Indian Ocean humpback dolphin in the Menai Bay off the south coast of Zanzibar,East Africa is Critically Endangered

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Modelling effects of invasive species and drought on crayfish extinction risk and population dynamics

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A closer look at the bycatch of medium-sized and large sharks in the northern Catalan coast (north-western Mediterranean Sea): Evidence of an ongoing decline?

1. Historically, the Mediterranean Sea supported a rich shark fauna. Presently, however, populations of most shark species have significantly declined, largely due to intense fishing pressure.
2. Interviews with crew members of bottom trawlers, drifting longliners and bottom longliners operating off the Costa Brava (Catalonia, NE Spain) were conducted between October 2016 and July 2017 in order to gather information on the current bycatch rate of several shark species.
3. Interviews covered 41.2% of the fleet and respondents were asked for the bycatch of selected shark species—Alopias vulpinus, Cetorhinus maximus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Mustelus spp., Prionace glauca, and Squalus acanthias—in two distinct time periods.
4. Bottom trawlers captured the highest diversity of species (eight) followed by bottom longliners (seven), and drifting longliners (three). Most respondents (89.7%) declared having captured at least one shark from 2006 to 2016 but only 56.4% declared having captured at least one shark from 2016 to 2017.
5. From 2016 to 2017, the whole fleet captured 89 specimens of H. griseus (95% confidence interval (CI) = 145, 34), 14 of G. galeus (95% CI = 30, 0), 3 of A. vulpinus (95% CI = 8, 0), 3 of I. oxyrinchus (95% CI = 8, 0), 3 of C. maximus (95% CI = 6, 0), and no Mustelus spp. The total bycatch of P. glauca and S. acanthias was uncertain due to extremely loose confidence intervals.
6. A significant decline was perceived by fishermen in the bycatch of C. maximus and S. acanthias, whereas the bycatch of H. griseus was considered to have remained stable.
7. This study suggests a dramatic reduction in the abundance of most of the medium-sized and large sharks of the Costa Brava and the likely disappearance of Mustelus spp. from the area. Only H. griseus, S. acanthias, and P. glauca are still being bycaught frequently.

     

Annual survival probabilities of juvenile loggerhead sea turtles indicate high anthropogenic impact on Mediterranean populations

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Fisheries induced shift in sea snake community assemblages along the Konkan coast,India

1. The impacts of fisheries on several charismatic marine fauna have been a subject of global concern. Sea snakes share the same habitats as many commercially important fish species and often end up as fisheries bycatch.
2. Previous studies of bycatch from India have been limited to individual reports of mortality, with little information on the regional community structure of sea snakes. This study was carried out along the Konkan coast, off the central west coast of India, between 2016 and 2018, to determine trends in the bycatch of sea snakes in coastal fisheries.
3. In this study, 922 sea snakes were encountered in 916.57 gillnet haul hours and 449.16 trawlers haul hours of fishing, comprising largely of two species: beaked sea snake (Hydrophis schistosus) and spine-bellied sea snake (Hydrophis curtus) (83.05 and 16.94% respectively) which was in stark contrast to a similar study conducted in 2002–03, which recorded a dominance of H. curtus (84%) followed by H. schistosus (14%) in the same region. Both studies, however, indicated higher mortality in H. curtus than in H. schistosus in trawl nets.
4. This study highlights the significant impact of non-selective fishing practices on regional assemblages of other marine organisms such as sea snakes from South Asia, which has been relatively understudied, and the potential consequences for local ecosystems.

     

Setting the net lower: A potential low-cost mitigation method to reduce cetacean bycatch in drift gillnet fisheries

1. Bycatch is the most significant threat to marine megafauna (sea turtles, marine mammals, elasmobranchs, seabirds) worldwide, and the leading cause of the decline of several cetacean species. The bycatch issue in the Indian Ocean is poorly understood, but high bycatch levels in gillnet fisheries have been documented for the past two decades, in both small-scale and semi-industrial fisheries. Unfortunately, methods to reduce bycatch are often unavailable, financially non-viable or socially unacceptable to fishermen.
2. Using a network of trained boat captains in the tuna drift gillnet fishery in the Arabian Sea, targeted catch and bycatch data were collected from 2013 to 2017 off the coast of Pakistan (northern Indian Ocean). Two fishing methods using multifilament gillnets were used: surface deployment and subsurface deployment (i.e. headline of net set below 2 m depth).
3. Predicted catch rates for targeted species did not differ significantly between the two fishing practices, although a drop in tuna (6.2%) and tuna-like (10.9%) species captures was recorded in subsurface sets. The probability of cetacean bycatch, however, was 78.5% lower in subsurface than in surface sets.
4. Cetacean bycatch in tuna drift gillnet fisheries has the potential to be significantly reduced at a relatively low cost for fishers. However, further research with an appropriate sampling design and a large sample size is required to confirm the efficacy of the proposed mitigation method. The acceptability and adoption of subsurface setting by fishers also needs to be further investigated. Despite some limitations, this preliminary study also highlights the importance of crew-based observer data as an alternative source of data when observers cannot be deployed on fishing vessels.

     

Bycatch mortality can cause extirpation in four freshwater turtle species

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Isoëtes sabatina (Isoëtaceae,Lycopodiopsida): Taxonomic distinctness and preliminary ecological insights

1. Isoëtes sabatina is the rarest aquatic quillwort in Europe. Although recently found (2013) in Lake Bracciano (central Italy), the species is just one step away from extinction with an estimated population not exceeding 400 individuals and a spatial range of a few hundred square metres.
2. Lake Bracciano is a deep, oligo-mesotrophic Mediterranean volcanic lake that has been subjected to human activities. From January to October 2017, the lake experienced a dramatic water level decrease (up to −1.50 m), which significantly affected the littoral zone and the habitat of I. sabatina.
3. To improve the chances of survival of I. sabatina, the first eco-taxonomic investigation on this species was carried out to describe its genetic distinctness, physical and chemical requirements and companion species.
4. The phylogenetic position of I. sabatina was investigated by applying standard DNA barcoding methods. Simultaneously, during summer 2019, the physical and chemical features of water and sediments of the I. sabatina population and five small Alpine lakes colonized by Isoëtes echinospora – a supposed close relative – were characterized. These data were then compared with the available data on the trophic requirements of the target obligate aquatic Isoëtes, together with Isoëtes lacustris and Isoëtes malinverniana.
5. The present survey confirmed the taxonomic and ecological distinctness of I. sabatina – providing the first evidence of genetic differentiation from I. echinospora. Isoëtes sabatina grows in waters with temperature, conductivity and total alkalinity up to 30°C, 561 μS cm⁻¹ and 3.45 meq L⁻¹, respectively.
6. The edaphic requirements of I. sabatina confirm its outstanding conservation value, and this study offers a basic understanding of how to prevent its extinction. Now, all possible actions must be taken immediately to save this species.

     

Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with potentially large consequences

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Common bottlenose dolphin (Tursiops truncatus) interaction with fish farms in the Gulf of Ambracia,western Greece

1. Marine aquaculture, and its fast-growing development, has the potential for wider environmental, ecosystem, and biodiversity impacts. This study assesses the impact of fish farming on a bottlenose dolphin (Tursiops truncatus) population within the Gulf of Ambracia (western Greece) between 2007 and 2018. Two different study areas were defined in order to investigate differences on occurrence, abundance, behaviour, and seasonal fluctuations between them: a ‘control area’, in the north-western side of the Gulf; and a ‘fish farm area’, in the south west, where the highest density of fish farm cages is found.
2. A total of 169 daily surveys were dedicated to the control area and 74 days were dedicated to the fish farm area, yielding 104 and 37 sightings, respectively. Both the probability of detecting dolphins (U = 6,763.000, P = 0.002) and the group sizes (U = 578.000, P < 0.001) were smaller around fish farms.
3. Seasonality analyses were restricted to 2007–2008, as this was the period with year-round effort. Results revealed that dolphins were more frequently seen around fish farms in the winter (Kruskal–Wallis test, P = 0.036).
4. From the 40 identified individuals that were re-sighted at least 10 times during the study period, 21 used the fish farm area less than expected according to sampling effort, and 10 of them were never observed in that area (binomial test, P < 0.05).
5. The results revealed an impact of fish farms on the distribution of bottlenose dolphins in the Gulf of Ambracia. This information should be taken into consideration when defining ecosystem-based management measures within the management plan, which is currently in preparation for this Natura 2000 site.

     

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

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Freshwater turtle bycatch research supports science‐based fisheries management

1. Although it is sometimes difficult for researchers to ensure that their work is used by resource managers to make informed decisions, an example where this knowledge–action gap has been breached is in research published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) – among other journals – that has assisted fisheries managers in identifying strategies for reducing freshwater turtle bycatch in commercial hoop net fisheries in Ontario, Canada.
2. Research published in AQC has provided evidence towards a simple and effective method for preventing turtle bycatch mortality in hoop nets, which could be adopted by the fishers. Other research published in AQC evaluated the effect of bycatch mortality on the probability of persistence of turtle populations with population viability analyses, and outlined the need to minimize bycatch mortality to prevent local extirpation. Nine other papers have been published on freshwater turtle bycatch in Ontario, furthering our knowledge on this issue including seasonality and temperature effects on catches, other net modifications, post‐release effects and assisted recovery, and the perspectives of fishers.
3. The research results were presented to local resource managers with further discussions involving industry and stakeholders to minimize turtle bycatch mortality. Over several years, researchers have provided information to resource managers; however, when an incident of high turtle mortality caught the public eye, the research was readily available and changes in regulations were quick to occur.
4. Reasonably good communication among researchers, resource managers, industry, stakeholders, and the broader public allowed the rapid implementation of regulations to mitigate freshwater turtle bycatch mortality and bridged the knowledge–action gap between researchers and resource managers.
5. Both articles published in AQC had practical conservation impacts and were influential in providing local resource managers with feasible solutions, and the impetus to change regulations. These impacts extended to other jurisdictions and their monitoring programmes, where methods to reduce turtle bycatch mortality were also implemented.

     

Characterization of seabird bycatch in eastern Canadian waters, 1998–2011, assessed from onboard fisheries observer data

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First evidence of bubble-net feeding and the formation of ‘super-groups’ by the east Australian population of humpback whales during their southward migration

1. The recovery of overexploited populations is likely to reveal behaviours that may have been present prior to harvest but are only now reappearing as the population size increases. The east Australian humpback whale (Megaptera novaeangliae) population (group V, stock E1) has recovered well from past exploitation and is now estimated to be close to the pre-whaling population size.
2. Humpback whales were thought to follow a ‘feast and famine’ model historically, feeding intensively in high-latitude feeding grounds and then fasting while migrating and in calving grounds; however, there is growing evidence that animals may feed outside of known foraging grounds.
3. This short article reports on the first photographically documented evidence of bubble-net feeding by humpback whales in Australian coastal waters (n = 10 groups observed) and provides the first evidence of a second site in the southern hemisphere for the formation of ‘super-groups’ (n = 6 super-groups at discrete locations).
4. The formation of super-groups may be linked to changes in the type or density of prey available, either along the migratory route or in the feeding grounds of the previous summer. It is also possible that the increased population size following recovery make large group sizes while feeding more common. These findings strongly support evidence that feeding behaviour is not restricted to high-latitude foraging grounds in the Southern Ocean, and that prey consumption prior to leaving the coastal waters of Australia may be a significant component of the migratory ecology of this population.
5. Understanding how environmental variation influences the extent to which humpback whales depend on foraging opportunities along their migratory route, and where feeding occurs, will help to predict how future changes in the ocean will influence whale populations. This will also allow for more effective management measures to reduce the impact of threats during this important period of energy consumption.

     

Assessing the effectiveness of conservation management decisions: likely effects of new protection measures for Hector's dolphin (Cephalorhynchus hectori)

• 1. Fisheries bycatch affects many species of marine mammals, seabirds, turtles and other marine animals.
• 2. New Zealand's endemic Hector's dolphins overlap with gillnet and trawl fisheries throughout their geographic range. The species is listed as Endangered by the IUCN. In addition, the North Island subspecies has been listed as Critically Endangered.
• 3. Estimates of catch rates in commercial gillnets from an observer programme (there are no quantitative estimates of bycatch by amateur gillnetters or in trawl fisheries) were used in a simple population viability analysis to predict the impact of this fishery under three scenarios: Option (A) status‐quo management, (B) new regulations announced by the Minister of Fisheries in 2008 and (C) total protection.
• 4. Uncertainty in estimates of population size and growth rate, number of dolphins caught and other model inputs are explicitly included in the analysis. Sensitivity analyses are carried out to examine the effect of variation in catch rate and the extent to which fishing effort is removed from protected areas but displaced to unprotected areas.
• 5. These methods are applicable to many other situations in which animals are removed from populations, whether deliberately (e.g. fishing) or not (e.g. bycatch).
• 6. The current Hector's dolphin population is clearly depleted, at an estimated 27% of the 1970 population. Population projections to 2050 under Options A and B predict that the total population is likely to continue declining. In the case of Option B this is driven mainly by continuing bycatch due to the much weaker protection measures on the South Island west coast.
• 7. Without fishing mortality (Option C) all populations are projected to increase, with the total population approximately doubling by 2050 and reaching half of its 1970 population size in just under 40 years. Copyright © 2009 John Wiley & Sons, Ltd.

     

Modelling effects of disturbance on population dynamics of generalized crayfish life history strategies

1. Crayfish play a crucial ecological role and are often considered a keystone species within freshwater ecosystems; however, North American crayfish species face disturbance and ecological threats including invasive species and intensified drought.
2. Demographic models can allow examination of population dynamics of a targeted species under a wide variety of disturbance scenarios. In this study, crayfish population dynamics were modelled and their responses to simulated biological invasions and drought were assessed.
3. As life history data on crayfish are relatively rare, models were used to explore the population viability of four generalized species with distinct life history strategies under 11 disturbance scenarios. RAMAS-Metapop was used to construct stage-based demographic metapopulation models parameterized using vital rates from established literature sources.
4. Models indicated that populations respond differentially to disturbance based on life history. However, both r- and K-selected species appear to be highly susceptible to decline when faced with the additive effects of reduced carrying capacity resulting from invasion and reduced survival rates caused by drought.
5. Constructing models that explore a broad array of life histories and disturbance regimes can provide managers with tools to develop generalized, widely applicable conservation strategies in data-depauperate systems.

     

Southern right whale (Eubalaena australis), seasonal abundance and distribution at Head of Bight,South Australia

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Contextualizing the relative importance of habitat connectivity for metapopulation persistence: A case study of a critically endangered fish

1. Local population characteristics and habitat connectivity both have important influences on metapopulation persistence; however, the relative importance of each can vary depending on the ecological context, making it difficult to apply general ‘rules-of-thumb’ for conservation actions. This is particularly true in dendritic networks, where habitat connections are constrained.
2. By constructing a metapopulation model that specifically accounts for the unique characteristics and ecological system of a target species, the relative influence of local population characteristics and habitat connectivity on metapopulation persistence can be assessed more accurately.
3. This modelling approach was used to improve conservation outcomes for the Canterbury mudfish (kо̄waro Neochanna burrowsius), a critically endangered and poorly understood species that is endemic to the Canterbury Plains of Aotearoa/New Zealand. A spatially structured metapopulation model of N. burrowsius was used to investigate the relationship between habitat patch connectivity, rate of population growth as limited by habitat quality (r_conditional), and metapopulation persistence.
4. N. burrowsius metapopulation persistence increased most strongly under increases in r_conditional, but increases in habitat connectivity also had positive effects (94% metapopulation persistence for highly connected networks vs. 39% metapopulation persistence for poorly connected networks where r_conditional = 1.3).
5. Although rates of population growth were more influential than increases in habitat connectivity in this case study, both will be important to consider for effectively allocating conservation resources for metapopulations in dendritic networks, depending on what managers could effectively manipulate to enhance metapopulation persistence.

     

Status of the hammerhead shark (Carcharhiniformes: Sphyrnidae) fishery in Indian waters with observations on the biology of scalloped hammerhead Sphyrna lewini (Griffith & Smith, 1834)

1. Hammerhead sharks are represented by four species in India's marine fishery – Sphyrna lewini, Sphyrna mokarran, Sphyrna zygaena and Eusphyra blochii. This paper describes the hammerhead shark fishery in India during 2007–2018 and summarizes observations on the biology of S. lewini exploited along the Indian coast.
2. Hammerhead sharks are caught by trawl nets, gillnets, seines and line gear, mostly as bycatch. Annual average landing of hammerhead sharks during 2007–18 was 639 t, with a low of 290 t in 2018, of which S, lewini was the dominant species, comprising 95% of landings. Hammerhead sharks formed nearly 1.31% of the total elasmobranch landings. About 54% of hammerhead sharks were landed by trawlers.
3. Length range of S. lewini in regular landings was 36–300 cm total length (TL). The dominant size class was 30–100 cm TL; 79.5% of males and 83.2% of females measured between 40 and 100 cm TL. Length–weight relationship was derived as W = 0.0218*(L)^2.634 and W = 0.0131*(L)^2.769 for males and females, respectively.
4. Overall sex ratio (F: M) was 1.3:1; below 100 cm TL, the sex ratio was skewed in favour of females. The length at first maturity of males was estimated as 168 cm. The length at first maturity of females was estimated at 239.6 cm. Fecundity ranged from 12–40, size at birth was 36–45 cm TL. Bony fishes were the preferred prey, followed by cephalopods.
5. The S. lewini landings in India are dominated by juveniles and threatens sustainability of the stock. Capture of juvenile sharks can be excluded to a considerable extent through strict implementation of minimum legal size of capture, and a conservative minimum legal size of 220 cm is suggested for this species in Indian waters. Identification of recurring juvenile aggregation grounds, their spatio-temporal closures, gear restrictions and greater stakeholder awareness could lead to conservation of the resource and a sustainable fishery.

     

Global population genetic structure of the sequential hermaphrodite,dusky grouper (Epinephelus marginatus)

1. The dusky grouper Epinephelus marginatus is a large epinephelid species that occurs in the eastern and south-western Atlantic and western Indian Oceans. Late maturity, protogynous hermaphroditism, site fidelity, and overfishing have all contributed to its demographic decline.
2. Connectivity and demography within a broad sampling of dusky grouper populations throughout its distribution were assessed. To do so, genetic variation at 11 polymorphic microsatellite loci and a partial sequence of the mitochondrial control region (mtCR) were evaluated.
3. Two major mtCR lineages with a sequence divergence of 1.6% were found. The magnitude of genetic differentiation for mtCR among north and south Atlantic and Indian Ocean populations was high, with Φ_ST = 0.528.
4. D_EST and results of discriminant analysis of principal component revealed significant microsatellite genetic differentiation between all collection areas. Significant pairwise D_EST showed moderate (0.084) to very great (0.603) differentiation. The effective population size was low for all localities, ranging between 25 (Azores Archipelago) and 311 (Rio Grande do Sul). The overall effective population size was estimated as 299 (confidence interval = 215–412), and there was no evidence of strong or recent bottleneck effects.
5. Local and regional genetic structuring among dusky grouper populations is the consequence of the species' site fidelity, distribution across multiple oceanographic boundaries, and probably also of sequential hermaphroditism that contributes to the intensity of random genetic drift.
6. The spatial pattern of genetic structuring of dusky groupers is such that fisheries management and conservation of population genetic integrity will have to be pursued at the local and regional scales.