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Abundance Estimates (abundance + estimate)
Selected AbstractsAt-sea distributions and abundance of tropicbirds in the eastern PacificIBIS, Issue 2 2005LARRY B. SPEAR During spring and autumn 1980,95, we surveyed Red-tailed Phaethon rubricauda, White-tailed P. lepturus and Red-billed Tropicbirds P. aethereus at sea in the Pacific between the coast of the Americas and 176°W. For the Pacific, we had complete coverage of the range of aethereus, but only partial coverage of that of rubricauda and lepturus. Six areas of higher density were indicated: three of rubricauda, two of lepturus and one of aethereus. After pooling data across years, the ,abundance' (total number including subadults and adults) estimate for rubricauda was 81 700 (boreal spring) and 86 500 (boreal autumn) birds. Abundance of each of the three rubricauda subpopulations differed between seasons by about 50% despite seasonal consistency when populations were grouped. Furthermore, high densities of rubricauda occurred at the edge of our study area, indicating that neither of the seasonal estimates for this species could be considered as total numbers. Abundance estimates of lepturus during the non-breeding season (when these birds had dispersed from colonies) were 11 000 and 41 500 birds for northern and southern populations, respectively. Estimated abundance of aethereus during the boreal spring was 26 700 birds, and 33 400 during the boreal autumn. Because tropicbirds are attracted to survey vessels, we also estimated the abundance after excluding those recorded as flying in a steady direction, or having been attracted to the ship. Considering only stationary birds (i.e. those that could not have been attracted), our minimum estimates were 41 000 rubricauda, 15 750 aethereus, 28 000 southern lepturus and 6400 northern lepturus. [source] Abundance estimates of duikers through direct counts in a rain forest, GabonAFRICAN JOURNAL OF ECOLOGY, Issue 1 2003L. Lannoy No abstract is available for this article. [source] Omnidirectional multibeam sonar monitoring: applications in fisheries scienceFISH AND FISHERIES, Issue 3 2006Patrice Brehmer Abstract Data exploitation, acquired by medium-frequency omnidirectional multibeam sonar, enables original studies in fisheries research but is seldom used despite the fact that such equipment is found on most fishing vessels and a number of research vessels. This is the only system for real-time monitoring of fish schools within a horizontal omnidirectional plane about a vessel or a buoy. Between 1996 and 2001, we used two standard omnidirectional sonars and developed new methodologies for exploiting their specific acoustic data according to two main sampling schemes: ,prospecting', including fishing and searching operations, and ,drifting', as with an instrumental buoy system or aboard a stationary vessel. We present a complete method for continuous data acquisition from aboard a research vessel or commercial boat, with automated data extraction by picture analysis and a data processing method. Two cases of data analysis are considered: the first on a school-by-school basis, the ,single school' mode; the second taking into account all fish schools detected within the sonar sampling volume, the ,cluster' mode. Elementary sonar information is divided into five categories that comprise 24 survey and sonar parameters and 55 school, cluster and fisher behaviour descriptors. We review the applications of these categories and discuss perspectives for their use in fisheries science. If the sonar system enables the evaluation of the effects of vessel avoidance on fish school biomass assessment, no accurate abundance estimate can be provided by a simple sonar echo-integration process. Omnidirectional sonar data can be used to analyse collectively the fish schools' swimming speed, kinematics in terms of diffusion and migration, aggregative dynamics as school splitting and merging indexes, spatial characteristics of clusters such as school density, 2D structure and fisher behaviour. The prospect of integrating such data into a fish school database, including multifrequency echo-sounder and lateral multibeam (3D) sonar data combined with a species recognition method, will enable a complete view of fish school behaviour and consequently the adoption of accurate fisheries management methods. [source] Effect of count duration on abundance estimates of Black-capped VireosJOURNAL OF FIELD ORNITHOLOGY, Issue 1 2009David A. Cimprich ABSTRACT Distance sampling applied to point count surveys (point transects) has become a common method for estimating the absolute abundance of birds. When conducting point transects, detections of focal species are typically recorded during a fixed time interval. However, count duration has varied among studies and the effect of such variation on the resulting abundance estimates is unclear. My objective was to examine the effect of count duration on abundance estimates of male Black-capped Vireos (Vireo atricapilla). The abundance of these vireos in a 349-ha area in central Texas was estimated using 3-, 5-, and 6-min point transects and results were then compared to actual number present as determined by banding and territory mapping. The 3-min counts provided an estimate that was 26% greater than the actual number of male Vireos present (N= 201), but this number was within the corresponding 95% confidence interval (N= 157,413). Confidence intervals for the 5- and 6-min counts did not include the actual number of vireos present. The shortest count duration may have provided the most accurate abundance estimate because male Black-capped Vireos are typically active, sing intermittently, and sometimes move tens of meters between songs. Thus, shorter-duration counts may also yield the most accurate abundance estimates for other species that exhibit similar behavior. However, because behavior varies among species, I recommend that investigators collect preliminary data to establish an appropriate count duration when accurate estimates of absolute, rather than relative, abundance are important. RESUMEN El muestreo a distancia aplicado a conteos de punto (transectos de punto) se ha convertido en un método común para estimar la abundancia absoluta de aves. Cuando se conducen conteos de punto, la detección de especies focales, típicamente, se lleva a cabo durante un periodo de tiempo definido. Sin embargo, la duración de tiempo del conteo, varía en diferentes estudios y el efecto de dicha variación, en los estimados de abundancia, no está definido. Mi objetivo fue examinar el efecto del periodo de tiempo usado en los conteos utilizando como objeto de estudio a Vireo atricapilla. La abundancia de dichas aves en 349 ha en la parte central de Texas, fue estimada utilizando periodos de 3, 5 y 6 minutos en cada punto del transecto. Los resultados fueron comparados a números obtenidos con recobro de animales anillados y mapas de territorios. Los conteos de 3 minutos dieron como resultado un 26% más alto que el número de machos presentes en la localidad (N= 201). Pero dichos resultados estuvieron dentro del intérvalo de confiabilidad de 95% (N= 157,413). Intérvalos de 5 y 6 minutos no estimaron adecuadamente el número de vireos presentes. El conteo más corto (3 minutos) suministró los números más exactos, aparentemente porque el ave estudiada, típicamente está activa, canta de forma intermitente y en ocasiones se mueve de lugar (decenas de metros) entre canciones. Por lo tanto los conteos más cortos deben de proveer los estimados de abundancia más precisos para otras especies de aves con hábitos similares. Sin embargo, dado el caso de que la conducta entre especies varía, recomendamos a otros investigadores, que tomen datos preliminares para establecer la duración más apropiada de conteos, cuando se necesiten estimados de absoluta exactitud, en vez de estimados relativos de abundancia. [source] CAPTURE-RECAPTURE ESTIMATES OF HECTOR'S DOLPHIN ABUNDANCE AT BANKS PENINSULA, NEW ZEALANDMARINE MAMMAL SCIENCE, Issue 2 2005Andrew M. Gormley Abstract Capture-recapture techniques have been extensively used to estimate survival rates of Hector's dolphins at Banks Peninsula, but not abundance. We analyzed nine seasons of photo-identification data using a model-fitting approach in the computer program MARK, and then used MARK's estimates of capture probabilities to calculate the abundance of distinctive individuals. We extrapolated these estimates to include unmarked individuals using five seasons of data on the proportion of identifiable individuals in this population, obtained from "random photography." This capture-recapture approach suggests a 1996 population of about 1,100 (CV = 0.21). This is very similar to the 1997 line-transect estimate of about 900 (CV = 0.28), especially considering that the two techniques do not necessarily measure the same thing. An important advantage of the capture-recapture approach stems from the inherent versatility of photo-ID data. If the sampling design is appropriate, an unbiased abundance estimate can be achieved as a spin-off from work directed at other questions. However, in our view, line-transect estimates are easier to interpret because the sampling design is explicit. [source] Predicting global abundance of a threatened species from its occurrence: implications for conservation planningDIVERSITY AND DISTRIBUTIONS, Issue 1 2009Marcos S. L. Figueiredo Abstract Aim, Global abundance is an important characteristic of a species that is correlated with geographical distribution and body size. Despite its importance these estimates are not available since reliable field estimates are either expensive or difficult to obtain. Based on the relationship between a species' local abundance and distribution, some authors propose that abundance can be obtained through spatial distribution data from maps plotted at different scales. This has never been tested over the entire geographical range of a species. Thus, the aim of this study was to estimate global abundance of the Neotropical primate Brachyteles hypoxanthus (northern muriqui) and compare the results with available field estimates. Location, From southern Bahia to Minas Gerais and Espírito Santo states, in the Brazilian Atlantic rain forest. Methods, We compiled 25 recent occurrence localities of B. hypoxanthus and plotted them in grid cells of five different sizes (1, 25, 50, 75 and 100 km per side) to evaluate the performance and accuracy of abundance estimates over a wide range of scales. The abundance estimates were obtained by the negative binomial distribution (NBD) method and corrected by average group size to take into account primate social habits. To assess the accuracy of the method, the predicted abundances were then compared to recent independent field estimates. Results, The NBD estimates were quite accurate in predicting B. hypoxanthus global abundance, once the gregarious habits of this species are taken into account. The predicted abundance estimates were not statistically different from those obtained from field estimates. Main conclusions, The NBD method seems to be a quick and reliable approach to estimate species abundance once several limiting factors are taken into account, and can greatly impact conservation planning, but further applications in macroecological and ecological theory testing needs improvement of the method. [source] Converting visual census data into absolute abundance estimates: a method for calibrating timed counts of a sedentary insect populationECOLOGICAL ENTOMOLOGY, Issue 4 2003Ho Jung S. Yoo Abstract., 1.,Visual surveys for small organisms on complex substrates often yield serious underestimates of true counts. When both visual counts (relative estimates of abundance) and absolute counts can be obtained from the same sample, however, the visual counts can be calibrated such that absolute estimates can be obtained in the future from visual surveys alone. 2.,A method is presented for converting quick, timed, visual counts of a sedentary insect on a shrub into absolute estimates of abundance. 3.,Analogies were drawn from simple, well-known predation theories to develop a two-parameter non-linear model. Parameter estimates were obtained by both inverse prediction and direct estimation methods; the latter were found to yield more accurate predictions of absolute abundance. 4.,The calibration model is mechanistic in its approach, and thus has potential for application in other systems in which all individuals are visible, but able to be missed during timed counts. [source] Predicting abundance from occupancy: a test for an aggregated insect assemblageJOURNAL OF ANIMAL ECOLOGY, Issue 3 2003M. Warren Summary 1The ubiquitous, positive abundance-occupancy relationship is of potential value to conservation and pest management because of the possibility of using it to predict species abundance from occupancy measures. 2He & Gaston (2000a) developed a model, and a parameterization method, for the prediction of abundance from occupancy based on the negative binomial distribution. There are to date few empirical tests of either the estimation method or model. Here we conduct such a test in a field-based mesocosm experiment using a Drosophilidae assemblage associated with decaying fruit. 3With individual (and groups of) fruit as minimum mapping units, abundance estimates derived using the parameterization method of the He-Gaston model differed significantly from measured values, and were least accurate for the most abundant species. 4Substitution of k -values corrected for species density in the model did not improve abundance predictions significantly. However, substitution of k -values calculated directly from the negative binomial distribution yielded highly accurate abundance predictions. 5Although the distribution of fly species did not deviate significantly from the negative binomial distribution, and the finest possible minimum mapping units were used (individual fruit), the parameterization method in the He-Gaston model consistently underestimated the abundance of species in the assemblage because individuals were very highly aggregated within fruit. 6Because of its potential importance, this model and parameterization method require further exploration at fine scales, commonly represented by individual habitat units, for highly aggregated species. The incorporation of spatially explicit information may provide a means of improving abundance predictions in this regard. [source] Distinguishing between the nests of sympatric chimpanzees and gorillasJOURNAL OF APPLIED ECOLOGY, Issue 2 2007CRICKETTE SANZ Summary 1Our current inability to estimate precisely the population sizes of chimpanzees and gorillas across much of the Congo Basin has been detrimental to the development of conservation strategies for the preservation of these endangered apes. Systematic counts of nests are currently the most commonly used method to estimate ape abundance, but distinguishing between the nests of sympatric chimpanzees and gorillas has proven to be an enduring obstacle to estimating species-specific abundance. In general, the builder of more than 75% of nests recorded during surveys is undetermined. We hypothesized that sleeping habits and nest building patterns would allow us to differentiate between the nests of these apes. 2We constructed a predictive model using stepwise discriminant function analysis to determine characteristics that accurately distinguished between chimpanzee and gorilla nests. We analysed 13 variables associated with 3425 ape nests from three independent surveys conducted in the Goualougo Triangle of the Nouabalé-Ndoki National Park, Republic of Congo. 3The model correctly classified more than 90% of nests in our validation subsample. Nest height, nest type, forest type and understorey closure were identified as important variables for distinguishing between chimpanzee and gorilla nests at this site. Attributing nests to either species increased the precision of resulting density estimates, which enhanced the statistical power to detect trends in population fluctuation. 4Although specific variables may differ between study sites, we have demonstrated that predictive models to distinguish between the nests of sympatric chimpanzee and gorillas provide a promising approach to improving the quality of ape survey data. 5Synthesis and applications. Our study introduces an innovative solution to the dilemma of discriminating between the nests of sympatric chimpanzees and gorillas, which increases the specificity and precision of resulting ape abundance estimates. There is an urgent need to improve methods to evaluate and monitor remaining ape populations across western and central Africa that are experiencing the imminent threats of emergent diseases, poaching and expanding human development. Increasing the quality of density estimates from field survey data will aid in the development of local conservation initiatives, national strategies and international policies on behalf of remaining ape populations. [source] Estimating deer abundance from line transect surveys of dung: sika deer in southern ScotlandJOURNAL OF APPLIED ECOLOGY, Issue 2 2001Fernanda F.C. Marques Summary 1Accurate and precise estimates of abundance are required for the development of management regimes for deer populations. In woodland areas, indirect dung count methods, such as the clearance plot and standing crop methods, are currently the preferred procedures to estimate deer abundance. The use of line transect methodology is likely to provide a cost-effective alternative to these methods. 2We outline a methodology based on line transect surveys of deer dung that can be used to obtain deer abundance estimates by geographical block and habitat type. Variance estimation procedures are also described. 3As an example, we applied the method to estimate sika deer Cervus nippon abundance in south Scotland. Estimates of deer defecation and length of time to dung decay were used to convert pellet group density to deer density by geographical block and habitat type. The results obtained agreed with knowledge from cull and sightings data, and the precision of the estimates was generally high. 4Relatively high sika deer densities observed in moorland areas up to 300 m from the forest edge indicated the need to encompass those areas in future surveys to avoid an underestimate of deer abundance in the region of interest. 5It is unlikely that a single method for estimating deer abundance will prove to be better under all circumstances. Direct comparisons between methods are required to evaluate thoroughly the relative merits of each of them. 6Line transect surveys of dung are becoming a widely used tool to aid management and conservation of a wide range of species. The survey methodology we outline is readily adaptable to other vertebrates that are amenable to dung survey methodology. [source] On the importance of estimating detection probabilities from at-sea surveys of flying seabirdsJOURNAL OF AVIAN BIOLOGY, Issue 6 2009Christophe Barbraud The primary and accepted method used to estimate seabird densities at sea from ships is the strip transect method, designed to correct for the effect of random directional bird movement relative to that of the ship. However, this method relies on the critical assumption that all of the birds within the survey strip are detected. We used the distance sampling method from line-transects to estimate detection probability of a number of species of flying seabirds, and to test whether distance from the ship and bird body size affected detectability. Detection probability decreased from 0.987 (SE=0.029) to 0.269 (SE=0.035) with increasing strip half-width from 100 to 1400,m. Detection probability also varied between size-groups of species with strip half-width. For all size-groups, this probability was close to 1 for strip half-width of 100,m, but was 0.869 (SE=0.115), 0.725 (SE=0.096) and 0.693 (SE=0.091) for strip half-width of 300,m, a typical strip width used in seabird surveys, for respectively large, medium and small size flying seabirds. For larger strip half-width, detection probability was higher for large sized species, intermediate for medium sized species and lower for smaller sized species. For strip half-width larger than 100,m we suggest that more attention should be paid to testing the assumption of perfect detectability, because abundance estimates may be underestimated when this assumption is violated. Finally, the effect of the speed of travel of flying seabird on the detection probability was estimated in a simulation study, which suggests that detection probability was underestimated with increasing flying speed. [source] Effect of count duration on abundance estimates of Black-capped VireosJOURNAL OF FIELD ORNITHOLOGY, Issue 1 2009David A. Cimprich ABSTRACT Distance sampling applied to point count surveys (point transects) has become a common method for estimating the absolute abundance of birds. When conducting point transects, detections of focal species are typically recorded during a fixed time interval. However, count duration has varied among studies and the effect of such variation on the resulting abundance estimates is unclear. My objective was to examine the effect of count duration on abundance estimates of male Black-capped Vireos (Vireo atricapilla). The abundance of these vireos in a 349-ha area in central Texas was estimated using 3-, 5-, and 6-min point transects and results were then compared to actual number present as determined by banding and territory mapping. The 3-min counts provided an estimate that was 26% greater than the actual number of male Vireos present (N= 201), but this number was within the corresponding 95% confidence interval (N= 157,413). Confidence intervals for the 5- and 6-min counts did not include the actual number of vireos present. The shortest count duration may have provided the most accurate abundance estimate because male Black-capped Vireos are typically active, sing intermittently, and sometimes move tens of meters between songs. Thus, shorter-duration counts may also yield the most accurate abundance estimates for other species that exhibit similar behavior. However, because behavior varies among species, I recommend that investigators collect preliminary data to establish an appropriate count duration when accurate estimates of absolute, rather than relative, abundance are important. RESUMEN El muestreo a distancia aplicado a conteos de punto (transectos de punto) se ha convertido en un método común para estimar la abundancia absoluta de aves. Cuando se conducen conteos de punto, la detección de especies focales, típicamente, se lleva a cabo durante un periodo de tiempo definido. Sin embargo, la duración de tiempo del conteo, varía en diferentes estudios y el efecto de dicha variación, en los estimados de abundancia, no está definido. Mi objetivo fue examinar el efecto del periodo de tiempo usado en los conteos utilizando como objeto de estudio a Vireo atricapilla. La abundancia de dichas aves en 349 ha en la parte central de Texas, fue estimada utilizando periodos de 3, 5 y 6 minutos en cada punto del transecto. Los resultados fueron comparados a números obtenidos con recobro de animales anillados y mapas de territorios. Los conteos de 3 minutos dieron como resultado un 26% más alto que el número de machos presentes en la localidad (N= 201). Pero dichos resultados estuvieron dentro del intérvalo de confiabilidad de 95% (N= 157,413). Intérvalos de 5 y 6 minutos no estimaron adecuadamente el número de vireos presentes. El conteo más corto (3 minutos) suministró los números más exactos, aparentemente porque el ave estudiada, típicamente está activa, canta de forma intermitente y en ocasiones se mueve de lugar (decenas de metros) entre canciones. Por lo tanto los conteos más cortos deben de proveer los estimados de abundancia más precisos para otras especies de aves con hábitos similares. Sin embargo, dado el caso de que la conducta entre especies varía, recomendamos a otros investigadores, que tomen datos preliminares para establecer la duración más apropiada de conteos, cuando se necesiten estimados de absoluta exactitud, en vez de estimados relativos de abundancia. [source] Effects of environmental variables on fish feeding ecology: implications for the performance of baited fishing gear and stock assessmentJOURNAL OF FISH BIOLOGY, Issue 6 2004A. W. Stoner The effectiveness of baited fishing gear ultimately depends upon behaviour of the target species , activity rhythms, feeding motivation, and sensory and locomotory abilities. While any environmental parameter that mediates feeding or locomotion can have an important influence on the active space presented by the bait and fish catchability, few biologists have considered how such variation in behaviour might affect catch per unit effort (CPUE) and the resultant stock abundance estimates or population parameters. This review reveals that environment-related variation in feeding behaviour can act through four different mechanisms: metabolic processes, sensory limitations, social interactions and direct impacts. Water temperature, light level, current velocity and ambient prey density are likely to have largest effects on fish catchability, potentially affecting variation in CPUE by a factor of ten. Feeding behaviour is also density-dependent, with both positive and negative effects. Over time and geographic space a target species can occupy wide ranges of environmental conditions, and in certain cases, spatial and temporal variation in feeding biology could have a larger impact on CPUE than patterns of abundance. Temperature, light and current can be measured with relative facility and corrections to stock assessment models are feasible. Making corrections for biological variables such as prey density and bait competitors will be more difficult because the measurements are often not practical and relationships to feeding catchability are more complex and poorly understood. There is a critical need for greater understanding of how environmental variables affect feeding-related performance of baited fishing gear. A combination of field observations and laboratory experiments will be necessary to parameterize stock assessment models that are improved to accommodate variation in fish behaviour. Otherwise, survey data could reveal more about variation in behaviour than abundance trends. [source] Life history and ecology of seahorses: implications for conservation and managementJOURNAL OF FISH BIOLOGY, Issue 1 2004S. J. Foster We present the first synthesis of the life history and ecology of seahorses, compare relationships for seahorses with other marine teleosts and identify research needs. Seahorses occurred primarily amidst temperate seagrasses and tropical coral reefs. Population densities were generally low, ranging from 0 to 0·51 individuals m,2, but reached 10 m,2 in some patches. Inferred life spans ranged from 1 to 5 years. Seahorses consumed live prey and possibly changed diet as they grew. Growth rates are poorly investigated to date. Reproduction and mating systems are the best-studied aspects of seahorse ecology. The relationship between size at first maturity and maximum size in seahorses conformed to that for other marine teleosts. All seahorse species were monogamous within a cycle, but some were polygamous across cycles. Direct transfer of clutches to the brood pouch of the male fish made it difficult to measure clutch size in live seahorses. After brooding, males released from c. 5 to 2000 young, depending on species and adult size. Newborn young measured from 2 to 20 mm in length, which was a narrower size range than the 17-fold difference that occurred in adult size. Newborn body size had no relationship to adult size. Both eggs and young were larger than expected among marine teleosts, even when considering only those with parental care, but brood size at release was lower than expected, perhaps because the young were more developed. The size of adults, eggs and young increased with increasing latitude, although brood size did not. Considerable research is needed to advance seahorse conservation and management, including (a) fisheries-dependent and fisheries-independent abundance estimates, (b) age- or stage-based natural and fishing mortalities, (c) growth rates and age at first maturity, and (d) intrinsic rates of increase and age- or size-specific reproductive output. Current data confirm that seahorses are likely to be vulnerable to high levels of exploitation. [source] Effects of sampling teams and estimation methods on the assessment of plant coverJOURNAL OF VEGETATION SCIENCE, Issue 6 2003Suzanne M. Kercher Abstract. We evaluated variability in cover estimation data obtained by (1) two sampling teams who double sampled plots and (2) one team that used two methods (line intercepts and visual estimation of cover classes) to characterize vegetation of herbaceous wetlands. Species richness and cover estimates were similar among teams and among methods, but one sampling team scored cover higher than the other. The line intercept technique yielded higher cover estimates but lower species richness estimates than the cover class method. Cluster analyses of plots revealed that 36% and 11% of plots sampled consecutively by two teams or using two methods, respectively, were similar enough in species composition and abundance to be paired together in the resulting clustering tree. Simplifying cover estimate data to presence/absence increased the similarity among both teams and methods at the plot scale. Teams were very similar in their overall characterization of sites when cover estimation data were used, as assessed by cluster analysis, but methods agreed best on their overall characterization of sites when only presence/absence data were considered. Differences in abundance estimates as well as pseudoturnover contribute to variability. For double sampled plots, pseudoturnover was 19.1%, but 57.7% of pseudo-turnover cases involved taxa with , 0.5% cover while only 3.4% involved taxa with > 8% cover. We suggest that vegetation scientists incorporate quality control, calibrate observers and publish their results. [source] Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian OceanMAMMAL REVIEW, Issue 2 2007T. A. BRANCH ABSTRACT 1Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303 239), sightings (4383 records of ,8058 whales), strandings (103), Discovery marks (2191) and recoveries (95), and acoustic recordings. 2Sighting surveys included 7 480 450 km of effort plus 14 676 days with unmeasured effort. Groups usually consisted of solitary whales (65.2%) or pairs (24.6%); larger feeding aggregations of unassociated individuals were only rarely observed. Sighting rates (groups per 1000 km from many platform types) varied by four orders of magnitude and were lowest in the waters of Brazil, South Africa, the eastern tropical Pacific, Antarctica and South Georgia; higher in the Subantarctic and Peru; and highest around Indonesia, Sri Lanka, Chile, southern Australia and south of Madagascar. 3Blue whales avoid the oligotrophic central gyres of the Indian, Pacific and Atlantic Oceans, but are more common where phytoplankton densities are high, and where there are dynamic oceanographic processes like upwelling and frontal meandering. 4Compared with historical catches, the Antarctic (,true') subspecies is exceedingly rare and usually concentrated closer to the summer pack ice. In summer they are found throughout the Antarctic; in winter they migrate to southern Africa (although recent sightings there are rare) and to other northerly locations (based on acoustics), although some overwinter in the Antarctic. 5Pygmy blue whales are found around the Indian Ocean and from southern Australia to New Zealand. At least four groupings are evident: northern Indian Ocean, from Madagascar to the Subantarctic, Indonesia to western and southern Australia, and from New Zealand northwards to the equator. Sighting rates are typically much higher than for Antarctic blue whales. 6South-east Pacific blue whales have a discrete distribution and high sighting rates compared with the Antarctic. Further work is needed to clarify their subspecific status given their distinctive genetics, acoustics and length frequencies. 7Antarctic blue whales numbered 1700 (95% Bayesian interval 860,2900) in 1996 (less than 1% of original levels), but are increasing at 7.3% per annum (95% Bayesian interval 1.4,11.6%). The status of other populations in the Southern Hemisphere and northern Indian Ocean is unknown because few abundance estimates are available, but higher recent sighting rates suggest that they are less depleted than Antarctic blue whales. [source] ABUNDANCE OF IRRAWADDY DOLPHINS (ORCAELLA BREVIROSTRIS) AND GANGES RIVER DOLPHINS (PLATANISTA GANGETICA GANGETICA) ESTIMATED USING CONCURRENT COUNTS MADE BY INDEPENDENT TEAMS IN WATERWAYS OF THE SUNDARBANS MANGROVE FOREST IN BANGLADESHMARINE MAMMAL SCIENCE, Issue 3 2006Brian D. Smith Abstract Independent observer teams made concurrent counts of Irrawaddy dolphins Orcaella brevirostris and Ganges River dolphins Platanista gangetica gangetica in mangrove channels of the Sundarbans Delta in Bangladesh. These counts were corrected for missed groups using mark-recapture models. For Irrawaddy dolphins, a stratified Lincoln-Petersen model, which incorporated group size and sighting conditions as covariates, and a Huggins conditional likelihood model, which averaged models that individually incorporated group size, sighting conditions, and channel width as covariates, generated abundance estimates of 397 individuals (CV = 10.2%) and 451 individuals (CV = 9.6%), respectively. For Ganges River dolphins, a stratified Lincoln-Petersen model, which incorporated group size as a covariate, and a Huggins conditional likelihood model, which averaged the same models described above, generated abundance estimates of 196 individuals (CV = 12.7%) and 225 individuals (CV = 12.6%), respectively. Although the estimates for both models were relatively close, the analytical advantages of the Huggins models probably outweigh those of the Lincoln-Petersen models. However, the latter should be considered appropriate when simplicity is a priority. This study found that waterways of the Sundarbans support significant numbers of Irrawaddy and Ganges River dolphins, especially compared to other areas where the species have been surveyed. [source] Density estimates of Panamanian owl monkeys (Aotus zonalis) in three habitat typesAMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2010Magdalena S. Svensson Abstract The resolution of the ambiguity surrounding the taxonomy of Aotus means data on newly classified species are urgently needed for conservation efforts. We conducted a study on the Panamanian owl monkey (Aotus zonalis) between May and July 2008 at three localities in Chagres National Park, located east of the Panama Canal, using the line transect method to quantify abundance and distribution. Vegetation surveys were also conducted to provide a baseline quantification of the three habitat types. We observed 33 individuals within 16 groups in two out of the three sites. Population density was highest in Campo Chagres with 19.7,individuals/km2 and intermediate densities of 14.3,individuals/km2 were observed at Cerro Azul. In la Llana A. zonalis was not found to be present. The presence of A. zonalis in Chagres National Park, albeit at seemingly low abundance, is encouraging. A longer-term study will be necessary to validate the further abundance estimates gained in this pilot study in order to make conservation policy decisions. Am. J. Primatol. 72:187,192, 2010. © 2009 Wiley-Liss, Inc. [source] Do trails affect relative abundance estimates of rainforest frogs and lizards?AUSTRAL ECOLOGY, Issue 6 2009RUDOLF Von MAY Abstract The selection of a sampling protocol is critical to study amphibian and reptile communities and in many instances researchers have combined the use of visual encounter surveys (VES) conducted on trails and off trails. The effect of human-made trails on relative abundance estimates of amphibians and reptiles has been assessed in a few temperate locations, but data are lacking for tropical sites. Our study was designed to address this issue by comparing abundance estimates of frogs and lizards on and off trails in a lowland rainforest in south-eastern Perú. We used nocturnal VES to sample frogs and lizards along transects established on trails and off trails in two different forest types. We found that the observed relative abundance estimates of frogs and lizards were affected by the location of transects (on trail vs. off trail) and the type of forest (floodplain forest vs. terra firme forest). We also found an interaction between the two main effects, indicating that the effect of transect location with respect to trails varies as a function of habitat. Observed frog abundances were higher on trails than off trails, indicating that studies that include VES on trails will bias relative abundance estimates in contrast to studies that include only VES off trails. We suggest that transects should be established only off trails, especially for monitoring studies because trail use by humans can have a strong influence on observed animal abundance. [source] | ||||||||||||||||||||||||||||