Journal of Environmental Protection and Ecology 12, No 3, (2011)

Transcription

1 Journal of Environmental Protection and Ecology 12, No 3, (2011) Water pollution Characteristics of Freshwater Fish Population in the Danube River Near Braila within the Period L. Florea Faculty of Food Science and Engineering, Department of Fishing and Aquaculture, Dunarea de Jos University of Galati, 47 Domneasca Street, Galati, Romania Abstract. The composition of freshwater fish populations is closely linked to the environmental conditions. Between the environmental conditions in the Danube river were highly affected by direct and indirect anthropogenic activities. In the human impact on fish populations was diminished. The analysis of freshwater fish characteristics relies on recorded catch that lay at the basis of six indicators describing the status of the freshwater fish community. We analysed the following indicators of freshwater fish community: (1) the total annual catch of fish species (t/year); (2) the total number of fish species caught by industrial fishing, fishery statistics (number of species/year); (3) the number of valuable fish species (relative biomass RB>1%) annual catch (number of species/year); (4) the number of ruling fish species (RB>10%) annual catch (number of species/year); (5) the annual relative biomass of feeding groups (% planktivorous species/year, % benthivorous species/year, % top carnivorous species/year, % eurytroph species/year); (6) the annual relative biomass of reproductive groups (% semi-migratory species/year; % rheophilic species/year, % limnic species/year). This analysis highlights that in the fish community structure come out to be in a rebalancing process. Keywords: the Danube river, Braila, fish population. AIMS AND BACKGROUND The aim of this paper is to analyse the qualitative and quantitative structure of freshwater fish populations from the Danube river, near Braila, within period. The composition of freshwater fish populations in the Lower Danube is closely linked to the environmental conditions in the main channel and its floodplains. During and after this period human impact on fish populations was strong due to an increase of direct (fishing) and indirect pressures (impoundment, canalisation, urbanisation and industrialisation, corporate production and livestock, hydrotechnical works, transport) 1. Freshwater fish have different strategies to accomplish vital functions such as reproduction and feeding 2. The freshwater fish species of the Lower Danube river are reclassified according to feeding habitats 814

2 and type of food 3 into four feeding groups and follows reproduction criteria into three reproductive groups 4. EXPERIMENTAL In the Danube river between Braila town (route kilometer (rkm) 170) and Giurgeni village (rkm 238), we investigated the changes of six indicators describing the status of the freshwater fish community by analysing the catch, both, in river canal and its floodplain areas, in two different periods, the present period ( ) and the former period ( ). In these periods the gillnet fishing was used in the running water of the Danube river and trapping methods were used in lentic water of floodplain area. Annual fish capture is taken over from different bibliographic 5,6 and statistic 7 sources. The freshwater fish species of the Lower Danube river are put together according to feeding habitats and type of into four feeding groups: planktivorous species (P), benthivorous species (B), top carnivorous species (C) and eurytroph species (E) and according to reproduction criteria in three reproductive groups: semi-migratory species (S), rheophilic species (R) and limnic or lentic species (L) (Table1). RESULTS AND DISCUSSION The analysis of freshwater fish characteristics relies on recorded catch from fishery statistics that lay at the basis of six indicators describing the status of the freshwater fish community from the Danube river, near Braila. We attempted to describe and analyse these six indicators for present period ( ) comparative with the previous period ( ), and also for the previous period we analysed these indicators comparative for the Danube river channel and for its floodplain areas. The Danube river channel, between Braila town (rkm170) and Giurgeni village (rkm 238), has a total length of 118 km and a total surface of 6160 ha. The floodplain areas, between Braila town (rkm 170) and Giurgeni village (rkm 238), has a total terrestrial surface of ha from which the aquatic surface is 4465 ha. The indicators of freshwater fish community are analysed to light out the situation in the Danube river channel for the present period ( ) comparatively with the previous period ( ) both for the Danube river channel and for its floodplain areas. 815

3 Table 1. Feeding and reproductive groups of freshwater fish species in the Danube river near Braila (rkm ) Feeding groups Species Reproductive Species groups scientific name common name scientific name common name Planktivorous spe- silver carp cies (P) place of feeding is water column type of food is phytoplankton, zooplankton Hypophthalmichthys molitrix Aristichthys nobilis Pelecus cultratus bighead carp ziege bleak Benthivorous species (b) place of feeding is bottom type of food is benthic invertebrates, submerged vegetation, epyphyton, detritus Blicca bjorkna Abramis sapa Aspro streber Acerina schraetser Chondrostoma nasus Acipenser ruthenus Barbus barbus Vimba vimba Misgurnus fossilis Tinca tinca Lotta lotta Ctenopharingodon idella common carp common bream white bream white-eye Danube streber schraetzer sneep sterlet barbel vimba weatherfish tench burbot grass carp Semi-migratory species (S) species that live in rivers and, in spring, move into lakes to reproduce in summer or autumn Stizostedion lucioperca Blicca bjorkna Pelecus cultratus Leuciscus idus common carp wels catfish pike-perch common bream white bream ziege ide bleak to be continued 816

4 Continuation of Table Top carnivorous species (C) place of feeding is water column and bottom type of food is other fish, macroinvertebrates Stizostedion lucioperca Esox lucius Perca fluviatilis Acerina cernua Wels catfish pike-perch northern pike european perch ruffe Rheophilic species (R) species that live, feed and reproduce permanently in running water. Incidentally they migrate into lakes Barbus barbus Vimba vimba Aspius aspius Acipenser ruthenus Hypophthalmichthys molitrix Aristichthys nobilis Chondrostoma nasus Abramis sapa Tinca tinca Aspro streber barbel vimba asp sterlet silver carp bighead carp sneep white-eye bream burbot Danube streber Eurytroph species (E) place of feeding is water column and bottom type of food is a significant amount of plant and animal material Leuciscus idus Carassius auratus Carassius carassiu Aspius aspius Scardinius erythrophthalmus ide goldfish crucian carp roach asp rudd Limnic species (L) species that live and reproduce permanently in lakes or in slowly flowing river stretches Carassius carassiussius Carassius carassiussiu Carassius carassiussius auratus Perca fluviatilis Acerina cernua Esox lucius Tinca tinca Scardinius erythrophthalmus crucian carp goldfish european perch ruffe northern pike tench rudd roach 817

5 (1) The total annual catch of fish species (t/year) shows a long-term fluctuation of fish caught in the Lower Danube near Braila. It is obvious that the biggest catch was recorded, in all these years, in floodplain areas, the highest catch recorded in 1978 was about t, that means 10.6, respectively 12 times higher than the biggest catch from Danube river channel between , respectively The average catch recorded in floodplain areas was 8.3, respectively 8.5 times higher than in the Danube river channel between , respectively The catch recorded in the Danube river channel seems to be similar between , respectively (Fig. 1). minimum medium maximum annual catch (t) Fig. 1. Annual catch (minimum, medium, maximum) in different periods ( and ) and different areas (the Danube river channel and floodplain areas) (2) The total number of fish species annual caught by industrial fishing, (number of species/year) is generally an indicator of fish biodiversity but in this case an indicator of fish availability. The figures show that the availability for fishing of freshwater fish species increased in the present period From an average number of fish species of 11.7, respectively 14 annual caught by industrial fishing between in floodplain areas, respectively in the Danube river channel, in the present period this indicator rose up to 16.3 (Fig. 2). minimum medium maximum total number of fish species annual catch Fig. 2. Total number of fish species annual caught by industrial fishing (minimum, medium, maximum) in different periods ( and ) and different areas (the Danube river channel and floodplain areas) (3) The number of valuable fish species (species with relative biomass RB>1%) annual catch (number of species/year) is an indicator of fish community structure, the higher the better. The analyses made in all these three periods light out that

6 the better fish community structure is between , when the average of this indicator of 11 is 1.4, respectively 1.8 times higher than in the Danube river channel, respectively in floodplain areas between (Fig. 3). minimum medium maximum number of valuable (RB>1%) fish species annual catch Fig. 3. Number of valuable fish species (species with relative biomass RB>1%) annual caught by industrial fishing (minimum, medium, maximum) in different periods ( and ) (4) The number of ruling fish species (species with relative biomass RB>10%) annual catch (number of species/year) is also an indicator of fish community structure, the higher the better. The better fish community structure is between , the average number of ruling fish species was 4 comparative with 2.3, respectively 1.99 in the previous period in the Danube river channel, respectively in floodplain areas (Fig. 4). minimum medium maximum number of ruling (RB> 10%) fish species annual catch Fig. 4. Number of ruling fish species (species with relative biomass RB>10%) annual caught by industrial fishing (minimum, medium, maximum) in different periods ( and ) The occurrence and number of ruling fish species (3) is a good indicator of diversity of economically important fish. Table 2 where the fish species are arranged in decreasing order of their relative biomass shows a significant change of the ruling fish species which had a relative biomass higher than 10% in less of 1 year of the corresponding period. The average relative biomass during the four periods ( , , , ) shown in another list of ruling fish species (Table 3). 819

7 Table 2. Ruling fish species (RB>10 %) in less of 1 year of the corresponding period Floodplain Gura Garlutei Stizostedion lucioperca Esox lucius Blicca bjorkna Floodplain Navodari Floodplain Fundu Mare Blicca bjorkna Danube river channel Blicca bjorkna Barbus barbus Aristichthys nobilis Esox lucius 820

8 Table 3. Ruling fish species (RB>10 %) over the corresponding period Floodplain Gura Garlutei (29.84 %) (21.95%) (12.2%) (62.16%) (10.92%) Floodplain Navodari (43.23%) (28.76%) (10.80%) Floodplain Fundu Mare (56.14%) (17.01%) (68.44%) (17.53%) (67.11%) (11.27%) (52.48%) (2.98%) (20.32%) (18.76%) (10.80%) Barbus barbus (9.22%) Danube River channel (42.31%) (28.17%) (32.11%) (10.62%) 821

9 (5) The annual relative biomass of feeding groups (% planktivorous species/ year, % benthivorous species/year, % top carnivorous species/year, % eurytroph species/year) is rather different for the three analysed periods. The abundance of eurytroph species and a low presence of top carnivorous species in previous period confirm the unbalanced structure of the fish community in this period. For the present period, , the significant presence of top carnivorous species shows a resilience process (Fig. 5). other species top carnivorous species euritrophic species planktivorous species benthivorous species relative biomass (% /year) Fig. 5. Relative biomass average (%) of feeding groups in different periods ( and ) and different areas (the Danube river channel and floodplain areas) (6) The annual relative biomass of reproductive groups (% semi-migratory species/year; % /year, % limnic species/year) lights out a very significant changes for rheophilic species which are well represented in the present period. The semimigratory species are also well represented in the present period (Fig. 6). other species limnic species reophilic species semi-migratory species relative biomass (%/year) Fig. 6. Relative biomass average of reproductive groups in different periods ( and ) and different areas (the Danube river channel and floodplain areas) CONCLUSIONS The data on fish catch recorded in the Danube river channel and its floodplain areas in the previous periods represent an extremely valuable reference for the comparative study of fish community changes. The comparative analyses of the six indicators of freshwater fish populations show a highly unbalanced structure of the fish community for the previous periods and a resilience process for the present period. In the human impact on fish populations diminished 822

10 because fishing was banned in floodplain areas, economic activities decreased and new legislation on environmental protection came into force. REFERENCES 1. A.VADINEANU: Past and Future Management of Lower Danube Wetlands Systemm.A Bioeconomic Appraisal. The J. of Interdisciplinarry Economics, 14, 415 (2003). 2. C. LEVEQUE: L habitat: etre au bon endroit au bon moment? Bull. Fr. Peche anad Pisciculture, 337, 9 (1994). 3. P. BANARASCU: Romanian Fauna. Pisces Osteichthhyes. Vol. XIII, Ed. Academiei Republicii Populare Romane, Bucharest, T. OBERDORFF, E. GUILBERT, J. C. LUCCHETTA: Patterns of Fish Species Richness in the Seine River Basin, France. Hidrobiologia, 259, 157 (1993). 5. I. ARDELEAN, E. ARION-PRUNESCU, C. A. BANU, P. BANARESCU, J. BOISNARD, Gh. BREZEANU, Th. BUSNITA, V. ENACEANU, A. MAIANU, M. MARINESCU, C. MO- CIRNITA, Gr. OBREJAN, M. OLTEAN, I. POPESCU-ZELETIN, L. RUDESCI, Al. V. STA- NESCU: Study on the Limnology of the Romanian Danube Sector. Ichtiofauna. Ed. Academiei Republicii Socialiste Romania, 1967, L. FLOREA: Contributions to the Study of Fish Population Distribution in the Small Island of Braila, Indicator for Assessing the General Condition of Hydraulics. Ph. D. Thesis, Dunarea de Jos University, Galati, 1998, ANPA: National Administration Fisheries and Aquaculture. Commercial Catch Statistics, Received 24 February 2009 Revised 30 May