Date of Award

2009

Document Type

Thesis - ECU Access Only

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Natural Science

Faculty

Faculty of Computing, Health and Science

First Supervisor

Glenn Hyndes

Abstract

Inland water bodies provide important fisheries resources in Thailand and elsewhere in south-east Asia, yet there is limited information on the biology of important species and catch rates in fisheries, and limited assessment of management strategies such as Freshwater Protected Areas. This study has provided important information on aspects of the biology of knifefish (Notopterus notopterus) and catopra (Pristolepis fasciatus), two dominant freshwater fish species in Thailand, as well as catch and effort trends in the trap fishery and the influence of a Freshwater Protected Area (FPA) on fish communities in Beung Borapet, a large freshwater swamp and an international important wetland in Central Thailand (15ºN; 100ºE).

Both N. notopterus and P. fasciatus were shown to be the most dominant species using traps in fisheries-independent (18.3 and 23.2%, respectively) and fisheries dependent (31.2 and 22.9%, respectively) studies, and were therefore shown to be important species in Beung Borapet. Female N. notopterus reached maturity at 178 mm TL, while female P. fasciatus reached maturity at about 70 mm TL. Both species spawned throughout most of the year, with peak spawning between June and August when rainfall peaked and water levels were rising for N. notopterus and between April and September when water temperature and daylight length were peaking for P. fasciatus. Furthermore, both species are multiple spawners, with the former exhibiting low batch fecundity (approximately 113 and 864 eggs) and the latter showing high batch fecundiy (approximately 10,000 and 62,000 eggs). The high batch fecundity and the daily spawning of P. fasciatus is would result in a high total fecundity for the species. The sex ratio of P. fasciatus exhibited a slight male bias in fish <100 mm, but this reverse to a clear female bias in larger fish. For both species, growth parameters could not be determined using either cohort analyses from length frequency data, or length-at age data from growth increments in hard structures such as scales and otoliths.

The catch composition of the trap and gillnet fishery in Beung Borapet was dominated by five species, namely P. fasciatus, N. notopterus, Oreochromis niloticus, Cyclocheilichthys repasson and Cyclocheilichthys apogon. Traps tended to catch larger fish of more marketable size than gill nets, especially for N. notopterus and O. niloticus. The trap fishery yielded approximately 92 tonnes (2.9 kg/hectare) of fish per year, which was valued at nearly 3 Million Baht (~$US 80,000), which provided an average net income of 83,000 Baht (~$US 2,100) for a fulltime trap fisher in Beung Borapet.

Spatial closure management is a strategy used throughout the world for protecting aquatic biodiversity and promoting fish production. The FPA in Beung Borapet contained lower overall densities and biomass of fish than the fished area, but there were inconsistent patterns among fish species. Some dominant species, such as Cyclocheilichthys enoplos and Amblyrhynchichthys truncatus, had higher densities, while others, such as P. fasciatus and O. niloticus, had lower densities in the FPA. Furthermore, larger sizes of only a few dominant species were observed in the protected zone, e.g. P. fasciatus and N. notopterus. The benefits of the FPA for fisheries enhancement and conservation of biodiversity appear to be limited due to observed illegal fishing activities in the zone as well as higher turbidity related to point-source impacts observed in other studies. Management of the conservation zone in the region requires a combination of top-down and bottom-up approaches and scientific information to improve the effectiveness of FPAs. Fisheries management needs to focus on both the resources and the stakeholders to minimize conflict among different stakeholders and inform them of conservation issues for their natural resources to promote their participation in the management strategies.

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