

Merwe

Dicken

et al. 2020

Preprint

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Knowledge about the demographic histories of natural populations helps to evaluate their conservation status, and potential impacts of natural and anthropogenic pressures. In particular, estimates of effective population size obtained through molecular data can provide useful information to guide management decisions for vulnerable populations. The spotted ragged-tooth shark Carcharias taurus (also known as the sandtiger or grey nurse shark) is widely distributed in warm-temperate and subtropical waters, but has suffered severe population declines across much of its range as a result of overexploitation. Here, we used multilocus genotype data to investigate the demographic history of the South African C. taurus population. Using approximate Bayesian computation and likelihood-based importance sampling, it was found that the population underwent a historical range expansion that may have been linked to climatic changes during the late Pleistocene. There was no evidence for a recent anthropogenic decline. Together with census data suggesting a stable population, these results support the idea that fishing pressure and other threats have so far not been detrimental to the local C. taurus 2 population. The results reported here indicate that South Africa could possibly harbour the last remaining, relatively pristine population of this widespread but vulnerable top predator.

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Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A globally threatened shark, Carcharias taurus, shows no population decline in South Africa

Klein

Merwe

Dicken

et al. 2020

Preprint

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“…This method is based on the identification of pairs of close relatives (parents–offspring or half sibling pairs). Pairs of related individuals sampled at different locations can also inform on migration (Feutry et al., ) and be used for estimating N e (Waples, Grewe, Bravington, Hillary, & Feutry, ). However, as these approaches have not been much used, further studies are needed to evaluate their merits and limits.…”

Section: Discussionmentioning

confidence: 99%

Estimating effective population size of large marine populations, is it feasible?

et al. 2018

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Sustainable exploitation of marine populations is a challenging task relying on information about their current and past abundance. Fisheries‐related data can be scarce and unreliable making them unsuitable for quantitative modelling. One fishery independent method that has attracted attention in this context consists in estimating the effective population size (Ne), a concept founded in population genetics. We reviewed recent empirical studies on Ne and carried out a simulation study to evaluate the feasibility of estimating Ne in large fish populations with the currently available methods. The detailed review of 26 studies found that published empirical Ne values were very similar despite differences in species and total population sizes (N). Genetic simulations for an age‐structured fish population were carried out for a range of population and samples sizes, and Ne was estimated using the Linkage Disequilibrium method. The results showed that already for medium‐sized populations (1 million individuals) and common sample sizes (50 individuals), negative estimates were likely to occur which for real applications is commonly interpreted as indicating very large (infinite) Ne. Moreover, on average, Ne estimates were negatively biased. The simulations further indicated that around 1% of the total number of individuals might have to be sampled to ensure sufficiently precise estimates of Ne. For large marine populations, this implies rather large samples (several thousands to millions of individuals). If however such large samples were to be collected, many more population parameters than only Ne could be estimated.

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“…The latter, which is assumed to follow a negative binomial distribution with mean λ and parameter φ, may be influenced by many unknown factors and is not usually directly available for estimating φ. Recently, Waples et al (2018) developed a method for obtaining a minimum bound for such a parameter from fecundity data and showed that the variance is almost Poisson-like in southern bluefin tuna. However, this method does not reflect ocean stochasticity, which may cause family-correlated survivorship of offspring after spawning.…”

Section: Discussionmentioning

confidence: 99%

Nearly unbiased estimator of adult population size based on within-cohort half-sibling pairs incorporating flexible reproductive variation

Akita¹

2018

Preprint

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Close-kin mark-recapture (CKMR) is a kinship-based method for estimating adult abundance. However, the application of CKMR is limited to using a kinship relationship that is not affected by family-correlated survivorship, which leads to a biased estimation. We developed a nearly unbiased estimator of the number of mothers in a population, which is based on the known maternal half-sibling relationship found within the same cohort. Our method allowed for variance of the averaged offspring number per mother (between-age variation) and for variance of the offspring number among mothers with the same reproductive potential (within-age variation). Estimators of its variance and coefficient variation were also provided. The performance of the estimators was quantitatively evaluated by running an individual-based model. Our results provide guidance for (i) a sample size to archive the required accuracy and precision when the order of mother size is available and (ii) a degree of uncertainty regarding the estimated mother size when information about the mother size is not available. Taken together, these findings offer an opportunity to shed light on the usefulness of analysing within-cohort half-sibling pairs and will greatly widen the scope of the CKMR method.

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Robust estimates of a high N _e / N ratio in a top marine predator, southern bluefin tuna

Abstract: Genetic and demographic analyses indicate good conservation news for southern bluefin tuna.

Cited by 52 publications

References 45 publications

A globally threatened shark, Carcharias taurus, shows no population decline in South Africa

A globally threatened shark, Carcharias taurus, shows no population decline in South Africa

Estimating effective population size of large marine populations, is it feasible?

Nearly unbiased estimator of adult population size based on within-cohort half-sibling pairs incorporating flexible reproductive variation

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Robust estimates of a high N e / N ratio in a top marine predator, southern bluefin tuna

Abstract: Genetic and demographic analyses indicate good conservation news for southern bluefin tuna.

Cited by 52 publications

References 45 publications

A globally threatened shark, Carcharias taurus, shows no population decline in South Africa

A globally threatened shark, Carcharias taurus, shows no population decline in South Africa

Estimating effective population size of large marine populations, is it feasible?

Nearly unbiased estimator of adult population size based on within-cohort half-sibling pairs incorporating flexible reproductive variation

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Robust estimates of a high N _e / N ratio in a top marine predator, southern bluefin tuna