Abstract
Assessment of population trend and risk of extinction, essential for informed conservation, needs baselines including percentage of population decline, extent of occurrence, population size, population structure and probabilities of extinction. Construction of these baselines usually claims long-term census efforts that are often insufficient or even lacking for many cetaceans, especially for those nearby rapidly developing countries. Restricted to variation from current census techniques, however, the approach based on long-term census database is unlikely to detect early or recent sign of population decline. Here, I propose an integrative perspective, the systematic demographic analysis, to solve life history and demographic parameters essential for status and risk assessment for the cetacean populations. Transect technique with the aid of GPS records and environmental characteristics can be used to estimate population abundance and figure the extent of occurrence and critical habitat, information essential for sound habitat protection. Capturemark- recapture technique based on the database from individual photo-ID histories can be used to estimate population size, apparent survival rate and life history parameters. Collections of stranded and by caught carcasses can be used to solve life history parameters, age-specific survivorships or mortality rates and population genetic diversity indirectly relating to population size. Applications of population viability analysis to above parameters such as VORTEX model or other individual-based stage/age matrix model that factors the stochasticity and uncertainty can be used to solve the likely range of rate of decline and extinction risk of threatened population. Finally, I emphasize the need to integrate the histories of long-term land use and landscape change when formulating habitat management programme for the rare and/or endangered populations to avoid skipping the low-sighting habitat from intense anthropogenic impacts.
Highlights
The precautionary principle of conservation calls necessary actions to prevent or mitigate any threat that is possible to endanger the long-term survival of a population, even if the interaction between threats and population survival has not yet been clearly elucidated
When dealing with conservation of rare or threatened species/populations, policy makers, stakeholders and scientists frequently ask: What is current status of the species/population concerned? How fast is the current population decline? What is the chance the endangered species or population becomes extinct in future? How many years do we still have to reverse population decline? Answers to these questions lead to the assessment of population status and extinction risk
The population trend can be estimated by the long-term census database; the applicability of census approach in estimating population trend is restricted by the variation (CV) from currently-used census techniques
Summary
The precautionary principle of conservation calls necessary actions to prevent or mitigate any threat that is possible to endanger the long-term survival of a population, even if the interaction between threats and population survival has not yet been clearly elucidated. The baselines for status and risk assessment of the threatened populations/species can be approached by several techniques in cetaceans, from long-term and periodical census monitoring [7] to meta-analysis of stranded and/or by caught carcass collections [8,9]. Based on survival-reproduction modeling demographic approach provides an indirect way to estimate population trend and, forecast the risk of extinction, including the probabilities (PE) and date (TE) of extinction, under assumed scenarios for threatened species/populations [7,8,9,26].
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