scholarly journals Diagnosing the dangerous demography of manta rays using life history theory

2013 ◽  
Author(s):  
Nicholas K Dulvy ◽  
Sebastián A. Pardo ◽  
Colin A. Simpfendorfer ◽  
John K. Carlson
Keyword(s):  
Life History ◽  
Life History Theory ◽  
Extinction Risk ◽  
Somatic Growth ◽  
Intrinsic Rate ◽  
Population Increase ◽  
Population Declines ◽  
Demographic Information ◽  
Age At Maturity ◽  
Manta Ray

The directed harvest and global trade in the gill plates of mantas, and other mobulid rays, has led to increased fishing pressure and steep population declines in some locations. The slow life history, particularly of the manta rays, is cited as a key reason why such species have little capacity to withstand directed fisheries. Here, we place their life history and demography in the context of other sharks and rays. Despite the limited availability of data, we use life history theory and comparative analysis to develop plausible ranges of somatic growth rate, annual pup production and age at maturity to estimate risk of extinction (maximum intrinsic rate of population increase rmax) using a variant of the classic Euler-Lotka model. Manta ray rmax is most sensitive to the length of the reproductive cycle, and the median rmax of 0.11 year-1(CI: 0.089-0.137) is one of the lowest known of the 106 sharks and rays for which we have comparable demographic information. In common with other unprotected, unmanaged, high-value large-bodied species with low or very low productivity, manta rays are unlikely to sustain unmonitored, unregulated exploitation and may face increasing local and regional extinction risk.

scholarly journals Diagnosing the dangerous demography of manta rays using life history theory

2013 ◽  
Author(s):  
Nicholas K Dulvy ◽  
Sebastián A. Pardo ◽  
Colin A. Simpfendorfer ◽  
John K. Carlson
Keyword(s):  
Life History ◽  
Life History Theory ◽  
Extinction Risk ◽  
Somatic Growth ◽  
Intrinsic Rate ◽  
Population Increase ◽  
Population Declines ◽  
Demographic Information ◽  
Age At Maturity ◽  
Manta Ray

The directed harvest and global trade in the gill plates of mantas, and other mobulid rays, has led to increased fishing pressure and steep population declines in some locations. The slow life history, particularly of the manta rays, is cited as a key reason why such species have little capacity to withstand directed fisheries. Here, we place their life history and demography in the context of other sharks and rays. Despite the limited availability of data, we use life history theory and comparative analysis to develop plausible ranges of somatic growth rate, annual pup production and age at maturity to estimate risk of extinction (maximum intrinsic rate of population increase rmax) using a variant of the classic Euler-Lotka model. Manta ray rmax is most sensitive to the length of the reproductive cycle, and the median rmax of 0.11 year-1(CI: 0.089-0.137) is one of the lowest known of the 106 sharks and rays for which we have comparable demographic information. In common with other unprotected, unmanaged, high-value large-bodied species with low or very low productivity, manta rays are unlikely to sustain unmonitored, unregulated exploitation and may face increasing local and regional extinction risk.

scholarly journals Maximum intrinsic rate of population increase in sharks, rays, and chimaeras: the importance of survival to maturity

2016 ◽  
Vol 73 (8) ◽  
pp. 1159-1163 ◽  
Author(s):  
Sebastián A. Pardo ◽  
Holly K. Kindsvater ◽  
John D. Reynolds ◽  
Nicholas K. Dulvy
Keyword(s):  
Life Span ◽  
Reproductive Output ◽  
Extinction Risk ◽  
Intrinsic Rate ◽  
Population Increase ◽  
Age At Maturity ◽  
Average Life ◽  
Demographic Parameter ◽  
Average Life Span

The maximum intrinsic rate of population increase (rmax) is a commonly estimated demographic parameter used in assessments of extinction risk. In teleosts, rmax can be calculated using an estimate of spawners per spawner, but for chondrichthyans, most studies have used annual reproductive output (b) instead. This is problematic as it effectively assumes all juveniles survive to maturity. Here, we propose an updated rmax equation that uses a simple mortality estimator that also accounts for survival to maturity: the reciprocal of average life-span. For 94 chondrichthyans, we now estimate that rmax values are on average 10% lower than previously published. Our updated rmax estimates are lower than previously published for species that mature later relative to maximum age and those with high annual fecundity. The most extreme discrepancies in rmax values occur in species with low age at maturity and low annual reproductive output. Our results indicate that chondrichthyans that mature relatively later in life, and to a lesser extent those that are highly fecund, are less resilient to fishing than previously thought.

scholarly journals Maximum intrinsic rate of population increase in sharks, rays, and chimaeras: the importance of survival to maturity

2016 ◽  
Author(s):  
Sebastián A. Pardo ◽  
Holly K. Kindsvater ◽  
John D. Reynolds ◽  
Nicholas K. Dulvy
Keyword(s):  
Reproductive Output ◽  
Extinction Risk ◽  
Intrinsic Rate ◽  
Population Increase ◽  
Age At Maturity ◽  
Demographic Parameter ◽  
Average Lifespan

AbstractThe maximum intrinsic rate of population increase rmax is a commonly estimated demographic parameter used in assessments of extinction risk. In teleosts, rmax can be calculated using an estimate of spawners per spawner, but for chondrichthyans, most studies have used annual reproductive output b instead. This is problematic as it effectively assumes all juveniles survive to maturity. Here, we propose an updated rmax equation that uses a simple mortality estimator which also accounts for survival to maturity: the reciprocal of average lifespan. For 94 chondrichthyans, we now estimate that rmax values are on average 10% lower than previously published. Our updated rmax estimates are lower than previously published for species that mature later relative to maximum age and those with high annual fecundity. The most extreme discrepancies in rmax values occur in species with low age at maturity and low annual reproductive output. Our results indicate that chondrichthyans that mature relatively later in life, and to a lesser extent those that are highly fecund, are less resilient to fishing than previously thought.

scholarly journals Quantifying the known unknowns: estimating maximum intrinsic rate of population increase in the face of uncertainty

2018 ◽  
Vol 75 (3) ◽  
pp. 953-963 ◽  
Author(s):  
Sebastián A Pardo ◽  
Andrew B Cooper ◽  
John D Reynolds ◽  
Nicholas K Dulvy
Keyword(s):  
Life History ◽  
Reproductive Output ◽  
Intrinsic Rate ◽  
Biological Information ◽  
Population Increase ◽  
Parameter Estimates ◽  
Age At Maturity ◽  
Management Options ◽  
Frequency Distributions ◽  
Life History Parameters

Abstract Sensitivity to overfishing is often estimated using simple models that depend upon life history parameters, especially for species lacking detailed biological information. Yet, there has been little exploration of how uncertainty in life history parameters can influence demographic parameter estimates and therefore fisheries management options. We estimate the maximum intrinsic rate of population increase (rmax) for ten coastal carcharhiniform shark populations using an unstructured life history model that explicitly accounts for uncertainty in life history parameters. We evaluate how the two directly estimated parameters, age at maturity αmat and annual reproductive output b, most influenced rmax estimates. Uncertainty in age at maturity values was low, but resulted in moderate uncertainty in rmax estimates. The model was sensitive to uncertainty in annual reproductive output for the least fecund species with fewer than 5 female offspring per year, which is not unusual for large elasmobranchs, marine mammals, and seabirds. Managers and policy makers should be careful to restrict mortality on species with very low annual reproductive output <2 females per year. We recommend elasmobranch biologists to measure frequency distributions of litter sizes (rather than just a range) as well as improving estimates of natural mortality of data-poor elasmobranchs.

scholarly journals Body mass, temperature, and depth shape the maximum intrinsic rate of population increase in sharks and rays

2021 ◽  
Author(s):  
Sebastián A. Pardo ◽  
Nicholas K. Dulvy
Keyword(s):  
Body Mass ◽  
Deep Sea ◽  
Extinction Risk ◽  
Deep Ocean ◽  
Intrinsic Rate ◽  
Population Increase ◽  
Theoretic Approach ◽  
Mass Scaling ◽  
Mass Temperature ◽  
Recovery Potential

AbstractAn important challenge in ecology is to understand variation in species’ maximum intrinsic rate of population increase,rmax, not least becausermaxunderpins our understanding of the limits of fishing, recovery potential, and ultimately extinction risk. Across many vertebrates, terrestrial and aquatic, body mass and environmental temperature across important correlatesrmaxacross species. In sharks and rays, specifically,rmaxis known be lower in larger species, but also in deep-sea ones. We use an information-theoretic approach that accounts for phylogenetic relatedness to evaluate the relative importance of body mass, temperature and depth onrmax. We show that both temperature and depth have separate effects on shark and rayrmaxestimates, such that species living in deeper waters have lowerrmax. Furthermore, temperature also correlates with changes in the mass scaling coefficient, suggesting that as body size increases, decreases inrmaxare much steeper for species in warmer waters. These findings suggest that there (as-yet understood) depth-related processes that limit the maximum rate at which populations can grow in deep sea sharks and rays. While the deep ocean is associated with colder temperatures, other factors that are independent of temperature, such as food availability and physiological constraints, may influence the lowrmaxobserved in deep sea sharks and rays. Our study lays the foundation for predicting the intrinsic limit of fishing, recovery potential, and extinction risk species based on easily accessible environmental information such as temperature and depth, particularly for data-poor species.

scholarly journals Data gaps and opportunities for comparative and conservation biology

2019 ◽  
Vol 116 (19) ◽  
pp. 9658-9664 ◽  
Author(s):  
Dalia A. Conde ◽  
Johanna Staerk ◽  
Fernando Colchero ◽  
Rita da Silva ◽  
Jonas Schöley ◽  
...  
Keyword(s):  
Life Histories ◽  
Extinction Risk ◽  
Average Rate ◽  
Demographic Data ◽  
Population Increase ◽  
Past Century ◽  
Population Declines ◽  
Background Rate ◽  
Death Rates ◽  
Data Gaps

Biodiversity loss is a major challenge. Over the past century, the average rate of vertebrate extinction has been about 100-fold higher than the estimated background rate and population declines continue to increase globally. Birth and death rates determine the pace of population increase or decline, thus driving the expansion or extinction of a species. Design of species conservation policies hence depends on demographic data (e.g., for extinction risk assessments or estimation of harvesting quotas). However, an overview of the accessible data, even for better known taxa, is lacking. Here, we present the Demographic Species Knowledge Index, which classifies the available information for 32,144 (97%) of extant described mammals, birds, reptiles, and amphibians. We show that only 1.3% of the tetrapod species have comprehensive information on birth and death rates. We found no demographic measures, not even crude ones such as maximum life span or typical litter/clutch size, for 65% of threatened tetrapods. More field studies are needed; however, some progress can be made by digitalizing existing knowledge, by imputing data from related species with similar life histories, and by using information from captive populations. We show that data from zoos and aquariums in the Species360 network can significantly improve knowledge for an almost eightfold gain. Assessing the landscape of limited demographic knowledge is essential to prioritize ways to fill data gaps. Such information is urgently needed to implement management strategies to conserve at-risk taxa and to discover new unifying concepts and evolutionary relationships across thousands of tetrapod species.

scholarly journals Population productivity of wedgefishes, guitarfishes, and banjo rays: inferring the potential for recovery

2019 ◽  
Author(s):  
Brooke M. D’Alberto ◽  
John K. Carlson ◽  
Sebastián A. Pardo ◽  
Colin A. Simpfendorfer
Keyword(s):  
Life History ◽  
Life History Theory ◽  
Maximum Size ◽  
Population Increase ◽  
Population Recovery ◽  
High Demand ◽  
Over Exploitation

AbstractRecent evidence of widespread and rapid declines of wedgefishes, guitarfishes, and banjo ray populations (Order Rhinopristiformes), driven by a high demand for their fins in Asian markets and the quality of their flesh, raises concern about their risk of over-exploitation and extinction. Using life history theory and incorporating uncertainty into a modified Euler-Lotka model, maximum intrinsic rates of population increase (rmax) were estimated for nine species from the four families of rhinopristiforms. Estimates of medianrmaxvaried from −0.04 to 0.60 year−1among the nine species, but generally increased with increasing maximum size. In comparison to 115 other species of chondrichthyans for whichrmaxvalues were available, the families Rhinidae and Glaucostegidae are relatively productive, while most species from Rhinobatidae and Trygonorrhinidae had relatively lowrmaxvalues. If the demand for their high value products can be addressed, then population recovery for this species is likely possible but will vary depending on the species.

scholarly journals Sympathy for the devil: a conservation strategy for devil and manta rays

2016 ◽  
Author(s):  
Julia M Lawson ◽  
Rachel HL Walls ◽  
Sonja V Fordham ◽  
Mary P O'Malley ◽  
Michelle R Heupel ◽  
...  
Keyword(s):  
Best Practice ◽  
Intrinsic Rate ◽  
Conservation Strategy ◽  
Population Increase ◽  
Geographic Ranges ◽  
Planning Approach ◽  
Scientific Attention ◽  
The Impact ◽  
The Devil ◽  
Manta Ray

Background. Increased interest in luxury products and Traditional Chinese Medicine, associated with economic growth in China, has been linked to depletion of both terrestrial and marine wildlife. Among the most rapidly emerging concerns with respect to these markets is the relatively new demand for gill plates, or Peng Yu Sai (“Fish Gills”), from devil and manta rays (subfamily Mobulinae). The high value of gill plates drives international trade supplied by largely unmonitored and unregulated bycatch and target fisheries around the world. Devil and manta rays are especially sensitive to overexploitation because of their exceptionally low productivity (maximum intrinsic rate of population increase). Scientific research, conservation campaigns, as well as international and national protections that restrict fishing or trade have increased in recent years. Many key protections, however, apply only to manta rays. Methods. We review the state of the development of scientific knowledge and capacity for these species, and summarise the geographic ranges, fisheries and national and international protections for these species. We use a conservation planning approach to develop the Global Devil and Manta Ray Conservation Strategy, specifying a vision, goals, objectives, and actions to advance the conservation of both devil and manta rays. Results and Discussion. Generally, there is greater scientific attention and conservation focused on Manta compared to Devil Rays. We discuss how the successes in manta ray conservation can be expanded to benefit devil rays. We also examine solutions for the two leading threats to both devil and manta rays – bycatch and target fisheries. First, we examine how can the impact of bycatch fisheries can be reduced through international measures and best-practice handling techniques. Second, we examine the role that responsible trade and demand can play in reducing target fisheries for gill plates. Our paper suggests that given similarities in sensitivity and appearance, particularly of the dried gill plate product, conservation measures may need to be harmonised particularly for the larger species in this subfamily.

Life history of the common blacktip shark, Carcharhinus limbatus, from central eastern Australia and comparative demography of a cryptic shark complex

2019 ◽  
Vol 70 (6) ◽  
pp. 834 ◽  
Author(s):  
Alastair V. Harry ◽  
Paul A. Butcher ◽  
William G. Macbeth ◽  
Jess A. T. Morgan ◽  
Stephen M. Taylor ◽  
...  
Keyword(s):  
Life History ◽  
Intrinsic Rate ◽  
Population Increase ◽  
Carcharhinus Limbatus ◽  
Eastern Australia ◽  
Comparative Demography ◽  
History Of ◽  
Similar Appearance ◽  
The Common ◽  
Central Eastern

Common and Australian blacktip sharks (Carcharhinus limbatus and Carcharhinus tilstoni) occur sympatrically in Australia, where they are reported as a complex because of their morphological similarities. This study provides the first description of the life history of C. limbatus using samples from central eastern Australia, where C. tilstoni is rare. Females (68–267cm total length (TL); n=183) and males (65–255cm TL; n=292) both matured at 8.3 years and 200cm TL, which exceeds the maximum length of C. tilstoni. Vertebral ageing revealed that female and male C. limbatus lived to 22 and 24 years respectively, exceeding known longevity in C. tilstoni. The mean (±s.d.) intrinsic rate of population increase calculated using a Euler–Lotka demographic method was 0.11±0.02year–1 for C. limbatus, compared with 0.17±0.02 and 0.20±0.03year–1 for two C. tilstoni stocks. Despite their similar appearance, these species differed in both their biological productivity and susceptibility to fishing activities. Monitoring of relative abundance should be a priority given they are likely to have divergent responses to fishing.

scholarly journals Sympathy for the devil: a conservation strategy for devil and manta rays

2016 ◽  
Author(s):  
Julia M Lawson ◽  
Rachel HL Walls ◽  
Sonja V Fordham ◽  
Mary P O'Malley ◽  
Michelle R Heupel ◽  
...  
Keyword(s):  
Best Practice ◽  
Intrinsic Rate ◽  
Conservation Strategy ◽  
Population Increase ◽  
Geographic Ranges ◽  
Planning Approach ◽  
Scientific Attention ◽  
The Impact ◽  
The Devil ◽  
Manta Ray

Background. Increased interest in luxury products and Traditional Chinese Medicine, associated with economic growth in China, has been linked to depletion of both terrestrial and marine wildlife. Among the most rapidly emerging concerns with respect to these markets is the relatively new demand for gill plates, or Peng Yu Sai (“Fish Gills”), from devil and manta rays (subfamily Mobulinae). The high value of gill plates drives international trade supplied by largely unmonitored and unregulated bycatch and target fisheries around the world. Devil and manta rays are especially sensitive to overexploitation because of their exceptionally low productivity (maximum intrinsic rate of population increase). Scientific research, conservation campaigns, as well as international and national protections that restrict fishing or trade have increased in recent years. Many key protections, however, apply only to manta rays. Methods. We review the state of the development of scientific knowledge and capacity for these species, and summarise the geographic ranges, fisheries and national and international protections for these species. We use a conservation planning approach to develop the Global Devil and Manta Ray Conservation Strategy, specifying a vision, goals, objectives, and actions to advance the conservation of both devil and manta rays. Results and Discussion. Generally, there is greater scientific attention and conservation focused on Manta compared to Devil Rays. We discuss how the successes in manta ray conservation can be expanded to benefit devil rays. We also examine solutions for the two leading threats to both devil and manta rays – bycatch and target fisheries. First, we examine how can the impact of bycatch fisheries can be reduced through international measures and best-practice handling techniques. Second, we examine the role that responsible trade and demand can play in reducing target fisheries for gill plates. Our paper suggests that given similarities in sensitivity and appearance, particularly of the dried gill plate product, conservation measures may need to be harmonised particularly for the larger species in this subfamily.

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