Variations, trends and patterns of fish landings in large tropical reservoirs

Abstract

Temporal variations of fish yields in four major reservoirs in Thailand (Ubolratana; Sirindhorn; Srinakarin; Vajiralongkorn) were investigated with the use of long-term fish landing data ( ‡20 years). The long-term variations in fish yield, measured as the coefficient of variation of yearly yield, ranged mostly between 50% and 100%. For short-term variations, the means of the relative variation (85%) were larger than the absolute variation (63%). This finding indicates that short-term variations were inversely related to fish yield and that a higher uncertainty occurs when fish catches are low. The stocked exotic species exhibited higher variations than the indigenous species. The trend analyses indicated some species had sharply declined fish landings, while some species were quite stable (i.e. reservoir-adapted species). Stocked species tended to increase in relatively shallow reservoirs, compared to the deep reservoir. Fish landing data for each reservoir were patternized, using the self-organizing map, indicating temporal trends of chronological order. The differences among clusters in each reservoir were with respect to the weight of each species in the fish landings in each year, and temporal changes in species composition in the reservoirs, which would primarily be attributed to the environmental changes followed by anthropogenic pressures. The mean trophic level (s) fluctuated, resulting from changes in species composition and weight of fish landing, as well as fish stocking programmes.

Larval fish assemblage patterns in three tributaries of Mekong River in Thailand

“…The regulated Gam River formed a unique larval fish assemblage pattern. This assemblage was dominated by larvae of the adults that are commonly found in reservoirs (Jutagate et al, 2012;, which implies a lentic environment between each dam in the series. The lowest contribution to %OP of the white fish larvae, compared to any other cluster, would indicate that only few adults of white fishes, such as Mystacoleucus spp.…”

Diversity and Community Structure of Fishes in the Regulated Versus Unregulated Tributaries of the Mekong River

“…Dams disrupt movements of not only fish but also other materials like nutrients (Jackson and Marmulla, 2001). After impoundment of large reservoirs in Thailand, black fish commonly increased in abundance, but they did so only for a certain period because nutrients trapped in the reservoirs only temporarily enhanced algal production (Jutagate et al, 2012). Although some grey and even white fish, such as eight species in Table II, are also known to colonize reservoirs, they typically exhibit slow growth, delayed maturity and smaller fecundity, likely because of the reduced food availability associated with the loss of annual flood pulse (De Graaf, 2003;Suvarnaraksha et al, 2011) and reduced water velocity (Penczak, 2007), significantly affecting local fishery production (Welcomme and Halls 2004;Alford and Walker, 2013).…”

Spatio-temporal variations in abundance and assemblage patterns of fish larvae and their relationships to environmental variables in Sirindhron Reservoir of the Lower Mekong Basin, Thailand

“…Alteration of fish assemblages and loss of fish diversity are among the major impacts of river damming. A common alteration is the change from a fish community dominated by riverine species to one dominated by lacustrine species, which eventually leads to the local extirpation of many riverine fish species (Kruk and Penchack, 2003;Jutagate et al, 2012).…”