Background
After an intensive six week search by a team of international scientists, the Yangtze River dolphin was declared functionally extinct on January 3, 2007. Despite months of effort, the lack of sightings of the species led the researchers to conclude that although it was possible that a small number of individuals persist, the population can never recover. This represents the first recorded extinction of a cetacean species, but conservation biologists fear that other species face similar threats and may suffer a similar fate. The Gangetic Dolphin faces similar threats to those which devastated the Chinese species, and in the absence of a high level of effort is at risk of imminent extinction.
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Discussion Questions
1. In order to categorize a species as endangered or threatened much needs to be known about the natural history of the populations. This information must be evaluated in light of the environmental conditions that occur throughout the range of the species and the factors that render the species most vulnerable to extinction. Is the current status of the species predictable based on these factors?
Response
2. The audio clip describes efforts to protect the species in the Vikramshila Dolphin Sanctuary. Looking at the information at the Whale and Dolphin Conservation Society (www.wdcs.org), discuss the probability of the sanctuary protecting the dolphin in light of the threats to the species and practices that have proven effective for other species.
Response
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Responses
Question 1.
This type of analysis is an important part of understanding endangered species, requiring the student to focus on two key components: characteristics of the species that create vulnerability to extinction and factors in the environment that threaten biodiversity. The lists below are not comprehensive, but provide a basis for beginning the analysis; note that these can be used to assess any species or population.
Characteristics of Endangered Species
- Initial rarity - With only 2000 left broken into several populations the Gangetic Dolphin is rare. Certain populations are already vulnerable to inbreeding and stochastic extinction.
- Large area requirements - While there is little detailed information available about the species, a large aquatic predator like this certainly requires a large area for foraging.
- Specialized habitat requirements - The preference of the species for areas at the confluence of rivers and the requirement for deep waters can be considered specialized habitat requirements for a river species.
- Higher trophic level species - As a large predator the dolphin would be considered a high trophic level species. This also increases the vulnerability to the bioaccumulation of toxins in the tissues of the species.
- Local Endemics - Although the species does occur in different areas (IUCN, 2005: http://www.redlist.org/search/details.php?species=41758), the restricted distribution of the species significantly increases the probability of extinction.
- Migratory species - The species travels the length of the river in a regular migration.
- Species with poor dispersal abilities - Limited by the salinity of the waters, species are probably restricted to the rivers in which they are born.
- Colonial nesting species - Does not apply.
- Economic value - The blubber of the species is economically valuable, and there is evidence that the species is used as a food source.
- Perceived threat to humans and livestock - Does not apply
- Long lived species/low reproductive rate - Again, natural history information requires additional research but with a predicted maximum longevity of 30 years, and an age of sexual maturity between six and ten year, an expected slow reproductive rate increases the vulnerability of the species to extinction.
- Other factors: - The use of sonar in foraging makes the species vulnerable to changes in noise conditions in the habitat area.
Threats to Biodiversity
- Collection (including hunting, trapping or poaching) - Although there is evidence to suggest that education and regulations are reducing the harvesting of the species, poaching continues.
- Habitat destruction or degradation - Increased siltation reduces the areas of deep water necessary for the species.
- Habitat fragmentation - The barrages and dams along Ganga and her tributaries fragment the habitat, preventing migration and isolating smaller populations of dolphins.
- Introduction of invasive species - Not a known issue for the species
- Pollution - Ongoing pollution is changing the ecology of the river and threatens the prey base. The introduction of heavy metals and organic toxins to the river has a high probability of harming the populations.
Indirect Effects
- Changes to the environment may disrupt species interactions and the autecology of the species.
- Increased boat noise may affect the success of the species foraging.
Thus the characteristics of the species considered in light of the threats extant in the environment suggest that the current endangered status of the species is predictable.
Question 2:
Possible Response: In-Situ conservation efforts which protect the species in their own habitats are preferred over ex-situ strategies, which rely on zoos, aquaria or botanical gardens to preserve biodiversity in an artificially controlled environment. An evaluation of the feasibility of using in-situ strategies requires the following questions be answered:
Is an adequate habitat area available to protect a viable population of the species, and if not is there adequate supporting habitat in the area that is likely to persist despite the lack of formal protection?
More research is probably needed to determine the size of the population than can be supported within the 60 km2 area. The 50/500 rule, which states that at least 500 breeding individuals are needed in a population to prevent the loss of genetic viability and 50 as an absolute minimum population, suggests that the small area is of concern.
Is there sufficient connectivity between the conservation area and other suitable habitats to allow for adequate gene flow to prevent inbreeding and serve as a source of colonists should a population go extinct?
The Farakka barrage creates an impenetrable barrier to dolphin movement isolating this population and increasing the probability of extinction.
Can the threats to the species be controlled within the conservation area?
Inadequate enforcement funds suggest that poaching within the sanctuary is possible. Pollutant accumulation and habitat degradation associated with siltation are also likely to continue in the sanctuary. Without additional funding, there is concern about the effectiveness of the preserve. While clearly an important step in the preservation of the species, additional efforts will almost certainly be needed to protect the species in Ganga.
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