Fish fauna and structural change of the fish community as a result of ecosystem disturbance were surveyed in the Nakdong River system, Korea, from March 2005 to October 2010. In total, 80 freshwater fish species comprising of 56 genera, 24 families we...
Fish fauna and structural change of the fish community as a result of ecosystem disturbance were surveyed in the Nakdong River system, Korea, from March 2005 to October 2010. In total, 80 freshwater fish species comprising of 56 genera, 24 families were collected from the present survey. Of them, the 39 cyprinid fish species corresponding to 48.8% were found most in abundance, of which RA was 84.1%. The second was the cobitid species with the 7 observed species corresponding to 8.8%, of which RA was 6.5%. Among the 80 species, 29 species (36.3%) were identified as endemic species to Korea. It corresponds to 46.0% out of 63 endemic species ed in Korea so far.
Five endangered fish species as designated by the Ministry of Environment, five exotic species and twelve translocated species which is introduced from other native rivers were found from the Nakdong River system. The dominant species was Zacco platypus (RA: 23.3%) and the subdominant species was Zacco koreanus (RA: 20.6%) in the whole Nakdong River system. This showed a change from the middle 1990's when Zacco koreanus was the dominant species, and Zacco platypus was the subdominant species. In addition, the population size of exotic species, introduced into the Nakdong River, has increased significantly whereas, the population size of acheilognathin and the small size species of cyprinid and cobitid fish were significantly smaller.
As a result of analyzing the fish community in the Nakdong River, inhabitant species and diversity indices of upper-mid reach of main channel were 22 to 31 kinds and ranged from 0.974 to 1.056 as high, respectively. The findings showed that 1st major tributaries had higher species diversity indices that of 0.881-1.333, than the 1st small tributaries with 0.492-0.890. It showed that 1st major tributaries are consisted of various species and have a stable community structure. In other words, the long and wide river basin area have more than 30 species and it formed relatively stable community of more than 1.0 diversity. To carry out a cluster analysis based on the distribution of fish, the main channel, 1st main tributary and 1st small tributary were divided into 6 clusters within 35% similarity. In case of the main channel of the Nakdong River system, population was generally well separated as most upper reach area, upper reach area, upper-mid reach area, mid-lower reach area, lower reach area and most lower reach area. In addition, 1st small tributaries and 1st major tributaries were well separated onto their group. The common species(constancy 100%) of the 1st major tributaries in the Nakdong River were 12 species : Carassius auratus, Pungtungia herzi, Squalidus gracilis majimae, Hemibarbus labeo, Rhynchocypris oxycephalus, Zacco koreanus, Zacco platypus, Misgurnus anguillicaudatus, Cobitis hankugensis, Coreoperca herzi, Odontobutis platycephala and Rhinogobius brunneus.
On the survey of the backswamp and marsh in the Nakdong River system, endemic species and subspecies had the highest percentage (8 species, 34.8%) in relative abundance, and exotic species had the lowest percentage (2 species, 8.7%) in the Gudam backswamp. It indicates that the native fish community was found to be well-maintained. The proportion of introduced species was very high (11 species, 35.5%) in the Dalseong backswamp, which is adjacent to metropolitan areas. This shows that a disturbance of the fish community has taken place to a high degree.
In the diversity index aspect, the upstream place (0.703) of the aggregate collection point of Naeseong stream (which is a branch of the Nakdong River) has a higher diversity index than that of the aggregate collection point and the downstream point (0.572-0.596). The result could be interpreted that the river bed disturbance are due to the aggregate collection and the resulting suspended solids affected the diversity of the fish community. In Wi stream, there was observed similar river bed disturbance. In the mid-reach of the Nakdong River(Oekwan), the species diversity index was low (0.372) and dominant index was high(0.536) around the sand stope area. Stations of upper reaches and lower reaches have high species diversity indices of 0.943, 0.814 and 0.864 respectively. This proves that disturbance of the riverbed caused by sand mining has an influence on the diversity of the fish community. In the biomass aspect, the fish biomass was high(10,456 g) around upper reaches of the sand stope area. Sand mining had been disturbing the river ecosystem of the study station, and this station showed a quite low biomass (2,665 g). It seemed that biomass was recovered from the sand mining area toward the lower reach of the Nakdong River. Conclusively, sand mining disturbs the fish's habitat such as a river bed and leads to some influence on the fish community and species composition in a short period of time.
As a result of surveyed in the Imha, Yeongcheon, and Unmun lake, it was found that dominant or subdominant species were found in lotic water, such as Zacco koreanus, Zacco platypus, Squalidus gracilis majimae, Microphysogobio yaluensis, Puntungia herzi, Coreoleucoscus splendidus, Cobitis hankugensis, Odontobutis platycephala, Rhinogobius brunneus, in the river of the planned dam region. However, in lotic water fish disapeared and the fish fauna changed in lentic water, after construction of the dam. It showed that the number of inhabitant species reduced despite the presence of introduced species from outside after construction of the dam. In addition, if the inflow river was relatively long and wide, it revealed that the rate of survival of inhabitant species before the construction of the dam was higher. Even if they formed dominant species because of increasing population of introduced fish species, formed dominant species was decreased in a short period of time in dam reservoir. A small number of dominant species group occupied most of the fish populations.
459 specimens of large mouth bass (M. salmoides), exotic species, were collected at 44 sites in the main channel and the tributaries of the Nakdong River and showed that they were most widely distributed. Also, in the mid-1990s, the piscivorous chub (O. uncirostris amurensis), which is an introduced species from an other native river, was widely distributed in the Nakdong River system, and the density of population has increased rapidly in the middle reach of the Nakdong River. Regarding Micropterus salmoides, they feed mainly on aquatic insects when they are below one age and then selectively feed on fish only over age one. In the stomach contents of Opsariichthys uncirostris amurensis, the most important prey items were small size fish species, including some juvenile of larger size species. So, It was decided that biological factors are disturbing the native fish community.
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