Thanitha Thapanand's research while affiliated with Kasetsart University and other places

The ecosystem of Bandon Bay, in the Gulf of Thailand (GoT), has been impacted since 2007 by the continued stocking of larval blue swimming crab Portunus pelagicus, also called a crab bank. In this study, the food web in the Bay was modelled using Ecopath software to compare the trophic status, interaction and energy flow among the components in the system in 2007 and 2016 (i.e., before and 10 years after the crab bank intervention). The models were based on data collected from trawling. Twenty fish and shellfish components were used in the 2007 model, while 22 were used in the 2016 model. A significant increase in biomass was found in blue swimming crab, but biomass declined for other demersal fishes, cephalopods, and Penaeid shrimps. The production/biomass ratios of most components were higher in 2016 but the consumption/biomass ratios were relatively unchanged. The ecotrophic efficiency indicated that shellfishes were more exploited than fishes. Changes in most of the ecological indices revealed higher maturity and stability after 10 years of crab bank operation. The mixed trophic impact indicated bottom-up regulation, and that the increase of blue swimming crab negatively impacted only Mantis shrimp. Overall, the results indicate positive impacts of the crab bank intervention.

Population dynamics of Bocourti’s catfish (Pangasius bocourti), in the Mekong River at Nong Khai Province, was studied, using the length frequency data (LFD) to evaluate the von Bertalannfy’s growth function (VBGF), mortality coefficients, recruitment pattern, fishery-exploitation rate (E), relative biomass per recruit (B’/R) and relative yield per recruit (Y’/R). The samples were collected monthly by using gillnets of mesh size; 4, 7, 9 and 14 cm (stretched mesh), during September 2007 to October 2008. The obtained parameters from the seasonalized VBGF, which was fitted to the LFD, were: asymptotic length = 57.62 cm TL, curvature parameter = 0.56 yr-1, the theoretical age at length zero = -0.0163 yr-1, amplitude = 0.7 and winter point = 0.9. The life-span of P. bocourti was estimated at 5.35 year. The instantaneous total, natural and fishing mortality coefficients were 2.21, 1.04 and 1.16 yr-1, respectively. These mortality coefficients yielded the current E at 0.53. The length at first capture (Lc) was estimated at 23.55 cm. The recruitment pattern was one peak in a year. The exploitation rate at 50% of the unexploited B’/R was 0.34. Meanwhile, the estimated Y’/R at maximum exploitation rate was 0.64, which was still beyond the current exploitation rate. It is, therefore, implied that increasing more fishing effort of P. bocourti fisheries in this fishing ground is possible. Keywords: population dynamics, bocourti’s catfish, Pangasius bocourti, Mekong River, Thailand

Bocourti’s catfish was monthly sampled by gillnet during September 2007 to October 2008 in the Mekong River, Nong Khai Area. Sampling area consisted of five stations. A total of 2,673 fishes were captured. The results showed that the relationship between total length and body weight, which have length ranged from 9.3 - 55.4 cm, was W = 0.0077TL3.0056 and complied isometric growth pattern. The relative condition factor (Kn) of male and female were 1.23 ± 0.09 and 1.27 ± 0.21, respectively, and showed seasonal variable. The size at first maturity of male and female were 24.41 and 23.28 cm. The spawning season was between April to June. The average diameter was 1.15 ± 0.86 mm. and the average fecundity was 95,671 ± 99,285 eggs. The relationship between fecundity and total length was Fe = 0.0115TL4.1330. The results from studies can be further applied for the economic culture, conservation and management of the bocourti’s catfish in the Mekong River. Keywords: Bocourti’s catfish, Pangasius bocourti, Reproductive Biology, Mekong River.

Abstract The trophic dynamics of a newly-impounded south east Asian reservoir, Pasak Jolasid, Thailand, monitored from its creation, were constructed using ecopath, a mass-balanced model. The trophic levels (TLs) of 36 ecological groups varied between 1.0 and 3.2. The majority of fish biomass was at the second TL, where the fishery is concentrated. Some food resources (benthic organisms and zooplankton) were not fully used, whereas phytoplankton and benthic algae were important components of the food web, which is based on phytoplankton and detritus. The implications of these findings are discussed in terms of ecological maturity of the ecosystem and possible fishery management of this multi-purpose reservoir.

The aim of this paper is to study and quantitatively describe the trophic relationships in a newly impounded South East Asian reservoir (Pasak Jolasid near Bangkok, Thailand), for the management of the multispecies fishery of this reservoir. Ecopath was used to construct a mass-balance model, which is considered to be the first step in summarizing ecological and biological information in a coherent framework through trophic networks in the lake. Various socio-economic and ecological objectives were examined, using Ecosim, for an optimization of the economic value of the ecosystem, the job opportunities associated with various fishing gears, and the abundance of each fish group for their economic or intrinsic ecological value strategies. The implications of the findings are discussed in terms of fisheries management of the ecosystem. The Ecospace routine allowed some hypothesis to be assumed on the future spatial distribution of the fish groups and the fishing effort; the potential importance of the preservation of littoral zones is particularly emphasized and the implications for water use of the dam are discussed.

The reproductive ecology of shark catfish Helicophagus waandersii in the Mun River, the largest Mekong tributary in Thailand, was studied from July 2003 to December 2004. The aim of the study was to determine whether shark catfish, which contribute greatly to fish catches, benefits in terms of spawning, from the management regime of the Pak Mun Dam to open all sluice gates annually for 4 months during the rainy season. In total, 228 females were studied. The highest average gonadosomatic index (4.42% ± 1.90%) was observed in the rainy season in June 2004. Fecundity ranged from 21 550 to 191 540 eggs. Three hormonal profiles viz. testosterone (T), 17 β-estradiol (E2), and 17, 20 β-dihydroxy-4-pregnen-3-one (17, 20 βP) were determined by radioimmunoassay. The highest levels of T (0.96 ng ml−1), E2 (14.37 pg ml−1), and 17, 20 βP (0.81 ng ml−1) were respectively measured in April to May, July, and May. Changes in the maturity stage and the annual sex hormonal profiles revealed that the spawning period of H. waandersii is from May to June. There was no spatial statistical difference (p > 0.05) for each sex steroid profiles. The results indicated that H. waandersii spawn during the rainy season in the rapid areas, both downstream and upstream, and the sluice gates opening management regime for 4 months in the rainy season is of advantage for H. waandersii in terms of feeding and nursery grounds in the upstream area. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract  Spawning biology and migration of the mud crab, Scylla olivacea (Herbst), in the Andaman Sea were examined from November 2002 to March 2004 at Klong Ngoa Mangrove area, Ranong Province, Thailand. Mature females were dominant from July to November. The changes in monthly gonadosomatic index of females ranged from 1.9 (±3.3) to 8.2 (±5.8) and size at first maturity was 9.4 cm internal carapace width (ICW). Fecundity (F) correlated ICW according to F=3.02 ×ICW2.98. A total of 1013 female crabs were double tagged with spaghetti and bottom tags. The recaptured rate was 36.7% and showed that females migrated from coastal area to the open sea during the spawning season. A closed season during the north-east monsoon season and a minimum legal ICW size of 10 cm are recommended for sustainable management of the fishery.

Summary (En) 2 ill., 1 table