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Hydro-acoustic Survey of Deep Plools in the Mekong River

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Hydro-acoustic Survey of Deep Plools in the Mekong River

Author: Mekong River Commission
USD 5.00

Book's Description

Deep pools in the mainstream of Mekong are important habitats in the life cycle of many commercially important fish. In addition to supporting a sedentary fauna of their own, the pools offer a dry season refuge for many of the migratory species that provide the recruitment for the large-scale fisheries further downstream. Despite their commercial importance, little detail is known of the ecology and biology of these habitats and the fauna they support. Much of what is known comes from interviews with local fishers and surveys of their catches. These provide a lot of information about the type and number of fish living in the pools, but little data on the distribution of fish in the pools, especially data on the micro-habitats preferred by many fish.

Hydro-acoustic surveys, which work on the same principles as sonar, provide a means of acquiring spacial data to complement the information gathered from fishers. It is a relatively untried technique in tropical rivers such as the Mekong . However, a pilot survey conducted in the Siphandone area of southern Lao PDR during early 2003 demonstrated the method worked well in pools greater than 10 m deep and in conditions of laminar flow.

This paper documents the results of a follow-up survey conducted by IFReDI (Inland Fisheries Research and Development Institute, Phnom Penh ), LARReC (Living Aquatic Resources Research Centre, Vientiane ) and the University of Bergen, Norway, in late 2003 and early 2004. The survey, which was planned and located based on information provided by local fishers, acquired hydro-acoustic data from 69 deep pools located in the Mekong River in Stung Treng province, northern Cambodia and Champassack province, southern Lao PDR. During the same period, catch per unit effort (CPUE) surveys were conducted with Lao fishers who target deep pools.

Echograms produced from the hydro-acoustic data clearly showed fish and shoals of fish both in the ,o p en water and congregating near topographic features such as crevices and steep banks in the riverbed. Statistical aggregation of data from all the pools was used to map biomass and fish density. This e ealed that fishes showed preference for particular water depths. In general, both biomass and fish density increase until a depth of about 30 m below which these measures fall-off reaching a minimum at around 50 to 60 m. At greater depths, both biomass and fish density increase once more and there is some evidence of larger fish (greater than 1-2 m) living in the deepest pools. The data also showed that bile biomass was greater during the wet season, fish density was lower, suggesting more larger fish live in the pools during these times. Other observations, such as the greater biomass and fish density in ambodian pools than in the pools in Lao PDR, remain unexplained, but probably relate to the preference particular species (or communities of fishes) for particular micro-habitats within individual deep pools.

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