V. MUŽIK
Slovensky rybársky zväz, A. Kmeta 20, SK 010 55 Žilina, Slovakia
Recreational fishing in Slovakian rivers is influenced by a number of factors related to human activities in the basin.
Pollution
The overall quality of water in Slovakian rivers has improved in recent years. During the 1960s and 70s a significant proportion of mountain streams was permanently polluted, especially by industrial effluents. In many cases the level of pollution was such as to render the rivers fishless. Improvements in water quality were achieved by the construction of a network of purification plants throughout the country in the 1980s. Fish populations have been re-established by programmes of intensive stocking in the river basins, principally the Vah from Ruzomberok to Žilina, the Hron from Podbrezova to Ziar nad Hronom, and the Slana around Gemerska Horka, Ondava and Poprad. The situation is still critical in the Nitra river below the town of Novaky due to heavy pollution from a chemical plant. Further sources of pollution are agricultural wastes, dung, manure, pesticides and fertilizers, which together with industrial effluents were contributing to “global area pollution”.
At present the use of agro-chemicals has been reduced due to the changing financial situation of the country. The reduction in pesticide and fertilizer use has had a positive effect on water quality particularly in submontane rivers where eutrophication has declined and the build up of submersed vegetation has decreased. Chemical pollution includes acid rain whose effects are particularly severe in enclosed waters. However, the impacts on the ichthyofauna have not yet been evaluated.
Accidental fish kills due to non-recurring escapes of toxicants occur every year. Most such damage originates from the food processing industry and the chemical industry which are together responsible for over half such incidents. Annual damage of this type is reckoned to amount to more than Sk 5.7 million.
The local branches of the Slovak Fisheries' Union have an adequate legal framework for claiming compensation for environmental damage. Two types of damage are recognized:
Direct poisoning caused by non-recurring accidental release of toxicants into the river.
Permanent pollution caused by continuous discharge of toxic effluents into the river over a longer period producing a gradual worsening of water quality and the deposition of contaminated substrates on the river bed. Such pollution produces fishless zones of up to 50 km in some rivers.
Fish kills are recorded by the State Administration based on information provided by recreational fishermen who act as voluntary bailiffs. Evidence of a kill has to be produced in the form of samples of the dead fish and of the water which are officially sealed after being taken. The samples are then forwarded to the laboratory of the Local River Institute or the State Veterinary Institute for analysis. The results of the analysis are used by the official assessor who gives an opinion as to the extent and value of the damage caused. The Fisheries' Union can make a claim for compensation based on this opinion to the Commercial Court. The Fishermens' Associations are relatively successful in obtaining compensation although this may take some time.
Technical adjustments
In the past a considerable amount of damage was caused by adjustments to the river course especially in the case of trout streams and submontane rivers. The straightening of channels, elimination of meanders and mining of the riverbed has resulted in a decrease in the length of rivers and in a decline in productivity. These actions have been brought to a halt and river managers concentrate more on channel maintenance through removal of sediments and bank stabilization. There remains a serious threat in that the remaining pristine rivers such as the Hron, Orava and Poprad may be impounded.
There have been several attempts at river rehabilitation. In one such example, the River Impel, dams have been built to raise water levels upstream to a point where they flood the backwaters. In other areas bio corridors are being built round impounded reaches to allow the fish free movement up- and downstream.
Improvement and irrigation
The use of water from reservoirs for irrigation results in lowering of the water level, reduction in surface area and a decrease in overall production. Drawdown can also have a positive effect in that it encourages growth of vegetation on the exposed banks, and improves spawning as the vegetated areas are flooded with water levels rising in the spring of the following year. Extraction of water directly from the streams greatly decreases stream flow especially in the dry summer.
The former considerable fluctuations in water level of large reservoirs due to periodic needs for power generation have been reduced following the signature of an agreement between the Slovak Fisheries' Union and Local River Administrations. These agreements guarantee high water levels in spring and there have been three years of very good spawning of phytophylic species such as carp, pike and wels as a result.
Extractions for drinking water
Extraction of water directly from the water courses has caused decreases of between 30 and 50 percent in stream flow throughout the year. This has proved especially damaging to trout streams where shelter is lost, the river segments into separate reaches, water overheats and streams may even desiccate completely resulting in kills of the salmonid fish population. Over the last twenty years extraction of water directly from the headwater springs has caused damage equivalent to that caused by stream regulation.
Small hydroelectric plants
The construction of small hydroelectric plants has become fashionable in recent years or the basis of their alleged ecological purity. The arguments for the non polluting nature of such installations are clear when only water and air quality criteria are considered.
However, other effects of such generating facilities make them ecologically dangerous. Should such plants be used to maximise the hydroelectric potential of Slovakia it is highly probable that the biology and ecology of its inland waters would be destroyed. At the same time the amount of power generated would be minimal, relative to the needs of the country.
While the Slovak Fisheries' Union is not opposed to development of this kind it does advocate a rational approach to choosing the sites for installation of new dams. There should also be a careful review of the balance between economic benefit and ecological impact. Unfortunately the two factors are contradictory as the more economically viable the plant the more negative its impacts. The most significant impacts of small hydroelectric power plants are as follows:
Construction - temporary, direct impacts
Landworks associated with the construction of the reservoir destabilise the river. In particular turbidity increases with a tendency for the fish to migrate away from the affected reaches. Deoxygenated residual waters also increase the mortality of eggs of lithophilous species.
Remedial measures
Construction works have to be carried out as quickly as possible to reduce impacts to a minimum. The period for construction should be established to avoid the spawning period of the principal fish of the region.
Dam - permanent, direct and secondary impacts
A dam that extends over the full width of the river effectively halts migration up and down stream. Any barrier of more than 30 cm is an insurmountable obstacle for cyprinid species. Barriers higher than 60 cm limit salmonid migrations in proportion to flow and velocity. The rise in level upstream of the dam creates a lake. Small hydroelectric dams are generally constructed in the steepest reaches of the river for economic reasons. in most cases this leads to permanent damage as the rapids, which are the most valuable centres of for spawning and production, become submerged. The submontane reaches of Slovakia's second category rivers, (Vah, Hron, Poprad, Dunajec) and third category rivers (Orava and Turiec) are typically high quality huchen biotopes.
Remedial measures
The total height of any dam should not exceed 2.5 m. A fish pass should be built into all dams in trout rivers that are higher than 60 cm and in non-trout rivers that are higher than 30 cm.
Raised water level - permanent, secondary impacts
The decreased velocity of flow of water in an impoundment results in an increase in sedimentation in the reservoir. The original benthos characteristic of flowing waters is replaced by an impoverished benthos characteristic of lakes. The original riverine biotope is replaced by standing water to which the species are ill adapted. As a result the high-value rheophilic species disappear and are replaced by lower-value species. The naturally flowing river is characterized by a drift of small organisms and of detritus which forms the basis for the productivity of lower reaches. The temporary halt in flow causes such organisms and material to be deposited in the reservoir creating an impoverished zone downstream of the dam.
Remedial measures
The number of small hydroelectric dams on any one river should be limited in such a way that the stream retains its integrity. Generally on small dams per 10 km reach is the optimum although if the dam is low and the plant has a short derivation canal two small plants per 10 km might be acceptable.
Drainage mechanism - indirect, permanent impacts
The intake system is situated above the dam, either directly in the stream (bottom uptake), or laterally. The system, together with the inflow and outflow canals, supplies the turbines with the required water volume and subsequently discharges the water back to the stream. The length of the canals ranges from 150 to 3 500 m. Fish are swept into the turbines. A low discharge of Q 355 (Q (discharge) = volume in cubic metres per second) is kept in the old river channel downstream of the intake. The discharge is however too low to keep the river channel biologically healthy.
Remedial measures
The intake must have a fish protection device (grid) with a maximum bar spacing of 15 mm. Ideally it should have an electric protection device.
The intake canal should be as short as possible.
The bottom of the canal must be higher than the bottom of the opening in the dam.
Downstream of the intake, in the old river channel, a minimum discharge of Q 210 is biologically acceptable. One may allow also discharges of Q 270 – Q 300, but such discharges lead to a decline in the total stream productivity and to changes in the stream character.
Reduction of water flow - permanent, periodical, direct and secondary impacts
Impacts are visible above the dam and are permanent in the former river channel below the drainage outlet. A reduction in discharge to a minimum, followed by a current velocity reduction, leads to a reduction in the total water surface area and to changes in the bottom fauna. The absence of floods may lead to sedimentation of the river channel.
Remedial measures
One can periodically wash out the accumulated sediments with an artifical water release, thus simulating a flood wave.
Machines and equipment - permanent direct impacts
The impact of various types of turbines on the fish fauna is quite different. Some types of turbine are particularly dangerous in that they suck in and destroy aquatic organisms.
Remedial measures
To ban the use of electric turbines of the “Bak” type which are particularly destructive.
Biocorridors - permanent, periodical, direct and secondary impacts
Biocorridors are installed primarily to aid migrations round the dam and reservoir. In addition to the need for fish to move between feeding and breeding grounds migrations are essential in maintaining self-regulatory mechanisms in the populations. One such function is to maintain the genetic diversity of the genetic base of the wild fish stock. Migratory fish species usually require lengths of unencumbered river in excess of 100 km to complete their migrations (barbel, nase, grayling and huchen). Dams break the river into smaller segments isolating fish populations from one another. If the inter-dam reaches are too small the fish lose their ability to reproduce. Even if reproduction occurs this takes place within a diminished gene pool with an eventual risk of a decline in genetic fitness.
Remedial measures
Construction of biocorridors to permit migration around dams
Prospects for further development
The evolution of recreational fisheries in Slovakia reflects the current changes in society. During the last decade there has been a continuous increase in the number of members of the Fisheries' Union, in the number of fish stocked, in catch and in the surface area of waters utilized. There has also been a change in the structure of the fish fauna in favour of economically valuable species. The recreational fishery was accessible to everyone and was based solely on his interest not his financial situation. The Slovak Fisheries' alliance participated in research programmes on aquatic ecosystems in collaboration with universities, research institutes and professional organizations. Recreational fisheries have developed beyond the status of mere hobby into a serious institution protecting the ecology of running waters of Slovakia.
Further development of running waters depends on the new Waters Act and on amendments to the Fishery Act and, eventually, to a complete revision of the Act. Should Act 102/63 coll. be amended, Slovak fisheries may maintain its trend towards democratic management of the fishery and its role as protector of the waters. However, should a new Fishery Act be enacted the sector will be subjected to widescale privatization and increasing control of fishing rights by the private sector. Fishing grounds may be split between numerous tenants and the overall supervision of the sector assigned to the State. While it is impossible to judge how effective this will be for the protection of the resource it would appear that the fishery will no longer be as accessible to all social classes. The restriction of recreational fisheries to certain classes of person would result in a change in expectations from the fishery which could in turn influence management policy regarding introduction of new species and stocking of existing ones.
