金瓜寮溪翹嘴鮊入侵對魚類群聚之影響

Abstract

本研究在金瓜寮溪的攔砂壩上下游共設四個樣區，以三種垂釣法與一種魚籠陷阱法，進行每月一次的魚類採集，以調查入侵掠食魚類翹嘴鮊對金瓜寮溪原生魚類群聚的影響。 2008年4月至2009年5月間，共發現21種魚類，其中外來種有7種，而翹嘴鮊為其中一種。總合實驗樣區中的採集結果，最優勢種為台灣馬口魚(Candidia barbata)，其次為台灣石魚賓(Acrossocheilus paradoxus)，第三優勢種則為翹嘴鮊(Culter alburnus)，而三者數量佔所有採集魚隻的80.2%。翹嘴鮊雖然分佈攔砂壩以下游流域，但該範圍內原生魚的種類並未減少，而偏好表層活動的台灣馬口魚數量卻較攔砂壩上游顯著減少，僅為上游馬口魚數量的八分之一，並與翹嘴鮊數量呈現負相關，而幼魚部分則壩下游更為上游數量的三十八分之一，數量比例明顯減少。此外，翹嘴鮊消化道內含物分析也發現主要捕食馬口魚的幼魚與亞成魚，推測翹嘴鮊對其捕食壓力甚大，尤其是幼魚；反觀第二優勢種台灣石魚賓在壩下游並未因翹嘴鮊出現而比例明顯減少。總結翹嘴鮊影響攔沙壩下游的馬口魚族群，並使壩下游的魚類群聚出現變化。

This study set up four sampling areas, located in the upstream and downstream of the check dam, in Jingualiao Stream. The researchers conducted field works by employing three types of angling methods and one kind of fish traps to collect fish samples, once per month, to investigate the impact, of the invasive predator, Culter alburnus, posed on native fish communities. To summarize the result in the sampling area, there were 21 different fish species collected in Jingualiao Stream between April 2008 and May 2009. And 7 species out of them are invasive aliens, Culter alburnus, for example. And the first dominate specie is Candidia barbata, followed by Acrossocheilus paradoxus, and Culter alburnus. Above three species take 80.2% of the collected samples. Culter alburnus appears only in the downstream of the check dam and thus did not decrease the number of the native fish species in sampling areas. However, the population of Candidia barbata, in preference of surface water habitats, has decreased significantly below the check dam, and plays 1/8 of the population above the check dam. The population of Candidia barbata community shows negative correlation with Culter alburnus community. The fry population of Candidia barbata shows dramatic difference above and below the check dam, which is one to thirty-eight. Meanwhile, study indicates fry and sub-adult of Candidia barbata as the main component of the digestive tract of the Culter alburnus. Thus, we suggest that Culter alburnus poses great predatory pressure over Candidia barbata community, specifically on fry population, whose habitat is in the downstream of the check dam. On the other hand, Acrossocheilus paradoxus, which habitats in bottom water shows no difference in population structure above and below the check dam. To make a conclusion, Culter alburnus decreased the Candidia barbata population and changed the fish community below the check dam.