Conservation Actions
Research into population trends and threats to the species and its habitats is needed. Catch, trade and transportation is forbidden in Laos (Kottelat and Whitten 1996) where it is a Schedule II species (I. Baird pers. comm. 2011), and is also listed in the Red Data Book for Viet Nam (Baird 2006). International trade is banned (CITES Annex I, since 1975).The Cambodian government is regulating the use of large mesh gill nets in northeastern Cambodia. The species reportedly benefited from freshwater conservation zones established in southern Lao PDR during the 1990’s (Baird 2006), but some of these zones may no longer exist. The species would benefit from fishing regulations to control over-harvesting and protected areas to safeguard spawning sites.
Location Information
Historically recorded from the Mekong in Thailand, Viet Nam, Cambodia and Lao PDR (to at least northern Laos), and from Malaysia (the Pahang, Terengganu, and Perak basins). In Thailand, it is known from the Chao Phraya and Mae Klong basins.In the Pahang River Basin of Malaysia, the species is extremely rare, and populations have dropped significantly in the Perak River Basin due to hydropower development and subsequent changes in stream hydrology (Baird 2006). Roberts (1992) and Baird (2006) state that the Mekong River supports the last relatively healthy population of the species. As recently as 1989 it was reported as “extremely abundant” in the Mekong, but subsequent accounts indicate a significant drop in abundance since (Roberts and Warren 1994, Roberts and Baird 1995, Singhanouvong et al. 1996). Populations in many locations in Lao PDR appear to have declined significantly (Baird 2006).
Geographic Range
Extant
Cambodia, Lao People's Democratic Republic, Malaysia, Thailand, Viet Nam
Population Information
In the Mekong, this important fisheries species is under serious long-term decline and this decline, evidently, is basin-wide. The most obvious (but not necessarily only) reason is over-fishing with gillnets during the reproductive migrations and spawning periods (Roberts and Warren 1994, Baird 2006). The average weight of individual fish in catches has declined from 70 kg or more to 5-20 kg (Roberts and Baird 1995).The species is thought to contribute around 0.3% of the total fish catch in the lower Mekong (c. 3,030 tonnes per year, ICEM 2010). The species contributes 65% of a large meshed (18-25 cm mesh) fishery just below the Khone Falls in southern Lao PDR, however from 1993 to 1998 it declined from 64 to 27 fish caught per season (Baird 2006).
Healthy subpopulations may only occur in the Mekong basin (Roberts 1992) and, even there, subpopulations have been declining. Subpopulations have been locally extirpated in the Mekong basin (Baird 2006).
The species is believed to benefit from the protection of deep water pools in the mainstream of rivers in the dry season (Baird 2006, Baird and Flaherty 2005).
In 1945, subpopulations had been thought to have been declining for at least the last 65 years (Smith 1945) in central Thailand. Roberts and Baird (1995) reported that just below the Khone falls it had declined by 80-90% between 1970-1995. Roberts and Warren (1994) reported that at Hee Island, above the Khone Falls, 100 individuals used to be caught per day, but that only 60 were caught per day in 1992, and in 1993 only a maximum of 22 were caught per day, and 92 in the whole season. More dramatically, the fishery at Say Island in Champasak Province above the Falls, the fishery for the species crashed in 1993, although in the previous year they had caught 60 fish (Roberts and Baird 1995).
In Malaysia the species has been seriously impacted by dams in the Perak and Terengganu basins, which have destroyed a number of spawning sites (Baird 2006, A.B. Ahmad pers. comm. 2019).
A population decline across the species range in excess of 80% over the course of three generations (30 years) is inferred from catch data from the Khone falls area (Baird 2006), from loss of local subpopulations in the Mekong basin, 69% decline in Malaysian subpopulations over the course of four years (2003 to 2007) (Department of Fisheries (DOF) 2003, Department of Fisheries (DOF) 2007), and from information from other parts of the species range.