| Summary: | 碩士 === 國立高雄海洋科技大學 === 海洋環境工程研究所 === 92 === Abstract
This study is aiming to investigate the community structure of larval fishes in the Hoping estuary, Hualien, Taiwan. Attempts were also made to elucidate its temporal variations in relation to the hydrographic factors of ambient waters. Samples were collected with a push net of traditional larval fisheries on a seasonal basis in the time period of February 2001 – November 2003. The results showed that the community was composed of variety of larval fishes, including 195 species, 157 genera, 89 families. Based on their ecological features, they could be categorized into 6 groups, i.e., migratory species, inshore species, rocky species, coastal-estuarine species, demersal species and deep-sea species. Among these groups, the specimens of migratory species were the most abundant, while the demersal fishes were rich in species number. The abundance of migratory species and also the richness in species composition of the study waters were probably associated with the Kuroshio current which passes through the east of Taiwan. Nevertheless, the top 14 dominant species comprised 76.8% of the total catch, i.e., Encrasicholina heteroloba, Saurida elongate, E. punctifer, Sardinella hualiensis, Liza macrolepis, Thryssa setirostris, Trichiurus lepturus, Gerres abbreviatus, Valamugil cunnesius, Benthosema sp., Sillago japonica, Megalops cyprinoids, Gazza minuta and Tripterygiidae sp. Among them, the E. heteroloba was the most abundant species, comprising 60.7% of total catch. The peak abundance of this species during August-October is possibly a result of the strong southwestern wind in summer months, which carries the South China Sea Water with the larvae of E. heteroloba crossing the south end of Taiwan to join the Kuroshio current, and then carries them northward up to the study waters. According to the monthly abundance of each species, these fish larvae were categorized into 5 groups, probably reflecting the differences in their spawning seasons. Furthermore, based on the species compositions of monthly samples, these samples could be clearly categorized into three groups, i.e., Group A, B and C. The Group A and B consists of samples mainly collected during January-May and June-November, respectively. However, the Group C includes samples from April-August 2001 only. The Canonical Discriminant Analysis was applied to examine the segregation of Group A, B and C in relation to the hydrographic factors, and consistent results were obtained. The Group C is coincided with water of low salinity and high suspended solids content, which occurred only in 2001 when rainfall was reported to be higher than the other two years. The segregation of Group A and B is found to be associated with significant difference in water temperature (p<0.05), which may simply reflect the seasonal variations in the environmental conditions and also the spawning habits of varied fish species. In general, the larval fish community in the Hoping estuary can be categorized into winter-spring group and summer-autumn group. The appearance of scarce species in large numbers, accompanied with the disappearance of some estuarine species is highly related to the water of low salinity and high suspended solids content when heavy rainfall occurs.
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