A NEW ABUNDANCE ESTIMATE FOR VAQUITAS: FIRST STEP FOR RECOVERY1

A line-transect survey specifically designed to estimate vaquita (Phocoena sinus) abundance over its entire range was carried out by three boats in the summer of 1997. There was a total of 125 sightings of vaquita groups, mainly due to the use of large 25 ± 150 binoculars, which were seven times more effective in detecting vaquitas than hand-held 7 ± binoculars. Results confirmed that the range of the vaquita is restricted to the northwestern corner of the Gulf of California, Mexico, but that the boundaries of the Upper Gulf of California and Colorado River Delta Biosphere Reserve do not correspond well with the distribution of vaquitas. The shallow water north of the town of San Felipe was found to have a higher density of animals than had been indicated by previous surveys. The total population size was estimated to be 567 animals, with a 95% confidence interval from 177 to 1,073. This estimate is an improvement over previous estimates, which had low numbers of sightings, relied on parameters taken from other species, and/or did not cover all areas where vaquitas could potentially be found. The 1997 estimate was more than twice the 1993 estimate, but there are several reasons why the numbers cannot be directly compared, and it should not be concluded the population is increasing. This first complete estimate of vaquita abundance can be a beginning for the recovery of this highly endangered species.     

Exploring Trade-Offs between Fisheries and Conservation of the Vaquita Porpoise (Phocoena sinus) Using an Atlantis Ecosystem Model

Background

Minimizing fishery bycatch threats might involve trade-offs between maintaining viable populations and economic benefits. Understanding these trade-offs can help managers reconcile conflicting goals. An example is a set of bycatch reduction measures for the Critically Endangered vaquita porpoise (Phocoena sinus), in the Northern Gulf of California, Mexico. The vaquita is an endemic species threatened with extinction by artisanal net bycatch within its limited range; in this area fisheries are the chief source of economic productivity.

Methodology/Principal Findings

We analyze trade-offs between conservation of the vaquita and fisheries, using an end-to-end Atlantis ecosystem model for the Northern Gulf of California. Atlantis is a spatially-explicit model intended as a strategic tool to test alternative management strategies. We simulated increasingly restrictive fisheries regulations contained in the vaquita conservation plan: implementing progressively larger spatial management areas that exclude gillnets, shrimp driftnets and introduce a fishing gear that has no vaquita bycatch. We found that only the most extensive spatial management scenarios recovered the vaquita population above the threshold necessary to downlist the species from Critically Endangered. The scenario that excludes existing net gear from the 2008 area of vaquita distribution led to moderate decrease in net present value (US$ 42 million) relative to the best-performing scenario and a two-fold increase in the abundance of adult vaquita over the course of 30 years.

Conclusions/Significance

Extended spatial management resulted in the highest recovery of the vaquita population. The economic cost of proposed management actions was unequally divided between fishing fleets; the loss of value from finfish gillnet fisheries was never recovered. Our analysis shows that managers will have to confront difficult trade-offs between management scenarios for vaquita conservation.     

Conservation of the vaquita Phocoena sinus

• 1 The vaquita Phocoena sinus is a small porpoise that is endemic to the northern Gulf of California, Mexico. It is the most critically endangered marine small cetacean in the world. The most precise estimate of global abundance based on a 1997 survey is 567 (95% CI 177–1073).
• 2 Vaquitas mainly live north of 30°45′N and west of 114°20′W. Their ‘core area’ consists of about 2235 km² centred around Rocas Consag, 40 km east of San Felipe, Baja California. Genetic analyses and population simulations suggest that the vaquita has always been rare, and that its extreme loss of genomic variability occurred over evolutionary time rather than being caused by human activities.
• 3 Gill nets for fish and shrimp cause very high rates of by‐catch (entanglement) of vaquitas. Estimates of bycatch rates are from 1993–94 and refer to one of three main fishing ports: 84 per year (95% CI 14–155) using only data collected by observers and 39 per year (95% CI 14–93) using combined data from observers and interviews with fishermen. Boats from other ports may experience similar rates, and the total is probably well above what would be sustainable.
• 4 Other less well‐characterized and longer‐term risk factors include the potential for disturbance by trawling to affect vaquita behaviour, and the uncertain effects of dam construction on the Colorado River and the resultant loss of freshwater input to the upper Gulf. However, entanglement is the clearest and most immediate concern.
• 5 Progress towards reducing entanglement has been slow in spite of efforts to phase out gill nets in the vaquita’s core range, and the development of schemes involving compensation for fishermen. The Biosphere Reserve in the northern Gulf has fallen far short of its potential for vaquita conservation. On 29 December 2005, the Mexican Ministry of Environment declared a Vaquita Refuge that contains within its borders the positions of approximately 80% of verified vaquita sightings. In the same decree, the state governments of Sonora and Baja California were offered $1 million to compensate affected fishermen. The effectiveness of this major initiative remains to be seen.
• 6 The vaquita’s survival does not depend on more or better science but on improved management. As a funding priority, implementation of conservation measures and evaluation of their effectiveness should come ahead of more surveys or improved estimation of by‐catch.

     

EXAMINING THE RISK OF INBREEDING DEPRESSION IN A NATURALLY RARE CETACEAN,THE VAQUITA (PHOCOENA SINUS)1

Uncertainty about the magnitude of various risks facing endangered species can paralyze conservation action. The vaquita is a naturally rare porpoise that has declined to the low hundreds of individuals because of gillnet mortality over the past 57 years. No variability in mitochondrial DNA (mtDNA) was found in vaquitas (n= 43). Because reducing gillnet mortality will require strong conservation action, the question was raised whether vaquitas are doomed because of inbreeding depression and whether, therefore, mitigation efforts would be futile. We use simulations to investigate the “doom hypothesis” by first asking whether the current level of genetic variability results from the recent decline or from historical factors. If fixation was historical then deleterious alleles could have been selected out of vaquitas over thousands of years, reducing concerns about inbreeding depression. Simulations showed that fixation most likely resulted from historical rather than recent loss. Of 1,000 simulations done at plausible abundances and mutation rates, 247 (84.3%) fixed before and 46 (15.7%) fixed during the recent decline. Fixation correlates with historical abundance, making it more likely that because vaquitas are fixed, they are also a naturally rate species. However, because studies on purging deleterious alleles have not shown purging to be universally beneficial we also examine the doom hypothesis using data on the response to inbreeding of a wide variety of captive animals. Responses are so variable that the doom hypothesis cannot be affirmed. We further explore whether more data from vaquitas would lead to conclusive results and found that the data required, such as the adult survival rate, will be impossible to obtain. We conclude that because the doom hypothesis cannot be affirmed this risk factor should not delay conservation actions.     

MITOCHONDRIAL DNA VARIATION IN THE CRITICALLY ENDANGERED VAQUITA PHOCOENA SINUS NORRIS AND MACFARLAND, 19581

The vaquita, Phocoena sinus, is one of two critically endangered cetacean species, and is listed as an endangered species in both the United States and Mexico. These listings result from a small population size, estimated to be 224 animals, and a rapid decline in abundance (18% per annum) thought to be caused by human activities. To characterize the genetic composition of the vaquita, we have sequenced a portion of the mitochondrial DNA control region from 43 individuals collected between 1985 and 1993. All animals had identical sequences. While low genetic variability has been reported for cetacean species, this complete lack of polymorphism in the control region is unique. This result is concordant with the hypothesis that the evolutionary history of the species includes a bottleneck or founder event, possibly at species inception, followed by a small long-term effective population size. We recommend parallel studies of nuclear variability, which could provide understanding of the basic biology of the vaquita for use in conservation efforts.     

Managing genetic diversity in threatened populations: a New Zealand perspective

Genetic diversity allows a population to adapt genetically to a changing environment or to buffer it against stochastic events such as harsh weather or disease outbreaks. Genetic diversity is therefore an important consideration in the development of management strategies for threatened populations around the world, with the possible exception of New Zealand, where species recovery programmes tend to focus on increasing population size while neglecting the maintenance of genetic diversity. Many of New Zealand?s threatened species have relatively low genetic variation and consequently may still be at risk in the long-term due to reduced resilience even if the effects of introduced predators were eliminated. The three main factors affecting genetic diversity – genetic drift, inbreeding and population subdivision – are processes that potentially impact on many of our locally threatened species, but their effects tend to occur over a considerably broader timescale than ecological effects, and as such are much more difficult to detect and ultimately to justify additional resource spending towards. Our message is that genetic management of New Zealand threatened species should not take priority over other management concerns such as controlling predators or improving habitat quality, but it needs more attention than it currently receives. We recommend that genetic diversity be a fundamental component in long-term management strategies for threatened species, and that such strategies are made explicit within the New Zealand Department of Conservation?s current species recovery plans so that the persistence of biodiversity becomes of key importance, as opposed to current approaches that seek solely to maximise representation.     

The Ecological Role of the Vaquita, Phocoena sinus, in the Ecosystem of the Northern Gulf of California

From an ecosystem management perspective, analysis of the functional roles of species is a challenge. It is valuable to determine which species are irreplaceable within a given community based on their contribution to the system’s organization. This study relates the emergent functional and structural indices of biological groups estimated from a trophic model of the Northern Gulf of California to identify the roles of these groups in the ecosystem context, with a particular focus on the role of the vaquita, an endemic porpoise in critically endangered status. The simulation of removing each group allowed the analysis of the removal’s functional effect on the ecosystem’s global attributes and organization (based on Ulanowicz’s ascendency concept). Groups from lower trophic levels (TL) were more related to complexity indicators, suggesting their contribution to the organization and structure of energy flows in the food web. Groups from intermediate TL had higher values of structural indexes, indicating their function in the control of flows throughout the network. The vaquita along with other marine mammals, aquatic birds, and some species of fish with a high TL contribute in a similar way to the order (for example, ascendency/capacity-of-development ratio) of the system, showing a relatively high value of ascendency (contribution of the group to the organization inherent to the ecosystem) and the change in ecosystem ascendency when they were removed. The vaquita, like marine and coastal birds, plays a small role in the ecosystem. But like them, it does contribute substantially to ecosystem organization. This study thus provides information potentially useful for management in understanding the species’ role and in reducing uncertainty in decision-making.     

Uncertainty in research about key invasion characteristics limits the evaluation of exotic perennial grasses in natural systems in New South Wales,Australia

Exotic perennial grasses (EPGs) pose a significant risk to native communities globally. With over 2,200 species in Australia, understanding which characteristics enable high threat invasions, and comparing between functionally similar EPGs, can help prioritise species management. We developed a framework of risk and used the literature to rank 21 EPGs considered a threat to plant communities in New South Wales, while also evaluating the reliability of information currently available. Characteristics were scored within five broad categories that distinguish invasiveness: Arrival, Establishment, Persistence, Impact and Distribution. These included aspects of reproductive biology, competitive ability and environmental tolerance. The risk assessment was effective in assessing key characteristics of invasion. EPGs with an economic benefit (trade‐off species) were more likely to have reliable research and frequently ranked as high‐risk invaders in natural habitats due to the overlap of characteristics important in invasion with those considered important in agriculture. Lack of formal scientific research hindered assessment for some species, and some traits had been poorly assessed in the literature. High uncertainty was associated with key characteristics for Establishment, Persistence and Impact. Uncertainty in key characteristics revealed a need for improved integration of less formal research validated by more formal scientific research. This may lead to more informed decisions in the management of EPGs in native habitats and assist in early control of EPGs not yet assessed.     

C-reactive protein as a prognostic tool in cardiovascular practices: should CRP testing be ordered along with lipid profiles?

CRP has a graded, dose-response relationship to the occurrence of clinical cardiovascular events that remains after adjustment for other risk factors, with moderately strong associations between the lower and upper tertiles (RR≈2). It may have clinical utility in improving the estimation of absolute risks of patients with a calculated ten-year risk between 10 and 20%. Individuals at low risk (<10% per 10 years) will be unlikely to have a high risk identified through CRP testing. Additional prospective studies or new statistical analysis of previous studies are needed to establish the added predictive value of CRP above that of currently established risk factors. Thus, currently available evidence suggests that CRP testing should not be ordered along with lipid profiles.     

Genetic drift vs. natural selection in a long-term small isolated population: major histocompatibility complex class II variation in the Gulf of California endemic porpoise (Phocoena sinus)

Although many studies confirm long-term small isolated populations (e.g. island endemics) commonly sustain low neutral genetic variation as a result of genetic drift, it is less clear how selection on adaptive or detrimental genes interplay with random forces. We investigated sequence variation at two major histocompatibility complex (Mhc) class II loci on a porpoise endemic to the upper Gulf of California, México (Phocoena sinus, or vaquita). Its unique declining population is estimated around 500 individuals. Single-strand conformation polymorphism analysis revealed one putative functional allele fixed at the locus DQB (n = 25). At the DRB locus, we found two presumed functional alleles (n = 29), differing by a single nonsynonymous nucleotide substitution that could increase the stability at the dimer interface of alphabeta-heterodimers on heterozygous individuals. Identical trans-specific DQB1 and DRB1 alleles were identified between P. sinus and its closest relative, the Burmeister's porpoise (Phocoena spinipinnis). Comparison with studies on four island endemic mammals suggests fixation of one allele, due to genetic drift, commonly occurs at the DQA or DQB loci (effectively neutral). Similarly, deleterious alleles of small effect are also effectively neutral and can become fixed; a high frequency of anatomical malformations on vaquita gave empirical support to this prediction. In contrast, retention of low but functional polymorphism at the DRB locus was consistent with higher selection intensity. These observations indicated natural selection could maintain (and likely also purge) some crucial alleles even in the face of strong and prolonged genetic drift and inbreeding, suggesting long-term small populations should display low inbreeding depression. Low levels of Mhc variation warn about a high susceptibility to novel pathogens and diseases in vaquita.     

The risk of invasion by angiosperms peaks at intermediate levels of human influence

Biological invasions are a growing threat to biodiversity. The control and eradication of exotic species established in earnest are of limited success despite high financial investments. Anticipating biological invasions based on species’ suitabilities is a cost-effective strategy given it helps identifying areas where exotic species can prosper, which can then translate in improving management and conservation efforts. Based on information from 191 invasive angiosperm species worldwide, we used ecological niche models to identify areas at high risk of invasion (cumulative predicted distribution of invasive species) in Mexico. Further, we explored the importance of bioclimatic and human influence variables as drivers of the distribution of invasive species and analyzed the status of the currently recognized priority conservation sites in Mexico. We found that areas with intermediate human activity scores had a high risk of invasion. Additionally, we found that many of the current priority conservation sites in Mexico had a high risk of invasion. Our findings contribute to disentangling the factors that drive environment susceptibility to invasions and urge management strategies to minimize the impacts of biological invasions in priority conservation sites.     

The predation risks of interspecific eavesdropping: weasel–vole interactions

Competing species benefit from eavesdropping on each other's signals by learning about shared resources or predators. But conspicuous signals are also open to exploitation by eavesdropping predators and should also pose a threat to other sympatric prey species. In western Finland, sibling voles Microtus rossiameridionalis and field voles M. agrestis compete for food and space, and both species rely upon scent marks for intraspecific communication. Both vole species are prey to a range of terrestrial scent hunting predators such as least weasels, however, the competitively superior sibling voles are taken preferentially. We tested in large out‐door enclosures whether field voles eavesdrop on the signals of its competitor, and whether they behave as though this eavesdropping carries a risk of predation. We presented field voles with scent marks from unknown conspecifics and sibling voles and measured their visitation, activity and scent marking behaviours at these scents under high (weasel present) and low (weasel absent) predation risk. Field voles readily visited both field and sibling vole scents under both high and low predation risk; however their activity at sibling vole scent marks declined significantly under increased predation risk. In contrast, predation risk did not affect field voles’ activity at conspecific scents. Thus, field voles were compelled to maintain eavesdropping on heterospecific scents under an increased risk of predation, however they compensated for this additional risk by reducing their activity at these risky scents. Scent marking rates declined significantly under high predation risk. Our results therefore reveal a hidden complexity in the use of social signals within multi‐species assemblages that is clearly sensitive to the potential for increased predation risk. The predation risks of interspecific eavesdropping demonstrated here represents a significant generalisation of the concept of associational susceptibility.     

Quantifying components of risk for European woody species under climate change

Estimates of species extinction risk under climate change are generally based on differences in present and future climatically suitable areas. However, the locations of potentially suitable future environments (affecting establishment success), and the degree of climatic suitability in already occupied and new locations (affecting population viability) may be equally important determinants of risk. A species considered to be at low risk because its future distribution is predicted to be large, may actually be at high risk if these areas are out of reach, given the species' dispersal and migration rates or if all future suitable locations are only marginally suitable and the species is unlikely to build viable populations in competition with other species. Using bioclimatic models of 17 representative European woody species, we expand on current ways of risk assessment and suggest additional measures based on (a) the distance between presently occupied areas and areas predicted to be climatically suitable in the future and (b) the degree of change in climatic suitability in presently occupied and unoccupied locations. Species of boreal and temperate deciduous forests are predicted to face higher risk from loss of climatically suitable area than species from warmer and drier parts of Europe by 2095 using both the moderate B1 and the severe A1FI emission scenario. However, the average distance from currently occupied locations to areas predicted suitable in the future is generally shorter for boreal species than for southern species. Areas currently occupied will become more suitable for boreal and temperate species than for Mediterranean species whereas new suitable areas outside a species' current range are expected to show greater increases in suitability for Mediterranean species than for boreal and temperate species. Such additional risk measures can be easily derived and should give a more comprehensive picture of the risk species are likely to face under climate change.     

Distribution models of invasive plants over-estimate potential impact

Habitat suitability models developed for non-native, invasive species often implicitly assume that projected invasion risk equates to risk of impact. I aim to test to what extent this assumption is true by comparing commonly-used invasive plant distribution datasets to abundance records. I compared herbarium occurrence records (downloaded from an online database) and regional occurrence records (compiled from individual states) to abundance estimates collected from over 300 invasive plant experts for 9 invasive species in the western U.S. I also created habitat suitability models (HSMs) using these datasets and compared the areas of predicted suitability. Sixty percent of the time, herbarium occurrences were located in regions where the species was rare enough to be undetected by experts, while only 26 % coincided with locations identified as having high abundance. Regional occurrences were located in areas where the species was not detected 32 % of the time, and on high abundance 42 % of the time. HSMs based on herbarium records encompassed 89 % of land area at risk of abundance, but overestimated the area of estimated risk (27–46 % false positive rate). HSMs based on regional occurrences had a smaller false positive rate (22–31 %), but encompassed only 67–68 % of area suitable for abundance. Herbarium records are strongly skewed towards locations with low invasive plant abundance, leading to invasion risk models that vastly overestimate abundance risk. Models based on occurrence points should be interpreted as risk of establishment only, not risk of abundance or impact. If HSMs aim to be more management relevant, invasion risk models should include abundance as well as occurrence.     

Extinction processes in hot spots of avian biodiversity and the targeting of pre-emptive conservation action

Hot spots of endemism are regarded as important global sites for conservation as they are rich in threatened endemic species and currently experiencing extensive habitat loss. Targeting pre-emptive conservation action to sites that are currently relatively intact but which would be vulnerable to particular human activities if they occurred in the future is, however, also valuable but has received less attention. Here, we address this issue by using data on Endemic Bird Areas (EBAs). First, we identify the ecological factors that affect extinction risk in the face of particular human activities, and then use these insights to identify EBAs that should be priorities for pre-emptive conservation action. Threatened endemic species in EBAs are significantly more likely to be habitat specialists or relatively large-bodied than non-threatened species, when compared across avian families. Increasing habitat loss causes a significant increase in extinction risk among habitat specialists, but we found no evidence to suggest that the presence of alien species/human exploitation causes a significant increase in extinction risk among large-bodied species. This suggests that these particular human activities are contributing to high extinction risk among habitat specialists, but not among large-bodied species. Based on these analyses, we identify 39 EBAs containing 570 species (24% of the total in EBAs) that are not currently threatened with severe habitat loss, but would be ecologically vulnerable to future habitat loss should it occur. We show that these sites tend to be poorly represented in existing priority setting exercises involving hot spots, suggesting that vulnerability must be explicitly included within these exercises if such sites are to be adequately protected.     

Prediction and validation of the potential global distribution of a problematic alien invasive species — the American bullfrog

Predicting the probability of successful establishment and invasion of alien species at global scale, by matching climatic and land use data, is a priority for the risk assessment. Both large- and local-scale factors contribute to the outcome of invasions, and should be integrated to improve the predictions. At global scale, we used climatic and land use layers to evaluate the habitat suitability for the American bullfrog Rana catesbeiana , a major invasive species that is among the causes of amphibian decline. Environmental models were built by using Maxent, a machine learning method. Then, we integrated global data with information on richness of native communities and hunting pressure collected at the local scale. Global-scale data allowed us to delineate the areas with the highest suitability for this species. Predicted suitability was significantly related to the invasiveness observed for bullfrog populations historically introduced in Europe, but did not explain a large portion of variability in invasion success. The integration of data at the global and local scales greatly improved the performance of models, and explained > 57% of the variance in introduction success: bullfrogs were more invasive in areas with high suitability and low hunting pressure over frogs. Our study identified the climatic factors entailing the risk of invasion by bullfrogs, and stresses the importance of the integration of biotic and abiotic data collected at different spatial scales, to evaluate the areas where monitoring and management efforts need to be focused.     

Predicted versus actual invasiveness of climbing vines in Florida

Climbing vines cause substantial ecological and economic harm, and are disproportionately represented among invasive plant species. Thus, the ability to identify likely vine invaders would enhance the effectiveness of both prevention and management. We tested whether the Weed Risk Assessment (WRA) accurately predicted the current invasion status of 84 non-native climbing vines in Florida. Seventeen percent of the species require further evaluation before risk of invasion can be determined. Of the remaining 70 species, the WRA predicted that 70% were at high risk for invasion, but only 50% of the 84 species are currently invasive in Florida. The status and risk prediction were inconsistent for 27% of the species: 15 non-invaders were predicted to be of high risk for invasion (i.e., false positive) and 4 invaders were predicted to be of low risk (i.e., false negative). Longer residence time in the flora was significantly correlated with higher invasion risk. Further investigation is necessary to identify whether residence time explains inconsistencies between risk and status conclusions, or whether the WRA over-predicts invasion risk. Nevertheless, the effects of invasive vines on native systems coupled with the influence of time on invasion status, suggest a precautionary approach is warranted when considering the introduction and management of non-native vines.     

Assessing the port to port risk of vessel movements vectoring non-indigenous marine species within and across domestic Australian borders

Biofouling of vessels is implicated as a high risk transfer mechanism of non-indigenous marine species (NIMS). Biofouling on international vessels is managed through stringent border control policies, however, domestic biofouling transfers are managed under different policies and legislative arrangements as they cross internal borders. As comprehensive guidelines are developed and increased compliance of international vessels with 'clean hull' expectations increase, vessel movements from port to port will become the focus of biosecurity management. A semi-quantitative port to port biofouling risk assessment is presented that evaluates the presence of known NIMS in the source port and determines the likelihood of transfer based on the NIMS association with biofouling and environmental match between source and receiving ports. This risk assessment method was used to assess the risk profile of a single dredge vessel during three anticipated voyages within Australia, resulting in negligible to low risk outcomes. This finding is contrasted with expectations in the literature, specifically those that suggest slow moving vessels pose a high to extreme risk of transferring NIMS species.     

Identifying critical habitat of the endangered vaquita (Phocoena sinus) with regional δ13C and δ15N isoscapes of the Upper Gulf of California,Mexico

The vaquita (Phocoena sinus) is the world's most endangered cetacean and has experienced a 60% reduction in the size of its population in the past decade. Knowledge of its basic ecology is essential for developing successful management plans to protect and conserve this species. In this study, we identified vaquita foraging areas by creating an isoscape of the Upper Gulf of California (UGC) based on sediment and zooplankton carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values. Our results confirm that this species is confined to the western region of the UGC, which is characterized by relatively high δ¹⁵N values (sediments: 10.2‰ ± 2.0‰, zooplankton: 15.8‰ ± 1.3‰), higher sea surface temperatures (～16°C–25°C), higher concentrations of silt in sediments, and the highest turbidity. In contrast, the eastern region of the UGC had relatively low sediment (7.7‰ ± 2.4‰) and zooplankton (14.6‰ ± 1.0‰) δ¹⁵N values, and the highest concentrations of sand in sediments. Our approach is an effective use of marine isoscapes over a small spatial scale (<200 km) to identify the environmental characteristics that define the critical habitat for an extremely endangered marine mammal.