Scientific Annals of the Danube Delta Institute (Sep 2011)
What fish and how many there are in Danube Delta?
Abstract
The real figure of fish fauna and fishery of the Danube delta is difficult to be estimated due to the limitation in fish sampling and underreporting of catch. This paper proposes to compare output of fish sampling with commercial catch statistics. Fish fauna from Danube delta complex lakes was sampled in 2006-2008 period and catchstatistics represent a long time series data recording. For fish sampling was used two complementary methods: electric fishing for shallow border zone and Nordic gillnet fishing for deep open water. The frequency of occurrence and the dominance in abundance analysis was based on 267 samples including 57158 individuals from both sampling methods since the dominance in biomass was based on 640 kg of fish only from gillnet sampling. In total was sampled 40 fish species, while catch statistics recorded 10 commercial species plus more 3 categories that include more other different species. In the sampling analysis, the most frequent species (very frequent) were perch, bleak, roach, rudd and white bream. The most abundant(eudominant and dominant) species were bleak, roach, rudd, perch, and white bream. In biomass dominate (eudominant and dominant) roach, rudd, perch, white bream, bleak, gibel carp and pike. This analysis shows that Danube delta lakes are dominate by small eurytopic and opportunistic species, favoured by eutrophication of lakes. However, this figure is expression of sampling methods that are limited in estimation of real fish population status. Nevertheless, when this structure is compared to commercial statistics, it is noticed completely other figure. The difference in fish structure may be explained by targeting fishing to large size and high market value fish species. It is not neglected that commercial statistics is deformed by unreported catch sold on black market. According with recorded statistics from 1920 until 2010 the catch trend continuously decrease and species composition was well balanced before 1972 and starting from 1972 until 2010, gibel carp become the dominant commercial species, followed by roach + rudd and bream + white bream. Since, fish estimation based on sampling gives valuable data on actual status of fish structure, catch statistics describe fish evolution and changes in time due to environmental pressure, both analyses are valuable tools in sustainable management of fish resources and for promoting conservation of fish diversity inDanube delta.
