engleski

Structure of fish community in lake Vrana on island Cres, Croatia

Fish samples were collected 4-5 times per year from February 1996 to September 1997. The dominant fish species is Rudd (Scardinius erithrophtalmus: 76,37% of individuals), which is assumed to be a native in this lake. The other fish species are: Pike (Esox lucius), Tench (Tinca tinca) and Chub ,(Leuciscus sp.), all introduced species. Lake Vrana is an oligotrophic lake with potable water and it seems quite unusual that only four fish species live here. The lake has an area of 5.75 km2, a maximum depth of 76 m, and a water volume of ca. 220 million m3. It is a cryptodepression, which has a bottom 62-m below, and a surface 11-14 m above sea level. It is situated in southwestern Croatia, on the island of Cres. In the literature, we found records of eel presence (Anguilla anguilla), but in the last twenty years there were no records of eel being caught or observed. Species diversity measures are expressed through different indexes: Shannon-Wiener index is 1.137 of possible maximum 2.0, Whitaker plots of species abundance are given (Alpha=0.5910, x=0.998847), Simpson's (1-D=0.396) and Brillouin's (H=1.115) indexes are also given. The uniqueness of this lake is its large number of big fish, due to low fishing pressure. The oldest Rudd documented in this research was more than 12 years old, and weighed over 2.7 kg. The biggest Chub weighed 2.6 kg, while the biggest Tench specimen was 3.2 kg.

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