Application of extinction risk and conservation criteria for assessing fish species in the lower La Plata River basin,South America

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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.

     

You can swim but you can't hide: the global status and conservation of oceanic pelagic sharks and rays

• 1. Fishing spans all oceans and the impact on ocean predators such as sharks and rays is largely unknown. A lack of data and complicated jurisdictional issues present particular challenges for assessing and conserving high seas biodiversity. It is clear, however, that pelagic sharks and rays of the open ocean are subject to high and often unrestricted levels of mortality from bycatch and targeted fisheries for their meat and valuable fins.
• 2. These species exhibit a wide range of life‐history characteristics, but many have relatively low productivity and consequently relatively high intrinsic vulnerability to over‐exploitation. The IUCN — World Conservation Union Red List criteria were used to assess the global status of 21 oceanic pelagic shark and ray species.
• 3. Three‐quarters (16) of these species are classified as Threatened or Near Threatened. Eleven species are globally threatened with higher risk of extinction: the giant devilray is Endangered, ten sharks are Vulnerable and a further five species are Near Threatened. Threat status depends on the interaction between the demographic resilience of the species and intensity of fisheries exploitation.
• 4. 4. Most threatened species, like the shortfin mako shark, have low population increase rates and suffer high fishing mortality throughout their range. Species with a lower risk of extinction have either fast, resilient life histories (e.g. pelagic stingray) or are species with slow, less resilient life histories but subject to fisheries management (e.g. salmon shark).
• 5. 5. Recommendations, including implementing and enforcing finning bans and catch limits, are made to guide effective conservation and management of these sharks and rays.

Copyright © 2008 John Wiley & Sons, Ltd.     

A 40-year chronology of the vulnerability of spinetail devil ray (Mobula mobular) to eastern Pacific tuna fisheries and options for future conservation and management

1. Tuna fisheries are among the largest and most valuable fisheries in the world, but most interact with many non-target species, including several of high conservation importance. The spinetail devil ray (Mobula mobular) – listed as ‘Endangered’ on the IUCN Red List of Threatened Species – is a commonly discarded bycatch species, particularly in the eastern Pacific Ocean, yet insufficient data exist to undertake a traditional population assessment.
2. A new ecological risk assessment approach designed for data-limited settings – Ecological Assessment of the Sustainable Impacts of Fisheries (EASI-Fish) – was used to reconstruct the historical vulnerability status of M. mobular and to simulate potential changes in its status under 45 hypothetical conservation and management measures. These involved various temporal closures of the eastern Pacific Ocean tuna fishery, decreasing post-capture mortality by improved handling and release practices, and combinations of the two.
3. The species was classified as ‘Least Vulnerable’ between 1979 and 1993, but became ‘Most Vulnerable’ from 1994, which coincided with a rapid spatial expansion of the industrial purse-seine fishery, and especially from 2011 following the rapid increase in the number of sets made on floating objects. Simulating the conservation and management measures in place in 2018 revealed that 31 of the 45 scenarios resulted in a change in classification of the species to ‘Least Vulnerable’, which primarily involved a reduction of post-capture mortality by as little as 20%.
4. It is fortuitous in that education of fishers to implement appropriate best handling and release practices is simpler, more rapid and more cost-effective than the implementation of fishery closures or gear modifications, which can be expensive and complex to implement and monitor and will probably result in substantial reduction in the catches of target species.

     

Status of the freshwater mussel (Unionidae) communities of the mainstem of the Leon River,Texas

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The impact of catastrophic channel change on freshwater mussels in the Hunter River system,Australia: a conservation assessment

• 1. Australia has a distinct suite of endemic freshwater mussel species, several of which are restricted to south‐eastern Australia, an intensively modified region supporting much of the nation's population and where pressures on freshwater ecosystems are increasing.
• 2. Surveys were made of 78 sites in the Hunter River system to determine the distribution and abundance of the six mussel species occurring in the region, to identify threatening processes and to locate populations of high conservation value.
• 3. Mussel populations were mainly distributed in the hydrologically stable southern Barrington rivers, where those in the Williams River have the highest conservation value. Strongholds for Hyridella drapeta were found in Wollombi Brook.
• 4. Mussels were not detected at 40% of the sites, some of which supported mussels in the past. These were mainly reaches that have undergone river metamorphosis.
• 5. Where found, most mussel populations had low densities and were highly fragmented. Major threats to these remnant populations are degradation of riparian and instream condition from agricultural activities, extreme climatic events (flood and drought) and the introduced macrophyte, Salvinia molesta.
• 6. While threat mitigation can be achieved by habitat protection and strategies to reconnect mussel populations, managers are largely unaware of this invertebrate group. Formal recognition of regionally threatened mussel populations would do much to focus efforts on conservation.
• 7. The proposed construction of a large dam on the Williams River is a potential threat to the most important mussel populations in the Hunter River system. Copyright © 2009 John Wiley & Sons, Ltd.

     

The extinction risk of New Zealand chondrichthyans

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A new genus and two new,rare freshwater mussel (Bivalvia: Unionidae) species endemic to Borneo are threatened by ongoing habitat destruction

1. Most of the Bornean endemic freshwater mussel (Unionida) species known to date have not been recorded by science for the past 50 years or more, owing to a lack of research effort and presumed population losses.
2. This study assessed current patterns and recent changes in the diversity and distribution of freshwater mussels in north-eastern Borneo. Physical surveys and interviews were conducted at 24 sites, and anecdotal evidence for current or historical presence of mussels was collected for a further 13 sites.
3. Native species, i.e. Schepmania sp. and Khairuloconcha sahanae gen. & sp. nov., were only found in one small stream of the Kinabatangan River basin within the Gomantong Forest Reserve, whereas the non-native Sinanodonta cf. woodiana was common across the study area.
4. Molecular phylogenetics (five genes) of the native taxa, including comparative material from West Kalimantan and Sarawak, revealed: (i) the presence of a new genus with two new, rare species: Khairuloconcha lunbawangorum sp. nov. in the Limbang River basin and K. sahanae in the Kinabatangan River basin; (ii) that Khairuloconcha and Ctenodesma form the Bornean endemic tribe Ctenodesmini trib. nov.; and (iii) that Schepmania represents another Bornean endemic tribe Schepmaniini trib. nov.
5. Both Khairuloconcha gen. nov. species are known from a single stream each and are apparently restricted to forest stream habitats where they occur at very low densities. Schepmania appears to have a severely contracted range in the Kinabatangan and adjacent basins. We urgently call for full protection of the currently known sites of K. lunbawangorum and K. sahanae, and development of an action plan to save the Bornean freshwater mussel fauna.

     

The native South American crayfishes (Crustacea,Parastacidae): state of knowledge and conservation status

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Changes in the distributions of freshwater mussels (Unionoida: Hyriidae) in coastal south‐eastern Australia and implications for their conservation status

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Freshwater mussels in Mediterranean-climate regions: Species richness,conservation status,threats, and Conservation Actions Needed

1. The five global Mediterranean-climate regions are experiencing alarming rates of freshwater biodiversity loss. Although freshwater mussels are recognized as important functional components in aquatic ecosystems, and are among the most threatened faunal groups globally, there has been no synthesis of the plight of this group within these regions.
2. Data from the International Union for Conservation of Nature (IUCN) Red List were reviewed to compare the conservation status, threats, and conservation actions needed for freshwater mussel species occurring in Mediterranean-climate regions (med-mussels) with those of other freshwater mussel species globally. The first comprehensive catalogue of med-mussel species was compiled using existing taxonomic literature.
3. There are 41 med-mussel species, 30 of which occur in the Mediterranean basin. Many regions have just a single species, and regions where multiple species occur generally only have between one and four species per river basin. Med-mussel species are almost twice as likely to be ‘Imperilled’, are affected by 2.4 times more threats, and require 3.5 times more conservation actions than non-med mussels. In many cases, the exact threats have not been identified.
4. In combination with low species richness, this level of imperilment means that Mediterranean-climate regions are at risk of losing the benefits that mussels provide to broader ecosystem functioning. The conservation of med-mussels can be improved by increasing our knowledge of species distributions, including the identification of cryptic species and significant management units, through population genetic work. In addition, recognizing the potential of ‘novel’ habitats and refuge areas could augment the management of this important functional group.

     

Gone with the wind: Seasonal distribution and habitat use by the reef manta ray (Mobula alfredi) in the Maldives,implications for conservation

1. Reef manta rays (Mobula alfredi) are one of the ocean's largest and most charismatic species. Pressure from targeted and bycatch fisheries coupled with their conservative life‐history traits including slow growth, late maturity, and low fecundity has led to catastrophic declines of the global population. The species is now listed as Vulnerable to Extinction on IUCN Red List of Threatened Species.
2. The global M. alfredi population is widely distributed in highly fragmented subpopulations. The Maldives supports the world's largest known subpopulation that undergoes seasonal migrations which are thought to be linked to peaks in ocean productivity induced by the South Asian Monsoon. Although the species is protected from targeted fisheries in the region, increasing pressures from habitat degradation and unsustainable tourism activities mean their effective conservation relies upon knowledge of the species' habitat use, seasonal distribution, and the environmental influences on such movements.
3. Photo‐ID sighting records collected between 2005 and 2017 were used to identify key aggregation sites throughout the archipelago, and multiple linear regression and prediction analysis identified the environmental variables affecting variations in the intra‐annual sighting frequency of M. alfredi.
4. Mobula alfredi were recorded at 273 different sites, 48 of which, with >100 sightings at each, were classified as key areas of habitat use. South‐west monsoon winds and chlorophyll‐a concentration predominantly affected the monthly percentage of M. alfredi sighted on the down‐current side of the atolls.
5. In a country where climate change and touristic pressure are increasingly threatening this species and its habitat, the identification of key areas of habitat use and temporal changes in the use of these sites highlight the areas that should be prioritized for protection enabling more effective conservation management.

     

Detecting the brook floater,a freshwater mussel species at risk,using environmental DNA

1. The use of environmental DNA (eDNA) is a promising approach for the detection of aquatic species, including species at risk. One freshwater mussel species of interest in Atlantic Canada, the brook floater (Alasmidonta varicosa), is listed as being of Special Concern under the Species at Risk Act in Canada and as Vulnerable on the International Union for Conservation of Nature Red List. Further scientific data regarding species distribution and critical habitat is needed for the protection and conservation of this species.
2. The aim of this study was to design, optimize, and apply a species-specific quantitative polymerase chain reaction assay for the detection of brook floater from eDNA samples, and to assess temporal variability in brook floater eDNA quantities.
3. Through an eDNA survey performed in New Brunswick rivers in 2017 and 2018, brook floater DNA was found at a total of 16 out of 56 sites sampled. The amount of brook floater DNA detected at all 16 sites was always below the theoretical limit of detection of the assay, and, as such, results were classified as either ‘inconclusive’ or ‘suspected’.
4. The co-detection of eastern pearlshell (Margaritifera margaritifera), a more abundant freshwater mussel species in Atlantic Canada, was successfully used as a natural positive control.
5. Temporal variability in the amount of eDNA found in the water was also assessed at a site with a known brook floater population and minimal variability in eDNA quantities was observed from May to September.
6. These results provide researchers and managers with a new tool for the detection of the brook floater in support of conservation and monitoring efforts.

     

Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

1. River fish diversity is threatened by anthropogenic environmental alteration to landscapes. The early life-history stages of fish play an important role in maintaining diversity and population recruitment and can be heavily influenced by landscape patterns. Information on temporal and spatial distribution patterns of fish eggs and larvae is also important for biodiversity conservation and management of fish resources.
2. The Yangtze River possesses a high diversity of fishes, including many commercially important species. The economy along the lower reach of the river is well developed, and most of the area is experiencing high pressure from human impacts. This section of the Yangtze River connects with the largest freshwater lake in China at the upstream end and flows into the estuary at the downstream end. These two landscape features are likely to have a significant impact upon the spatial distributions of fish egg and larval assemblages.
3. Environmental variables, fish eggs, and larval assemblages were sampled in three locations, at Hukou, Anqing, and Jingjiang, in the lower reach of the Yangtze River. The results suggest that the higher number of species and greater abundance in upstream sites reflect the critical function of connectivity of Poyang Lake with the river for fish recruitment in the lower Yangtze. The delayed bloom of larval fish, occurrence of estuarine species, and a lower species number and abundance of freshwater fish downstream reflect the influence of tidal intrusion from the estuary.
4. This study highlights the value of maintaining natural river–lakes connectivity in the Yangtze River as a conservation measure. The connected river–lake system should be designated as a priority area for fish resource protection in the lower reach of the Yangtze River. We recommend further measures to break down barriers between the river and other lakes and to restore the natural lateral connectivity of the floodplain ecosystem.

     

Averting co-extinction: Successful mussel translocation rescues an endangered population of the European bitterling,Rhodeus amarus

1. Local extinctions break species interactions and have cascading effects throughout ecosystems; parasites are often severely affected. The European bitterling, Rhodeus amarus, is a cyprinid fish that parasitizes unionid mussels by laying eggs into the mussel gill cavity, where embryos develop and emerge as active juveniles; this relationship is obligatory for the bitterling.
2. This article describes a field experiment aimed at averting the secondary extinction of the European bitterling after a complete die-off of a freshwater mussel community, as a result of habitat destruction.
3. Approximately 5,000 unionid mussels were reintroduced within the short time frame in which the remnant bitterling population was still present at the site. Mussel survival was high, and bitterling resumed reproduction, with vigorous courtship observed within 24 hours of mussel release. Recruitment was successful, as evidenced by increased occupancy, densities, and relative frequencies in the fish assemblage. The frequency of sub-adults and young-of-the-year changed from 0% before mussel reintroduction to 80% a year later, and 50% 2 years later, when young-of-the-year contributed to about half of the young fish. No bitterling were observed at two control sites where mussels were not reintroduced.
4. This study exemplifies how the timely restitution of affiliate species can avert co-extinction. It also shows how the conservation of the bitterling within its historical distribution range can serve mussel conservation, including species that although not legally protected, are important keystone species and ecosystem engineers, shaping the structure and function of a broad range of freshwater habitats.

     

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.

     

Microsatellite analysis of genetic diversity and genetic structure of the Chinese freshwater mussel Solenaia carinata (Bivalvia: Unionidae)

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Prediction of potential freshwater pearl mussel habitat aids in discovery of a large population of Margaritifera laevis in Iturup Island,Russia

1. Freshwater pearl mussels (family Margaritiferidae) are sensitive to human impact and environmental changes. Large declines in their abundance have prompted studies of distribution and estimations of population densities.
2. Iturup Island, a part of Kuril Islands, Russia, is considered to be within the distribution area of freshwater pearl mussels, but this information is based on only two specimens collected several decades ago. Detailed survey of the island is challenging as most of its territory is nearly impassable.
3. A preliminary analysis of island rivers was carried out prior to the surveys to discover potential freshwater pearl mussel habitats. Based on previous experience from European Russia, freshwater pearl mussel habitat was expected to occur in rivers flowing out of lowland lakes.
4. Live individuals of Margaritifera laevis were found during surveys in one river together with the unionid Beringiana beringiana, which were also found in two other rivers where the predicted habitat occurred. Based on prediction and surveys, the occurrence of freshwater pearl mussels in other rivers of Iturup Island is unlikely.
5. Pearl mussels were concentrated in a small section of the Zmeika River with a population of about 100,000 mussels. Present threats to the population include overharvest of host fish masou salmon (Oncorhynchus masou).
6. Surveys using similar methods can help to reveal unknown freshwater mussel populations on other Kuril Islands and on the mainland.

     

Trophic niche overlap between native freshwater mussels (Order: Unionida) and the invasive Corbicula fluminea

1. Freshwater mussels (Order Unionida) are highly threatened. Interspecific competition for food sources with invasive alien species is considered to be one of the factors responsible for their decline because successful invaders are expected to have wider trophic niches and more flexible feeding strategies than their native counterparts.
2. In this study, carbon (δ¹³C: ¹³C/¹²C) and nitrogen (δ¹⁵N: ¹⁵N/¹⁴N) stable isotopes were used to investigate the trophic niche overlap between the native freshwater mussel species, Anodonta anatina, Potomida littoralis, and Unio delphinus, and the invasive bivalve Corbicula fluminea living in sympatry in the Tua basin (south-west Europe).
3. The species presenting the widest trophic niches were C. fluminea and A. anatina, which indicate that they have broader diets than U. delphinus and P. littoralis. Nonetheless, all the species assimilated microphytobenthos, sediment organic matter, and detritus derived from vascular plants, although with interspecific variability in the assimilated proportions of each source. The trophic niche of the invasive species overlapped with the trophic niche of all the native species, with the extent varying between sites and according to the species.
4. From the three native species analysed, Potomida littoralis may be at a higher risk for competition for food with C. fluminea in the Tua basin, if food sources become limited, because this native mussel presented the narrowest trophic niche across sites and the highest probability of overlapping with the trophic niche of C. fluminea.
5. Given the global widespread distribution of C. fluminea, the implementation of management measures devoted to the control or even eradication of this invasive alien species should be a conservation priority given its potential for competition with highly threatened native freshwater mussels.