Viability of the vaquita, Phocoena sinus (Cetacea: Phocoenidae) population, threatened by poaching of Totoaba macdonaldi (Perciformes: Sciaenidae) / Viabilidad de la población de vaquita marina, Phocoena sinus (Cetacea: Phocoenidae), amenazada por la pesca ilegal de Totoaba macdonaldi (Perciformes: Sciaenidae)

Abstract Introduction: Despite extensive science-based conservation policy recommendations, with fewer than 20 individuals remaining, the vaquita (Phocoena sinus) -endemic to the Gulf of California- is the world's most endangered marine mammal due to incidental catch in fishing nets and whether it can recover is unclear. Objective: Assess expectations for vaquita over the next two decades. Methods: We identified factors affecting the vaquita, constructed life tables, derived demographic parameters for different scenarios and conducted a population viability analysis using stochastic age-structured matrix Leslie models. Results: Analytical results indicate that the vaquita net growth rate is particularly sensitive to juvenile survival. We find that intensive, ongoing bycatch in gillnets used to poach totoaba (Totoaba macdonaldi) over the past decade brought the vaquita population to its current critically low size. Currently this seems to be exacerbated by demographic stochasticity and a potential Allee effect. Conclusions: If totoaba poaching is eliminated immediately, demographically, vaquita can recover; its long-term survival will depend on its uncertain genetic status, although a recent study found encouraging results in this regard.

Resumen Introducción: Pese a las acciones de conservación basadas en la ciencia y las políticas recomendadas, con menos de 20 individuos sobrevivientes, la vaquita (Phocoena sinus) -endémica del Golfo de California- es el mamífero marino más amenazado del mundo debido a su muerte incidental en redes de pesca; una pregunta relevante es si su población se puede recuperar. Objetivo: Evaluar las expectativas para la vaquita marina durante los próximos 20 años. Métodos: Identificamos los factores que afectan a la vaquita marina, construimos tablas de vida, derivamos parámetros demográficos para diferentes escenarios y realizamos un análisis de viabilidad poblacional utilizando matrices estocásticas de Leslie, estructuradas por edad. Resultados: La tasa de crecimiento neto de la vaquita es muy sensible a la supervivencia de los juveniles. Encontramos que la captura incidental intensiva y continua en redes de enmalle para la pesca furtiva de totoaba (Totoaba macdonaldi) durante la última década llevó a la población de vaquitas a su actual estado crítico. Esto parece agravarse por la estocasticidad demográfica y un potencial efecto Allee. Conclusiones: Si la pesca furtiva de totoaba se elimina de inmediato, demográficamente la vaquita puede recuperarse; su supervivencia a largo plazo dependerá de su incierto estatus genético, aunque los resultados de un estudio reciente son alentadores en este sentido.

Impact of minimum catch size on the population viability of Strombus gigas (Mesogastropoda: Strombidae) inQuintana Roo, Mexico / Impacto de la talla mínima de captura en la viabilidad de la población de Strombus gigas (Mesogastropoda: Strombidae) en Quintana Roo, Mexico

The queen conch Strombus gigas represents one of the most important fishery resources of the Caribbean but heavy fishing pressure has led to the depletion of stocks throughout the region, causing the inclusion of this species into CITES Appendix II and IUCN’s Red-List. In Mexico, the queen conch is managed through a minimum fishing size of 200mm shell length and a fishing quota which usually represents 50% of the adult biomass. The objectives of this study were to determine the intrinsic population growth rate of the queen conch population of Xel-Ha, Quintana Roo, Mexico, and to assess the effects of a regulated fishing impact, simulating the extraction of 50% adult biomass on the population density. We used three different minimum size criteria to demonstrate the effects of minimum catch size on the population density and discuss biological implications. Demographic data was obtained through capture-mark-recapture sampling, collecting all animals encountered during three hours, by three divers, at four different sampling sites of the Xel-Ha inlet. The conch population was sampled each month between 2005 and 2006, and bimonthly between 2006 and 2011, tagging a total of 8 292 animals. Shell length and lip thickness were determined for each individual. The average shell length for conch with formed lip in Xel-Ha was 209.39±14.18mm and the median 210mm. Half of the sampled conch with lip ranged between 200mm and 219mm shell length. Assuming that the presence of the lip is an indicator for sexual maturity, it can be concluded that many animals may form their lip at greater shell lengths than 200mm and ought to be considered immature. Estimation of relative adult abundance and densities varied greatly depending on the criteria employed for adult classification. When using a minimum fishing size of 200mm shell length, between 26.2% and up to 54.8% of the population qualified as adults, which represented a simulated fishing impact of almost one third of the population. When conch extraction was simulated using a classification criteria based on lip thickness, it had a much smaller impact on the population density. We concluded that the best management strategy for S. gigas is a minimum fishing size based on a lip thickness, since it has lower impact on the population density, and given that selective fishing pressure based on size may lead to the appearance of small adult individuals with reduced fecundity. Furthermore, based on the reproductive biology and the results of the simulated fishing, we suggest a minimum lip thickness of ≥15mm, which ensures the protection of reproductive stages, reduces the risk of overfishing, leading to non-viable density reduction. Rev. Biol. Trop. 62 (4): 1343-1352. Epub 2014 December 01.

El caracol rosa Strombus gigas representa una de las especies de mayor importancia pesquera en el Caribe, pero la creciente presión pesquera ha llevado al deterioro de las poblaciones en toda la región, llevando a la inclusión de esta especie en el apéndice II de CITES y la lista roja de UICN. En México, el caracol rosa se maneja con una talla mínima de pesca de 200mm longitud de heliconcha y una cuota pesquera que generalmente representa el 50% de la biomasa adulta. Este estudio tuvo como objetivos determinar la tasa intrínseca de crecimiento poblacional del caracol rosa en Xel-Ha, Quintana Roo, México, y evaluar el efecto de un esfuerzo pesquero regulado, simulando la extracción del 50% de la biomasa adulta. Utilizamos tres diferentes criterios de talla mínima para la pesca, para evaluar el efecto de ésta sobre la densidad de la población y discutimos las implicaciones bilógicas asociadas. Los datos demográficos se obtuvieron mediante un muestreo de marcaje-recaptura, recolectando todos los animales presentes, durante tres horas, con tres buzos, en cuatro sitios diferentes de la caleta. En 2005 los muestreos fueron mensuales, y de 2006 a 2011 bimensuales, marcándose un total de 8 292 caracoles. Se obtuvo la longitud de heliconcha y grosor de labio de cada individuo. La talla media de caracoles con labio formado fue de 209.39±14.18mm y la mediana de 210mm. La mitad de los caracoles con un labio formado presentaban tallas de 200mm a 219mm longitud de heliconcha. Suponiendo que la presencia del labio es un indicador de madurez sexual, se puede concluir que muchos animales alcanzan la madurez sexual a tallas mayores de 200mm longitud de heliconcha y deberían ser considerados inmaduros. La estimación de la abundancia relativa y densidad de adultos varía ampliamente según el criterio de clasificación utilizado. Cuando se aplicó una talla mínima de 200mm longitud, el 26.2% a 54.8% de la población calificó como adulta, correspondiendo a un impacto pesquero simulado de casi un tercio de la población. El impacto fue menor simulando la extracción de adultos, utilizando un criterio de clasificación basado en grosor de labio. Se concluyó que la mejor estrategia de manejo para S. gigas es una talla mínima basada en el grosor de labio, ya que esta medida reduce el impacto sobre la densidad poblacional, y por el otro lado disminuye la presión selectiva sobre la talla, lo cual conduce a la aparición de individuos pequeños con fecundidad inferior. Más allá, basado en la biología reproductiva y los resultados de las simulaciones, recomendamos un grosor de labio mínimo de ≥15mm para la pesca, ya que esta medida asegura la protección de las etapas reproductivas y reduce el riesgo de sobrepesca, el cual llevaría a reducciones no viables de la densidad poblacional.

Does adaptive strategy for delayed seed dispersion affect extinction probability of a desert species? an assessment using the population viability analysis and glass house experiment

Canopy seed bank is an important adaptive evolutionary trait that provides various types of protection to the seeds. However, costing of such evolutionary trait on plant survival is largely unknown. Present investigation provided a new insight on the serotonious habit of Blepharis sindica associated with its endangerment status. Extinction probabilities of two available population of B. sindica were quantified using two types of census data, i.e., fruiting body number and actual population size. Population Viability Analysis (PVA) revealed that delayed seed release tendency (higher fruiting body number) was not synchronized with actual ground conditions (lower population size). PVA analysis based on actual population size indicated that both the available populations would vanish within 20 years. The mean time of extinction calculated from both type census data indicated its extinction within 48 years. For assessing the conservation criteria, a glass house experiment was carried out with different soil types and compositions. Pure sand and higher proportions of sand -silt were more suitable compared to clay; further, gravelly surface was the most unsuitable habitat for this species. Collection of the seeds from mature fruits/capsule and their sowing with moderate moisture availability with sandy soil could be recommended.

Extinction of mammalian populations in conservation units of the Brazilian Cerrado by inbreeding depression in stochastic environments

Despite methodological and theoretical advances in conservation genetics, data on genetic variation on broad regional spatial scales are still scarce, leading conservation planners to use general heuristic or simulation models for an integrated analysis of genetic, demographic and landscape parameters. Here, we extended previous results by evaluating spatial patterns of extinction by inbreeding depression under stochastic variation of environments for mammalian populations in 31 conservation units of the Brazilian Cerrado. We observed a large spatial variation of times to extinction, for different conservation units and body-size classes of species. For small-bodied species (500 g), the population times to extinction in the conservation units were usually longer than 200 years, whereas for medium-bodied (5 kg) and large-bodied (50 kg) species this time was considerably shorter, and only a few units would maintain viable populations for more than 100 years. These figures are consistent with the current status of mammalian conservation in Brazil, and hopefully the simulated scenarios can be integrated to patterns of human occupation and habitat loss in the biome, in order to furnish overall guidelines for biodiversity conservation.