Site fidelity,survival and conservation options for the threatened flapper skate (Dipturus cf. intermedia)

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Taxonomic confusion and market mislabelling of threatened skates: important consequences for their conservation status

• 1. The iconic European common skate (Dipturus batis) has been described as the first clear case of a fish species brought to the brink of extinction by commercial fishing. Its listing was upgraded to Critically Endangered on the 2006 IUCN Red List of Threatened Species. According to FAO fishery statistics, France is responsible for 60.2% of the 502 tonnes reported as ‘D. batis’ in the 2005 world landings.
• 2. Noticeable phenotypic differences within the species and inconsistencies in published data on its sexual maturation required careful re‐examination of its taxonomy. Morphology, genetics, and life history reveal that two distinct species have been erroneously confused since the 1920s under the single scientific name D. batis. Here it is argued that they should be resurrected as two valid species. The common skate D. batis species‐complex is split into two nominal species, the blue skate (provisionally called D. cf. flossada) and the flapper skate (D. cf. intermedia) with maximum lengths of 143.2 cm and 228.8 cm respectively.
• 3. This taxonomic confusion puts into question all previously accumulated data based on D. batis. Its endangered status highlights the need for an extensive reassessment of population collapses with accurately identified species. In 2006/2007 an extensive survey (4110 skates, 14.081 tonnes by weight) was conducted in the main French ports of the D. batis species‐complex and relatives (D. oxyrinchus, D. nidarosiensis and Rostroraja alba) that are mixed together in landings under the names ‘D. batis’ and ‘D. oxyrinchus’.
• 4. The survey reveals that official fishery statistics mask species‐specific declines, due to the mislabelling of five species under only two landing names. Trends in landings since the 1960s and the life history of these species suggest a dramatic decline and collapse of the spawning stock, preventing the recovery of relict populations.
• 5. The risk of extinction of these depleted species may be higher than previously assessed and might be unavoidable without immediate and incisive conservation action. Copyright © 2009 John Wiley & Sons, Ltd.

     

Common dolphins in the Gulf of Corinth are Critically Endangered

1. Regional populations (“subpopulations”) of globally abundant species can be exposed to human impacts that threaten their viability. Given the value of cetacean subpopulations as evolutionary significant units, keystone and umbrella species, it is important to assess their conservation status separately and propose area-specific conservation measures.
2. We used a threat assessment process and applied IUCN Red List criteria to a regional population of common dolphins Delphinus delphis in the semi-enclosed Gulf of Corinth, Greece. We compiled subpopulation-specific information about abundance and trends, estimated the geographic range of the subpopulation (area of occupancy and extent of occurrence), and calculated the probability of extinction through stochastic modelling.
3. The subpopulation qualified as Endangered according to criteria A (population size reduction over three generations) and B (geographic range), and as Critically Endangered under criteria C (population size and decline) and D (very small or restricted population). The probability of extinction was estimated to be ≥50% in three generations, qualifying the subpopulation as Critically Endangered under criterion E (quantitative analysis). We concluded that the subpopulation should be classified as Critically Endangered.
4. Considering the high extinction risk faced by common dolphins in the Gulf of Corinth, we recommend that: (a) immediate action is taken to mitigate anthropogenic activities known or suspected to have a negative impact on cetaceans in the area (particularly commercial fishing); and (b) a marine protected area is established in the Gulf of Corinth as a management tool for enforcing conservation action and facilitating the recovery of common dolphins.

     

Diversity and origins of giant guitarfish and wedgefish products in Singapore

1. Giant guitarfishes (Glaucostegidae) and wedgefishes (Rhinidae) are some of the most threatened marine taxa in the world, with 15 of the 16 known species exhibiting global population declines and categorized as Critically Endangered according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The recent inclusion of all species in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) necessitates more rigorous enforcement by regulatory authorities.
2. Challenges in regulating the trade of giant guitarfish and wedgefish products due to difficulties in visual identification of processed products and labelling issues impede enforcement. The aim of this study is to characterize the diversity and origins of associated traded products that were commercially available in Singapore, one of the world's top importers and re-exporters of shark and ray products.
3. A total of 176 samples of elasmobranch products were obtained between June and December 2019 from fishery ports and various retailers in Singapore. By applying cytochrome c oxidase subunit I gene barcoding, 31 elasmobranch species were detected, with 55% of the species considered threatened (Critically Endangered, Endangered, or Vulnerable) based on the IUCN Red List and 35% of species listed in CITES Appendix II. Four species of giant guitarfishes and wedgefishes were commercially available to consumers in fresh forms of whole fish, fillet, and fin, as well as dried and cooked meats.
4. DNA barcoding has proven to be an effective tool for identifying elasmobranch products that are impossible to recognize visually and would aid enforcement of CITES trade regulations. This work underscores the urgent need to step up enforcement of marine wildlife regulations and draw public attention to the elasmobranch trade.

     

Multiple survey methods reveal greater abundance of endangered pupfish in restored habitats

1. Freshwater organisms inhabiting arid ecosystems are imperilled by human alterations to water-limited landscapes. This is especially true among desert-dwelling cyprinodontid fishes, 90% of which are imperilled by habitat destruction within limited or shrinking ranges. Constructing habitats that mimic natural habitat form and function may provide a tool for species conservation, especially within freshwater protected areas. However, pupfish population assessments within degraded compared with restored habitats are infrequent, and few comparisons among survey methods exist.
2. Density estimates were developed for Endangered Comanche Springs pupfish Cyprinodon elegans throughout altered and restored habitats in a freshwater protected area by using mark–recapture and N-mixture models fitted to data collected using minnow trap and visual count survey methods. This allowed comparison of habitats, survey methods, and statistical methods commonly used to generate population size estimates for imperilled pupfish.
3. Population estimates varied across major habitat types and were largest among habitats constructed to mimic naturally occurring ciénegas. Estimates using visual counts were higher than estimates from minnow traps where water was deeper and where macroalgae cover was highest. N-mixture models generally estimated higher abundances than mark–recapture and were not limited by recapture ability.
4. The results provide strong evidence that restored habitats house greater abundances of pupfish, but survey and statistical methods commonly used to detect these differences have trade-offs in performance according to the habitats surveyed. This work benefits the field of conservation biology by providing guidance for existing and emerging monitoring programmes assessing abundance-based fish responses to habitat improvements.

     

Long-term catch trends and risk assessment of the Critically Endangered white-spotted wedgefish (Rhynchobatus djiddensis) from South Africa

1. The white-spotted wedgefish (Rhynchobatus djiddensis) is a Critically Endangered shark-like ray in the family Rhinidae. Throughout its Western Indian Ocean distribution, it is targeted for its valuable meat and fins and is reported to have undergone major population declines. However, there remains a need for species specific time-series data to accurately assess localized population declines.
2. This study used two independent long-term (37 and 40 years) time-series catch data from competitive shore angling and shark nets to investigate the size composition and catch per unit effort (CPUE) and conduct a risk assessment for the population on the east coast of South Africa.
3. From 1977 to 2017 the competitive shore fishery captured 7,703 individual R. djiddensis, whilst shark nets in the same region captured 2,856 individuals from 1981 to 2017. Individuals captured in the nets had a sex ratio of 1.8:1 females to males, and were larger than those caught by the anglers. Although the mean annual sizes of net-caught individuals were above the size of reported sexual maturity, there was little evidence to suggest that any individuals captured were reproductively active.
4. Both the competitive shore fishery and shark net catches exhibited strong seasonal trends with the majority of R. djiddensis catches occurring from October to May peaking in austral summer. Standardized CPUE from the competitive shore fishery declined substantially between 1977 and 2017 and shark net catches exhibited a significant (p < 0.05) fourfold decline in annual nominal CPUE from 1981 to 2017.
5. Ultimately, a risk assessment showed a 65.1% decline in abundance over a period of three generation lengths, which indicates that the sampled population of R. djiddensis in South Africa should be classified as Endangered according to the IUCN Red List using criterion A2b. The conservation implications of this are discussed.

     

Elasmobranch fishing and trade in Sarawak,Malaysia, with implications for management

1. Many shark and ray (elasmobranch) species are threatened with extinction, due to overfishing and commercial trade
2. Sarawak is situated in Malaysian Borneo in the Coral Triangle: a global priority region for elasmobranch conservation. Malaysia is the world’s eighth largest elasmobranch fishing nation, and Sarawak is one of Malaysia’s largest fishing states, yet there are limited species-specific data on catch and trade of elasmobranchs to support conservation and fisheries management decisions.
3. This study presents landing site and market survey data, collected in Sarawak from January 2017 to December 2019. Geographical, temporal and operational trends in volumes of catch and trade are explored; the total volume, value and species composition of Sarawak's local elasmobranch markets is estimated; and simple size-based indicators are used to assess the sustainability of elasmobranch utilization for several conservation-priority and frequently traded species, including Critically Endangered and CITES-listed scalloped hammerhead sharks (Sphyrna lewini) and bottlenose wedgefish (Rhynchobatus australiae).
4. The results conservatively estimate that >26,500 elasmobranchs (~90,000 kg) are locally traded in Sarawak annually, worth ~US$125,000 per year at the market level.
5. Trade is dominated by small to medium-sized coastal requiem sharks (Carcharhinidae) and stingrays (Dasyatidae), with endangered and CITES-listed species making up 26% and 32% of total landings and trade, respectively.
6. High proportions of immature individuals were recorded, with evidence of overfishing for several species, based on simple size-based indicators.
7. Several options are outlined for improving management of elasmobranch fishing and trade in the future, including spatio-temporal closures and live release protocols, which could help to reduce the mortality of critically endangered species and implement CITES. Such measures could have large conservation impacts with limited socio-economic cost, since these species make up <5% of the total value of the elasmobranch market. However, management plans need to be co-designed with full participation of affected coastal communities in order to be ethical and effective.

     

Assessing the conservation status of mangroves in Rakhine,Myanmar

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Data-mining social media platforms highlights conservation action for the Mediterranean Critically Endangered blue shark Prionace glauca

1. The Mediterranean Sea represents an area of elevated risk of extinction for sharks, where data deficiency is a pervasive problem.
2. To compensate for such a paucity of information, this study investigated the use of social media content as a complementary approach to evaluate the distribution and habitat use of the Critically Endangered blue shark Prionace glauca in coastal waters, as well as public perceptions of the sharks.
3. Through social media data mining a total of 146 records, comprising 158 individual blue sharks approaching Italian coastal waters, have been recorded from 2011 to 2020.
4. This study revealed that, over the past decade, blue sharks regularly visited Italian coastal habitats for extended periods of time. Differences in the temporal distribution of blue sharks by sex and size appear to be linked to reproductive activity. The higher number of adult females approaching the shore in spring and the increase in young-of-the-year (YOY) sightings in the following months possibly indicate parturition in coastal waters. Spatial analyses also showed that certain Italian coastal areas, such as those in Calabria and Puglia, were preferred coastal habitats for this species.
5. Results also indicate that social media platforms can be considered an ever-growing source of data on wildlife, which can shed light on the occurrence and distribution of endangered shark species in poorly known habitats. Furthermore, social media platforms should be used for awareness campaigns to educate the public, as this study showed that negative reactions to shark encounters remain widespread.

     

Conservation status assessment and a new method for establishing conservation priorities for freshwater mussels (Bivalvia: Unionida) in the middle and lower reaches of the Yangtze River drainage

1. The freshwater mussel (Unionida) fauna of the Yangtze River is among the most diverse on Earth. In recent decades, human activities have caused habitat degradation in the river, and previous studies estimated that up to 80% of the mussel species in the Yangtze River are Threatened or Near Threatened with extinction. However, a comprehensive and systematic evaluation of the conservation status of this fauna has yet to be completed.
2. This study evaluated the conservation status of the 69 recognized freshwater mussel species in the middle and lower reaches of the Yangtze River, using the criteria published by the International Union for Conservation of Nature (IUCN). A new method for prioritizing species for conservation was then developed and applied termed Quantitative Assessment of Species for Conservation Prioritization (QASCP), which prioritizes species according to quantifiable data on their distribution and population status, life history, and recovery importance and potential.
3. IUCN assessments showed that 35 (51%) species in the study region are Threatened or Near Threatened (11 Endangered, 20 Vulnerable, 4 Near Threatened). In addition, 16 species (23%) could not be assessed owing to data deficiency. Key threats to the freshwater mussel biodiversity of the Yangtze River include pollution, habitat loss and fragmentation, loss of access to host fish, and overharvesting of mussels and their host fish. The genera Aculamprotula, Gibbosula, Lamprotula, Pseudodon, Ptychorhynchus, and Solenaia were identified as particularly threatened.
4. Data availability allowed QASCP assessment of 44 species. Only Solenaia carinata, regionally Endangered under IUCN criteria, achieved the highest QASCP rank, i.e. First Priority. The five species assessed as Second Priority were considered either regionally Endangered (one), Vulnerable (three), or Data Deficient (one) under IUCN criteria. The 23 Third Priority species were assessed as regionally Endangered (two), Vulnerable (15), Near Threatened (two), or Least Concern (four).

     

Substantial advancement in aquaria rearing methods to assist recovery of an Endangered soft coral

1. The temperate soft coral Dendronephthya australis has been listed as Endangered in NSW, Australia, owing to its restricted geographic range, rapidly declining populations, and a number of escalating threats. Research to assess practical methods for aquarium cultivation of D. australis for rehabilitation of wild populations is considered a high priority.
2. Previous attempts at restoration by transplanting D. australis fragments have had limited success, but identified key challenges, which included achieving attachment to substrates and identifying appropriate foods to maximize survival.
3. This study presents the results of experiments promoting the attachment of cuttings (nubbins) removed from donor colonies to moveable substrates (small concrete discs). Using a balanced orthogonal experimental design, three feeding regimes were tested: live artemia, live rotifers and dry powdered zooplankton.
4. Donor colony survival and growth were also monitored over a 6 month period in the field.
5. An overall nubbin survival rate of 100% was achieved under all three feeding regimes. Attachment rates were similar across feeding treatments, although nubbin behavioural responses (percentage of open polyps before feeding) suggested some preference for live rotifers.
6. The cutting removal process had no significant effect on donor colonies in the wild, indicating that this is a sustainable approach for restoration.
7. Overall, this study substantially advances the methodology for maintaining an Endangered azooxanthellate soft coral in aquaria and provides valuable input for management programmes aimed at implementing transplantation into the wild to aid species recovery.

     

Occupancy dynamics of rare cyprinids after invasive fish eradication

1. The eradication of invasive species is a management strategy implemented to eliminate adverse impacts of invaders on native species communities. After eradications, follow‐up studies are done to confirm eradication of the invasive species and the short‐term recovery of the native species, but long‐term monitoring to confirm full population recovery and stability is often not completed.
2. In this study, long‐term monitoring of native fishes was carried out over 5 years after the eradication of an invasive fish from the Rondegat River, South Africa. Forty‐six sites distributed along four river sections were sampled for presence/absence using underwater cameras and snorkel surveys. Density data were collected by snorkel surveys.
3. Using multi‐season occupancy models, the annual probability of colonization and local extinction of the native fishes and annual rate of change in occupancy along the river were estimated. Changes in native fish densities across time and across the control and treatment sections were analysed using Kruskal–Wallis analysis, followed by Dunn's post‐hoc test.
4. Probability of colonization and local extinction differed for each native fish species and may have been affected by extrinsic factors, such as rainfall, and intrinsic density‐dependent factors, hypothesized from the density data. The occupancy rates of change revealed that the two Near Threatened fish species have reached an occupancy dynamic equilibrium but the Endangered fish has not, suggesting that other conservation efforts may be needed.
5. Long‐term monitoring of native fishes after an eradication programme has confirmed the successful removal of the invader and the recovery and stability of the community. However, successful eradication was not sufficient for full recovery of all species; additional conservation management strategies are needed to secure the population stability and persistence of endangered fishes. We recommend that eradication programmes, regardless of locality, should employ long‐term monitoring to ensure full recovery of a native fish community.

     

The thin edge of the wedge: Extremely high extinction risk in wedgefishes and giant guitarfishes

1. The process of understanding the rapid global decline of sawfishes (Pristidae) has revealed great concern for their relatives, the wedgefishes (Rhinidae) and giant guitarfishes (Glaucostegidae), not least because all three families are targeted for their high‐value and internationally traded ‘white’ fins.
2. The objective of this study was to assess the extinction risk of all 10 wedgefishes and six giant guitarfishes by applying the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria, and to summarize the latest understanding of their biogeography and habitat, life history, exploitation, use and trade, and population status. Three of the 10 wedgefish species had not been assessed previously for the IUCN Red List.
3. Wedgefishes and giant guitarfishes have overtaken sawfishes as the most imperilled marine fish families globally, with all but one of the 16 species facing an extremely high risk of extinction through a combination of traits: limited biological productivity; presence in shallow waters overlapping with some of the most intense and increasing coastal fisheries in the world; and overexploitation in target and by‐catch fisheries, driven by the need for animal protein and food security in coastal communities and the trade in meat and high‐value fins.
4. Two species with very restricted ranges, the clown wedgefish (Rhynchobatus cooki) of the Malay Archipelago and the false shark ray (Rhynchorhina mauritaniensis) of Mauritania, may be very close to extinction.
5. Only the eyebrow wedgefish (Rhynchobatus palpebratus) is not assessed as Critically Endangered, with it occurring primarily in Australia where fishing pressure is low and some management measures are in place. Australia represents a ‘lifeboat’ for the three wedgefish and one giant guitarfish species occurring there.
6. To conserve populations and permit recovery, a suite of measures will be required that will need to include species protection, spatial management, by‐catch mitigation, and harvest and international trade management, all of which will be dependent on effective enforcement.

     

Integrating local ecological knowledge,citizen science and long‐term historical data for endangered species conservation: Additional records of angel sharks (Chondrichthyes: Squatinidae) in the Mediterranean Sea

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Use of diet and body condition assessments as intermediate indicators of translocation success in the Critically Endangered Philippine crocodile (Crocodylus mindorensis)

1. Intermediate metrics of translocation success are useful for long-lived, slow to mature species where survival and reproduction happen over decades.
2. With fewer than 150 individuals in the wild, the Critically Endangered Philippine crocodile (Crocodylus mindorensis) is one of the most threatened species on Earth. This study presents the first analysis of diet and body condition of wild Philippine crocodiles and headstarted (i.e. captive-reared) individuals released into the wild over the last decade, and uses these results to show how diet and body condition can be pertinent intermediate metrics of translocation success.
3. Analyses of stomach contents revealed 17 different aquatic and terrestrial invertebrate and vertebrate prey species. Interestingly, 70% of Philippine crocodiles showed snails to be the predominent prey type, followed by fish (36.7%), birds (33.3%) and reptiles (33.3%). More than 50% of crocodiles consumed the invasive golden apple snail, a leading agricultural pest. Regardless of crocodile history (wild vs. headstarted) or size class (juvenile vs. adult), no evidence was found for dietary differences in percentage occurrence, percentage composition or prey diversity.
4. Body condition was significantly higher in wild compared with headstarted individuals when analysed together in a pooled group, although neither group differed significantly from the standardized expectation, and headstarted individuals were not significantly different when body condition was derived independently for the two groups.
5. This study provides a working example of how assessing the convergence of diet and body condition between translocated and wild individuals can provide complementary monitoring parameters to demonstrate post-release establishment of translocated crocodylians. The congruent dietary composition and comparable body condition observed in this study suggest that headstarted crocodiles adapt well following release.
6. Crocodylus mindorensis survives in an agricultural landscape and is likely to play an ecologically important role by exploiting invasive species, reinforcing the importance of this species to local communities.

     

Recovery,conservation status,and environmental effects on arapaima populations in Guyana

1. Using population estimates that were made regularly between 2001 and 2013, the state of recovery of arapaima populations and their IUCN conservation status were assessed after they were almost extirpated from the upper Essequibo basin, Guyana. Recovery rates were compared across multiple areas with different degrees of access by fishers to evaluate effectiveness of conservation efforts.
2. Population estimates were also used to investigate the influence of environmental factors on arapaima abundance in lakes with different morphometries, vegetation, and water types and to determine the relationship between the numbers of spawning individuals and subsequent recruits (at about age 2 years).
3. The most recent census conducted in November–December of 2013 indicated a 5.6-fold increase in overall abundance compared with 2001, with 4,591 individuals, of which 1,932 were juveniles (1.0–1.5 m total length) and 2,659 adults.
4. Assessment of conservation status following IUCN criteria indicated that arapaima populations in the upper Essequibo basin in 2001 would have been considered borderline Critically Endangered, but in 2013 after conservation interventions, status would be categorized as Near Threatened.
5. Arapaima in the Essequibo basin appear to favour larger but shallow lakes with low conductivity, clear water, and abundant aquatic macrophytes. Stock–recruitment relationships suggest that the entire upper Essequibo basin population may still be growing and that there is approximately a 1:1 juvenile to adult ratio. This ratio of juveniles to adults across all areas suggests a paucity of young fishes to sustain overall population growth, which might reflect widespread illegal removals of young fishes in the basin.
6. Comparisons of arapaima densities in the upper Essequibo basin with those at four localities across the Amazon Basin, suggest that with enhanced conservation efforts in the Essequibo, populations could potentially increase two-fold or more.

     

Life history traits and conservation actions for the Maugean skate (Zearaja maugeana), an endangered species occupying an anthropogenically impacted estuary

1. The Maugean skate, Zearaja maugeana, is endemic to two isolated western Tasmanian (Australia) estuaries. The species' persistence in one of these estuaries (Bathurst Harbour) is uncertain, while the other estuary (Macquarie Harbour), potentially the remaining stronghold for the species, is an anthropogenically impacted system.
2. Key life-history parameters were studied to inform conservation actions for this species. Reproductive information was obtained using non-lethal methodologies, circulating concentrations of sex steroids and ultrasonography. Growth and age parameters were estimated based on vertebral sections from a small sample of individuals.
3. Females and males reached 870 and 760 mm total length, respectively. The species reached a maximum age of at least 10 years. Females and males attained 50% sexual maturity at 665 and 633 mm total length, respectively, probably maturing somewhere between four and six years of age. Females displayed an asynchronous, discontinuous reproductive cycle, being able to reproduce throughout the year, with a probable decline in reproductive activity during summer. No egg cases were observed in-utero. Males produce sperm all year round, with a peak in testosterone production during spring–autumn.
4. Conservation strategies for Z. maugeana will need to focus on reducing anthropogenic impacts on the environmental health, the primary impacts being altered river flows associated with the production of hydroelectricity and increased nutrient load associated with salmonid aquaculture. There is a need to better understand how reproductive success, egg survival and recruitment are affected by these environmental challenges if the future well-being of this species is to be secured.

     

From scientific obscurity to conservation priority: Research on angler catch rates is the catalyst for saving the hump‐backed mahseer Tor remadevii from extinction

1. The mahseer (Tor spp.) fishes of South and Southeast Asia are iconic megafaunal species that are highly valued by recreational anglers. Knowledge on their populations is limited owing to the challenges associated with sampling these large‐bodied fishes (>50 kg) in remote monsoonal rivers.
2. Despite its global iconic status among recreational anglers, the hump‐backed mahseer of the Cauvery River (South India) lacked a valid scientific name and was on a trajectory towards extinction until its rapidly declining population status was established by analyses of angler catch records.
3. Angling records from 1998 to 2012 showed that mahseer catch rates had increased in this period. The resulting publication in Aquatic Conservation (AQC) highlighted the positive role of catch‐and‐release angling in providing information on data‐poor species. However, further analyses showed that these catches comprised not one but two distinct phenotypes.
4. Before 1993, all mahseer captured were hump‐backed; since then, a blue‐fin phenotype appeared in catches and subsequently dominated them. These results triggered further studies indicating that the hump‐backed mahseer was the endemic Tor remadevii and that the blue‐fin was the invasive Tor khudree, introduced in 1976 and then stocked periodically from hatcheries.
5. The initial AQC publication successfully demonstrated the high value of organized angling as a monitoring tool for data‐poor fishes and its application to assessing the temporal population patterns of large‐bodied fishes in monsoonal rivers. It was also the catalyst for initiating subsequent studies on T. remadevii that, together, enabled its recent assessment as ‘Critically Endangered’ on the International Union for Conservation of Nature (IUCN) Red List. In the absence of the AQC paper, and the subsequent studies that it triggered, it is highly probable that the species would have remained on a trajectory towards rapid extinction. Instead, the first major steps to safeguarding its future have been taken.

     

Population structure,distribution and habitat use of the Critically Endangered Angelshark,Squatina squatina,in the Canary Islands

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Recovery potential of smalltooth sawfish,Pristis pectinata,in the United States determined using population viability models

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