- Accidental entanglement in fishing nets is one of the leading threats to river dolphins in all of the river basins where humans and river dolphins overlap.
- Monitoring fisheries, their socio-economic value, the fishing methods applied, dolphin bycatch, and direct river dolphin catches, is critical to understanding the impact on dolphin populations and how to reduce fisheries-related deaths. Market surveys, interviews, and remote electronic monitoring can all yield valuable information.
- The creation of protected and managed areas, including time-area closures where fishing is temporarily prohibited to protect (seasonal) river dolphin habitats or prey, is a very effective way to keep harmful fishing gear away from dolphins, while having the added benefit of allowing fish stocks to recover in those reserves, contributing to sound ecosystem-based management.
- Gillnets are known to cause high rates of dolphin bycatch, and where possible should be replaced with more selective fishing gears like traps or poles and lines. Where this is not possible, technology like acoustic alarms (‘pingers’) or lights can be used to warn dolphins away from nets.
- Government-led, legally enforceable regulation is often needed to ensure effective implementation of conservation measures to reduce fisheries-related mortality. This requires surveillance and enforcement, which can be conducted by government authorities, trained park rangers, river guards and/or community members.
- Measures to reduce conflict between fisheries and dolphins are most effective if (fishing) communities have been involved in their development and implementation, and have clear roles to play. Training and support for alternative livelihoods, including ecotourism, aquaculture and the sale of local handicrafts and products, can provide an incentive to reduce fishing pressure while diversifying income sources.
How can fisheries impact river dolphins?
Fishing, and especially fishing with gillnets, is as serious a threat to river dolphins as it is to aquatic mammals globally1, 2. Fisheries bycatch was one of the primary causes of the baiji’s extinction3, 4 and is currently recognised as a threat to virtually all river dolphins57. In Pakistan, the deaths of 51 Indus dolphins have been attributed to net entanglement since 2008 in a 190km stretch of river (unpublished data, WWF Pakistan). In the Mekong River in Cambodia, at least 153 dolphins died from gillnet entanglement between 2002 and June 2018 (unpublished data, WWF Cambodia), while 67% of dolphin deaths with a known cause between 1995 and 2018 (99 animals) in Indonesia’s Mahakam River were attributed to gillnet entanglement (database YK RASI: Danielle Kreb). Considering the last two populations are below 100 individuals each, gillnet fishing clearly poses a significant threat to their survival.
Understanding the relationship between fishers and river dolphins is necessary to change this situation. Interview-based methods are the most common means of gathering information. In many river basins, dolphins are perceived by fishers to be competition for fish resources8. This can lead to conflict, including the deliberate killing of the dolphins as has been documented in the Amazon9, 10. In some countries, river dolphins’ oil and flesh are used as bait in targeted fisheries. For example, the Piracatinga (a carnivorous catfish) fishery in the Amazon is thought to be a major driver of decline for some populations of Amazon river dolphins7, 11.
Illegal activities, such as fishing with explosives and electrofishing are widespread in many rivers, including the Ayeyarwady, Indus, Mekong, Mahakam and Yangtze3, 12 Over-exploitation of fish and other organisms, and the resulting depletion of prey populations, have long been recognised as an indirect threat to marine mammals13, although this is difficult to prove in the case of river dolphins.
How can we reduce the impact of fisheries on river dolphins?
To reduce fisheries bycatch or other fisheries conflicts, a number of methods are available, including:
- Bycatch monitoring: Analyses and modelling to understand the fisheries, gears, communities, and socio-economic drivers involved in bycatch can be achieved through market surveys, interviews in fishing communities, or a community-based approach where fishers are enlisted to help collect data on accidental bycatch. This worked well in the Peruvian Amazon to generate bycatch estimates14 In the small scale artisanal fisheries that are typical in many river dolphin habitats, remote electronic monitoring (REM) using rugged, solar powered cameras positioned on vessels to video or photograph fishing practices and potential bycatch can be an effective means of collecting data15, 16.
- Protected areas and spatial/temporal closures can be used to prevent fisheries in river dolphin habitats that are important for feeding or breeding, or at times of year when dolphins may be more vulnerable to bycatch.
- Gear modifications that can reduce cetacean bycatch include weakened nets that are designed to allow cetaceans to break free from entanglement, exclusion devices that prevent cetacean interaction with gear or provide them with escape exits, and nets that incorporate materials that are more reflective to cetacean echolocation. Scientific assessments of most gear modifications have, to date, demonstrated limited effectiveness17. However, many modifications have not yet been rigorously tested and there are several new emerging technologies. Additional technologies that help dolphins detect nets and/or to warn dolphins away include the use of acoustic alarms (‘pingers’)18 or lights19.
- Alternative gears that are more selective than gillnets can be helpful. These include pole and line fishing, traps, and nets with smaller mesh size that are less likely to hook onto dolphin beaks or flippers20.
- Bans on using dolphins as bait or trade in target fish: Where dolphin oil or meat is used as bait in fisheries, governments can either impose bans on the practice, or impose bans on the trade in the carnivorous fish species that are fished with dolphin bait. This has had some success in the Amazon7, but required rigorous enforcement.
- Alternative livelihoods: In many riverine communities, fisheries are seen as the only reliable source of income and food. Initiatives that provide alternative employment or that support community members to develop new skills can help reduce fishing pressure. Examples of alternative livelihoods include ecotourism (fishers who know rivers well can make very good guides, and families can provide homestays, meals, etc), sale of traditional handicrafts, work as rangers/river-guards, or farming. In an innovative programme in Colombia, villagers use catfish that have been partially eaten or ‘damaged’ by dolphins to make fish patties or burgers.
- Shift to aquaculture: A shift from non-selective fishing methods like gillnets to carefully planned aquaculture can reduce the risk of bycatch, while diversifying sources of income for riverine communities. However, it’s critical to ensure quality methods are implemented as poor aquaculture practices can result in disease outbreaks, the introduction of invasive species, water contamination, and the depletion of wild fish stocks for feed production21.
The tools and strategies above have all proven to reduce fisheries-related mortalities in river dolphin populations. However, there is often a big gap between the success of limited trials or studies, and effective implementation of strategies that can reduce bycatch on a wider scale. While education and awareness-raising can help fishers and communities learn about river dolphin threats and conservation measures, a system of (legally enforceable) incentives is often required to ensure lasting compliance with good practice on a broad scale.
- Legally enforceable regulations: Government regulations can focus on the protection of dolphins (e.g. granting protected species status, with fines or penalties for hunting or harassing animals), or on fishing practices. For example, regulations can be implemented to reduce or eliminate the use of fishing gears/methods known to pose the highest risk of bycatch, or make some of the other practices that are recommended above mandatory (time area closures, alternative gears, use of ‘pingers’ or lights). With surveillance and enforcement, this can help cetacean populations recover. For example, harbour porpoise populations off the California coast had declined due to mortality from bycatch in the region’s gillnet fisheries, but were seen to recover once gillnets were banned in their primary habitat22. This strategy is being applied by the Chinese government to help boost the critically endangered Yangtze finless porpoise population.
- Effective surveillance and enforcement: Laws and regulations are only effective if they can be enforced, and protected areas are only protected if they are regularly patrolled and monitored. Where traditional law enforcement bodies (police, fishing authorities) may not be available to conduct regular patrols, community members or park rangers can be trained to step in. The Spatial Monitoring and Reporting Tool (SMART) is a system that is successfully used by park rangers around the world to monitor wildlife and biodiversity while they are conducting surveillance and enforcement. It is used, for example, by river guards working to protect Irrawaddy dolphins in the Mekong River in Cambodia23, 24.
- Ecosystem-based fisheries management: Effective fisheries management is often based on science that allows managers to calculate the maximum sustainable yield of a fisheries stock; the amount of fish that can be harvested without driving down population numbers and the number of mortalities that a population can sustain without leading to declines. This is embedded in an ecosystem-based management approach to fisheries25, and has been recommended for the management of small-scale artisanal fisheries in the Amazon River Basin26.
- Community-based management: Implementation of, and compliance with, conservation measures will be more effective if there is buy-in from the involved communities and they have a clear role to play in ensuring the long-term success of those measures27, 28. In some cases, this has even led to the recovery of commercially important freshwater fish populations29. Riverine communities can play an important role in fisheries management by, for example, contributing their local ecological knowledge to localised management plans and being engaged as river-guards to monitor and enforce regulations. See the Community Engagement page of this website to learn more.
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- Iriarte, V. & Marmontel, M. Insights on the use of dolphins (boto,Inia geoffrensis and tucuxi, Sotalia fluviatilis) for bait in piracatinga (Calophysus macropterus) fishery in the western Brazilian Amazon. Journal of Cetacean Research and Management, 163-173 (2013).
- Loch, C., Marmontel, M. & Simões-Lopes, P., C. Conflicts with fisheries and intentional killing of freshwater dolphins (Cetacea: Odontoceti) in the Western Brazilian Amazon. Biodiversity Conservation 18, 3979-3988 (2009).
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- Dawson, S. M., Northridge, S., Waples, D. & Read, A. J. To ping or not to ping: the use of active acoustic devices in mitigating interactions between small cetaceans and gillnet fisheries. Endangered Species Research 19, 201-221, doi:10.3354/esr00464 (2013).
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- Forney, K. A., Moore, J. E., Barlow, J., Carretta, J. V. & Benson, S. R. A multidecadal Bayesian trend analysis of harbor porpoise (Phocoena phocoena) populations off California relative to past fishery bycatch. Marine Mammal Science n/a, doi:https://doi.org/10.1111/mms.12764 (2020).
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