Mollusc fisheries and length–weight relationship in Tonle Sap flood pulse system, Cambodia

Abstract

Molluscs are important for ecological function, livelihoods and fisheries, but are often forgotten in research and management. Here, we investigated intra-annual variation in the landing and growth patterns of three mollusc species, i.e., Corbicula moreletiana, Pila virescens and Pila ampullacea, using one-year daily data on landing catches and values, recorded in Kampong Chhnang province of Tonle Sap (TS) Lake. Overall, 8330 tonnes with a first sale landing value of US$ 1.4 million for the three species were reported. Also, we found that C. moreletiana was abundant during the dry season with high temperature and less precipitation. By contrast, the two Pila species were abundant from the early rainy to early dry seasons when precipitation and water levels increase. The length–weight relationship analysis indicated that a faster growth in weight of Pila species occurred in the rainy season, and a general negative allometric growth was observed for the three species. This implies that their populations were intensively fished. Our preliminary results suggest that molluscs in the TS Lake (i) are important resources in support of people's livelihoods, (ii) respond differently to intra-annual variation in temperature, precipitation and hydrology and (iii) are being intensively exploited with significant reduction in growth rate. Therefore, it is necessary to conduct further comprehensive research describing status of mollusc stocks and their ecology to support long-term management and conservation of this important aquatic fauna. Our study contributes to establishing the first important baseline data and information on key mollusc species for the TS.

Annotated checklist of freshwater molluscs from the largest freshwater lake in Southeast Asia

“…Pila gracilis seemed to be rare in the eastern Thai provinces that border Cambodia (Ng et al in press) but appears to be common in the Tonle Sap basin. Although Pila gracilis was not previously recorded as being harvested from the Tonle Sap Lake (Ngor et al 2016(Ngor et al , 2018d, we recorded Pila gracilis being sold together with Pila pesmei (Morlet, 1889) and Pila virescens (Deshayes, 1824) at one landing site in Kampong Chhnang Province, and collected Pila gracilis and Pila virescens from within the Lake.…”

“…4D), and is often sold in markets and roadside stalls. An annual harvest of more than 1500 tonnes of the species was recorded from five commercial landing points in Kampong Chhnang Province (Ngor et al 2018d).…”

“…In addition, there has been interest in economically-important molluscs, including freshwater apple snails ( Ampullariidae ) and Asian clams ( Cyrenidae ) ( Ngor et al 2014 , 2016 , 2018d ). The composition of ampullariids in the Tonle Sap Lake appears to vary seasonally, probably owing to the vastly different climatic and hydrological conditions ( Ngor et al 2018a , d ).…”

“…In addition, there has been interest in economically-important molluscs, including freshwater apple snails ( Ampullariidae ) and Asian clams ( Cyrenidae ) ( Ngor et al 2014 , 2016 , 2018d ). The composition of ampullariids in the Tonle Sap Lake appears to vary seasonally, probably owing to the vastly different climatic and hydrological conditions ( Ngor et al 2018a , d ). There is also growing concern about the economic and ecological impacts of invasive apple snails, Pomacea species, which were not established in Cambodia two decades ago ( Cowie 1995 ), but are now spreading rapidly, including in the Tonle Sap Lake ( Ngor et al 2014 ; Khay et al 2018 ; Ngor PB, pers.…”

Length–weight relationships of bivalve species in Italian razor clam Ensis minor (Chenu, 1843) (Mollusca: Bivalvia) fishery

“…areas are in fact conditioned by different variables, which can be abiotic (environmental) or biotic (physiological) (Gaspar et al 2002), although in the present study these variables were not taken into account. Growth patterns also vary considering different life stages (Gaspar et al 2002) and seem to vary even within the year, as demonstrated by different b values in monthly length-weight relationships (Tirado & Salas 1998;Ngor et al 2018). Between the North Adriatic and the Central Tyrrhenian Sea, a possible hypothesis explaining this difference may be related to latitude (Beukema & Meehan 1985), depth, type of bottom (Claxton et al 1998) and/or type of sediment (Newell & Hidu 1982).…”