Freshwater Dolphins and Porpoises
Freshwater cetaceans include some of the world’s most highly adapted and threatened mammals. One of them, the Yangtze River dolphin, became extinct early in this century. Four of the six currently recognized cetacean species with freshwater populations occur in Asia, and the other two species (with several subspecies) are found in the Amazon and Orinoco River basins of South America. All of these populations, except the Tucuxi (Sotalia fluviatilis) in South America are endangered or critically endangered according to the International Union for Conservation of Nature (IUCN) Red List.
Freshwater cetaceans (including five dolphin species and a porpoise) have declined dramatically in numbers and range, especially in Asia. The Yangtze River dolphin (Lipotes vexillifer) was finally driven to extinction in the last two decades. The threats to freshwater cetaceans are diverse, longstanding, and difficult to assess and manage. Bycatch in fishing gear (entanglement or entrapment, usually leading to death) is the most serious and immediate problem for most populations, and gillnets are the greatest currently recognized cause of human-induced mortality. Freshwater cetaceans are also vulnerable to habitat modification and degradation (e.g., noise, chemical pollution, dams, lack of stream volume), and they compete with humans for prey. Vessel strikes, under-water explosions, the shock from electro-fishing, and entrapment in water management structures, notably irrigation canals, can cause injury or death. Some of these factors kill animals outright, and others impair their health or undermine their reproductive capabilities and social behavior. Unlike marine cetaceans, many freshwater animals live in environments where the very availability of water can be in doubt.
All freshwater cetaceans require adequate water flow and water quality within their range as basic elements of suitable habitat to support their physical health, mobility, and ability to forage efficiently and find prey. In freshwater (and estuarine) ecosystems, more so than in coastal or oceanic systems, such basic elements are finite and may be completely regulated, modified, or destroyed by human activities. The constricted nature of riverine habitat, and the inescapable need to share that habitat with humans, increases the vulnerability of these animals to bycatch in fisheries, overfishing of their prey, disturbance by noise, and being struck or displaced by vessels. In Brazil, Amazon River dolphins (Inia geoffrensis), or botos, and tucuxis (Sotalia fluviatilis) are killed and used for bait in a fishery for a catfish, the piracatinga. Although most of the identified threats to freshwater cetaceans are widespread, and most freshwater cetacean populations face multiple threats, the types and intensity of human activities differ between different rivers. Nonetheless, in all cases, the human impact on river systems and on freshwater cetaceans is significant.
What the Commission Is Doing
The Marine Mammal Commission supports both targeted efforts to address the conservation of specific populations and regional efforts to strengthen freshwater cetacean conservation. Also, through its regular participation in the work of the International Whaling Commission Scientific Committee’s Sub-committee on Small Cetaceans, the Marine Mammal Commission seeks to make sure these “non-marine” marine mammals are given due consideration in accordance with their exceptional vulnerability.
In October 2009, the Commission co-sponsored a workshop in Samarinda, Indonesia, on Establishing Protected Areas for Asian Freshwater Cetaceans in Asia.
The Commission also participated in the Third Southeast Asian Marine Mammal Symposium (SEAMAM III) in Langkawi, Malaysia, from March 4-10, 2013. SEAMAM III considered issues related to the conservation and biology of coastal/inshore, estuarine and riverine marine mammals in Southeast Asia.
Additionally, the Commission provided expertise to a meeting to draft an Indus River Dolphin (Platanista gangetica minor) Conservation Strategy and Action Plan, 2012 – 2022, held by WWF-Pakistan in Lahore, Pakistan, April 3-4, 2012. The Commission provided grant support to Gill Braulik for research on distribution, abundance, habitat use, and taxonomy crucial to understanding the conservation needs of the Indus River dolphin.
The Irrawaddy dolphin (Orcaella brevirostris) population in the Mekong River has been reduced to fewer than 100 individuals, primarily due to entanglement in fishing nets. The Commission has supported WWF-Cambodia and the government of Cambodia in bringing experts on marine mammal health, demography, and behaviour to the country to assist them in assessing the threats to this population and developing conservation strategies and on-the-ground capability in the areas of science, law enforcement and health assessment. At the most recent workshop, in January 2017, the Cambodian fisheries agency reported on progress in removing gillnets from the core zone of the Mekong River dolphins. This was overshadowed by news of the proposed construction of the Sambor and Stung Treng hydropower dams. If built, these dams will eliminate or transform most of the dolphins’ remaining riverine habitat.
On December 9, 2014, an oil tanker collision spilled 350,000 liters of furnace oil into the waterways of the world’s largest mangrove forest in the Sundarbans, Bangladesh. This spill had the potential to impact the freshwater Ganges River dolphins (Platanista gangetica gangetica), as well Irrawaddy dolphins and finless porpoises (Neophocaena asiaeorientalis). In support of a joint United Nations/Government of Bangladesh Sundarbans oil spill response mission, the Commission funded Brian Smith and the Sundarbans biologists from the Wildlife Conservation Society to provide their expertise on the marine and freshwater cetacean species of the area and assist in the management of the spill and assessment of its impacts.
Commission representatives participating in the Scientific Committee of the International Whaling Commission have worked in the Sub-Committee on Small Cetaceans to draw attention to the impact of the use of meat from the two Amazonian freshwater cetacean species, the boto (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis), for bait in the piracatinga catfish fishery. The government of Brazil responded to the recommendations of the Scientific Committee by placing a five-year ban on fishing for and marketing piracatinga in January 2015. Nevertheless there is strong evidence that the practice of using dolphins for bait continues and that much greater attention to this issue, and to other problems facing South American freshwater dolphins, is warranted.
Commission Reports and Publications
|Letter Date||Letter Description|
|April 26, 2016|
|March 31, 2014||
See also: Ambassador’s_response_letter
Bycatch in fishing gear, especially gillnets, is the most serious and immediate problem for most populations. Freshwater cetaceans are also vulnerable to habitat modification and degradation (e.g., noise, chemical pollution, dams, lack of stream volume), and they compete with humans for prey. Vessel strikes, fishing with explosives, and entrapment in water management structures, notably irrigation canals, can cause injury or death.
Current Conservation Efforts
The Commission continues its engagement on freshwater cetaceans both within the IWC Scientific Committee and through interactions with field researchers and conservationists in Asia and South America.
The Future/Next Steps
The threats to freshwater cetaceans are ongoing and the impacts of human development need to be managed. The Commission is encouraging further work on Irrawaddy dolphin conservation and behavior in the Mekong as enforcement efforts are strengthened there and is working to build support for efforts to understand and address threats to Irrawaddy dolphins in Myanmar and Indonesia. The IWC Scientific Committee recently highlighted the dire situation of the Yangtze finless porpoise which, without additional conservation efforts by the Chinese government, may follow the baiji to extinction in this heavily industrialized, densely populated river system.