The Fish Communities of Lake-Complexes from Danube Delta Biosphere Reserve (DDBR) in Spring-Summer and Autumn of 2016

Abstract

Fish from Danube delta spawn in spring grows over the summer and in autumn season juveniles recruit to the population. Ichthyofauna was sampled in May-July (springsummer) after spawning and September-October (autumn) after the juvenile’s recruitments. A number of 136 fish species are quoted in references for Danube Delta Biosphere Reserve (DDBR) (included marine species) belonging to 3 Classes, 20 Order, and 45 Families (representing more than 70% of Romania's ichthyofauna). Using 4 methods of sampling, from what two in accordance with UE fish sampling standard methods, were sampled 11 representative lakes in 249 stations: electric fishing in 55 sites (fishing effort over 9 hours), 164 sites with multimeshes size Nordic gillnets (4,920 m-net-1·night-1 meaning 29225 m²-net·night-1 fishing effort) plus 23 sites with commercial gillnets (1950 m-net-1·night-1meaning 3758 m²-net·night-1 fishing efforts) and 7 sites using seine fishing (in the Razim lake). In 2016 in 6 lake-complexes were identified 45 species of fish (majority are limnophilic), included Perccottus glenii first recorded in 2016 in Razim-Sinoie lakes-complex. Totally were captured over 60,000 fish individuals with almost 1 t weighting. Using Catch Per Unit Effort (CPUE) for relative biomass grams·h-1 electric or 100 m²-net·night-1, NPUE for relative abundance individuals·h-1 electric or 100 m²-net·night-1) standardization, it was analyzed species richness and ecological parameters, like relative abundance, relative biomass, dominance (D), constancy/frequency (C), ecological significance (W), biodiversity index (Shannon-Wiener indices Hs and Evenness indices E). Present work will characterize the ichthyocoenoses and estimate conservation status of fish fauna from lake-complexes of DDBR. Main fish species, eudominant and euconstant is Alburnus alburnus, characteristic fish species are Scardinius erythrophthalmus and Rutilus rutilus, complementary fish species are Blicca bjoerkna and Perca fluviatilis, mostly species are associate or accessory, but most of them are accidental in lake-complexes, with differences between seasons and sampling methods. The main fish resources species is Gibel carp (Carassius gibelio) with up to 50 % in sampling with commercial gillnets of 50 mm mesh size knot to knot.

Keywords

• fish fauna
• Danube Delta
• lakes
• ecological status