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Blog, Lao PDR

eDNA Sampling

It’s surprisingly difficult to find some of the world’s biggest fish. Despite their behemoth size, many of the largest freshwater fish species are critically endangered, meaning there are few of them left to find. Such is the case of the Mekong Giant Catfish (Pangasianodon gigas), the world’s largest freshwater fish, which can grow up to nearly 10 feet long and weigh 650 pounds. Trying to track down this elusive giant in an expansive setting like the Mekong River Basin is a daunting task, coupled with the fact that many traditional fish sampling methods, such as using nets or electrofishing, could injure or kill these rare fish. That’s where environmental DNA (eDNA) techniques can come to the rescue. Methods using eDNA can detect trace amounts of genetic material that a fish or other animal leaves behind in the river, whether from skin cells, mucus, urine, or other sources. A team of researchers from the French laboratory SPYGEN, Griffith University in Australia, and the World Wide Fund for Nature (WWF) in Laos has successfully demonstrated the use of eDNA for detecting giant catfish in the vast Mekong River (Bellemain 2016). These findings suggest new approaches for the study and conservation of rare aquatic species.

There are many benefits and challenges to using eDNA in freshwater ecosystems. Studying eDNA from water samples is a non-destructive way to sample for many species at once, including very rare species. However, DNA breaks down rapidly in the environment, leaving a short window of opportunity to detect it, and such studies can’t confirm if the species is alive or dead. Still, the approach holds appeal for settings where finding a rare fish is like searching for a needle in a hay stack. To test for eDNA, water samples are collected, filtered, and probed with special genetic tools called primers that latch on to and amplify DNA from a particular species of interest. The study of giant catfish in the Mekong is the first to apply eDNA tools to detect a single species of interest in a large and diverse tropical river that is filled with hundreds of other fish species.

Mekong Catfish Sign

The team validated the eDNA technique at a reservoir in Thailand that serves as a hatchery for Mekong giant catfish. Successfully detecting Mekong giant catfish DNA in water where the fish were definitely present helped confirm the tool was sensitive to this species. The team then set out to collect water samples to search for giant catfish along the Lower Mekong River, traveling to six locations in Laos, Thailand, and Cambodia. They chose their sampling locations based on historical catch records of Mekong giant catfish, as well as the ecological knowledge of local fishermen. Mekong giant catfish are known to seek refuge in deep pools in the river during the dry season when the water level is lower. The scientists therefore collected water samples at deep pools during the end of the dry season (April and May). Using a tool called an immersion cylinder that can collect water from specific depths, they sampled at the bottom of the river, in the middle of the water column, and at the water’s surface at each site.

After analyzing their samples in the laboratory, the team documented a single positive detection of giant catfish DNA at one site, on the border between northern Thailand and Laos, in an area that local people believe the fish uses for spawning. The scientists conclude that the scant results highlight the rarity of the species, and the multiple conditions that must be met to obtain a positive eDNA detection. The study authors write that eDNA is a useful tool for conducting baseline biodiversity surveys in rivers, and for identifying key locations that can be more intensively sampled with other methods, or designated as protected areas. The many threats to the survival of the giant catfish underscore the need for innovative approaches to conservation in the Mekong basin, such as this one.

Blog, Lao PDR, Mekong Fish Network News

Closing Workshop in Ban Sa KaiFresh roasted fish and sticky rice accompanied conversations about fish populations and community fisheries management at a lunch celebrating the close of the Mekong Fish Network’s first participatory fisher survey program in Lao PDR. FISHBIO conducted this pilot study with a grant from the Mohamed bin Zayed Species Conservation Fund, and facilitation help from the Sang Thong District Agriculture and Forestry Office. For three months, fishermen from the villages of Ang Noi and Sakai worked with FISHBIO staff to record important data related to their fish catch. The pilot project aims to create a standardized data sheet that can be used as a common data collection method throughout the Mekong River Basin. This data collection has to strike a balance between thoroughness and simplicity to be useful to both scientists and fishers.

An overarching goal of the project is to train community members to become more informed resource users and managers. The fishers of Ang Noi and Sakai participated in training workshops where they learned how to record standard fish lengths, use digital scales, and better identify the fish they were catching. They also learned to record data on fishing gear types, habitats fished, and the amount of time spent fishing. Members of each village’s Lao Women’s Union collected and organized the project data sheets, and were also responsible for photographing any rare or unknown fish.

Closing Workshop lunchThe preliminary data from this project give an interesting look at the local fish population as well as local fishing techniques. Fishers caught more than 62 different species in the three-month period, including two species of conservation interest, Probarbus jullieni and Probarbus labeamajor (both classified by the IUCN Red List as endangered species). A total of 22 Probarbus fishes were reported in the catch, and 86% came from Ang Noi. While both villages fish in waters known to be Probarbus spawning habitat, Ang Noi fishermen use nets more frequently than the fishers of Sakai, who use longlines far more frequently. Identifying which gear types are more hazardous to endangered fishes is just one way information from the standard sampling program will be useful to resource managers.

The close of the first pilot study was celebrated as a success by all participants and collaborating organizations, and has inspired the two villages to begin planning Fish Conservation Zones for Probarbus. FISHBIO hopes to continue our work with these communities to continue monitoring activities and support the development of conservation strategies and capacity building for both the villagers and district government.

Blog, Events, Lao PDR

Some workshop attendeesScientific research can inform the best designs and strategies to help fish move past migration barriers, such as dams, weirs, and road crossings. That was the take-home message of the Lao National Workshop on Fish Passage recently held in Vientiane, Lao People’s Democratic Republic. Experts from Lao PDR, Australia, Brazil, France, and the United States shared experiences addressing fish passage in their respective countries. Speakers stressed that fish passageways in Lao PDR need to be designed specifically for the native species of the region, which may require different approaches than those that have worked elsewhere. A particular challenge to fish passage design in a region with as much biodiversity as the Mekong is accommodating the wide variation in sizes and swimming abilities of fish species that range from 3 cm to 3 m in length.

The conference focused primarily on floodplain barriers, which block fish from moving laterally off the main river into the tributaries and wetlands of the watershed. The first day of the workshop focused on helping fish traveling upstream, which may be breeding adults trying to migrate to their spawning grounds, or juveniles accessing nursery habitat. Researchers presented methods for prioritizing existing structures that need modification for fish passage — a necessary exercise, since they identified nearly 2,500 potential barriers in a single river catchment (Xe Chamopone). Such barriers can be roads, irrigation structures, or natural obstructions like logs. Scientists also described an experiment to test various fish passage designs at a floodplain regulator in the Pak Peung wetland of Central Lao PDR (Baumgartner 2012). Unlike salmon, which can leap over barriers 2 m high, Mekong fish in the 3-60 cm size range could generally clear a step that is 10 cm tall (4 in), the researchers found during laboratory studies. Based on these findings, they constructed a fishway with 43 sequential 10-cm steps, which stretched 150 m (492 ft) in length. Because fish passageways can’t be too steep, the taller a barrier is, the longer a fishway needs to be to clear it, and hence the more expensive it is to construct and maintain.

The second day of the conference focused on creating passage for downstream migrating fish, which can be either adults or juveniles travelling from floodplains to the mainstem river. Several researchers discussed the potentially hazardous hydraulic conditions fish may encounter when passing through structures, including pressure changes, shear between two shifting masses of water, and collision with hard surfaces. Researchers indicated that structures requiring water and fish to pass underneath a barrier (such as a sluice gate) proved more damaging to fish than those allowing fish to pass over the top of a structure (such as a fixed crest weir). Scientists also used a pressure chamber to demonstrate the barotrauma, or physical injury from changes in pressure, that fish experience when passing through turbines and weirs: as the pressure drops, the gasses inside a fish expand. Participants discussed plans to build fish swimming and testing facilities at the National University of Laos so more fish passage experiments can be conducted on a greater variety of local species. The workshop highlighted many successes in helping fish move across floodplain barriers, which are generally 6 m (20 ft.) or shorter. A number of additional factors will need to be considered when designing and evaluating fish passage at larger barriers.

Blog, Fishing, Lao PDR, Project Spotlight

Paticpatory research

Fish live in water where they are difficult to see, catch, and assess their health and abundance. That typically means research projects are labor intensive and expensive. As is evident in this picture, many people can be involved in fisheries field research. In this case, FISHBIO trained local villagers in Lao PDR to collect fish abundance and harvest data, which serves several purposes. First, hiring local staff at local prevailing wages keeps the overall cost of the research project reasonable. Second, and more importantly, this research provides jobs to local people in a region where finding work can be difficult. Perhaps most importantly, projects such as this one increases local residents’ understanding of their fishery resources and hopefully leads to better conservation efforts.

This outdoor classroom provided a nice setting for a week-long crash course in species identification. In this region of the Mekong River, it is believed there are around 100 fish species, of which only about 60 have been described in scientific literature. In addition to providing opportunities to discover new species, it also poses challenges with data collection and scientific accuracy. Upon graduating from their week-long classroom training, these new fish technicians began another week of intensive field training, after which they completed an 18-month-long effort to assess their local fishery and harvest practices.