RESIDENTS AND GUESTS. FISH AND LAMPREYS.
Rivers are important habitats for many species of animals, but especially for the species, including fish and lampreys, which spend their entire life in water. Some of them move short distances, others take long journeys which last several years. At their life paths they have to face many challenges before wild fry grow up and reach maturity in order to produce spawn effectively and give birth to a next generation. One of the two main project’s tasks is to provide such places and access to them. The second objective is to protect and improve the ecological status of water-crowfoots rivers and the habitats of species recognized as the most valuable among the native ones. These water wanderers need to have a place to come back to.
Strzebla potokowa (Phoxinus phoxinus), a species of a small fish in the family Cyprinidae that used to inhabit in great numbers submontane and upland rivers and over a large area of Eurasia. It is observed to live at the height of up to 2 000 m.npm. The species with interesting colouration of both sexes, which changes slightly during breeding – that is from April to June. At this time the males stain more intensively and their stomach becomes red. The males and females get a spawning rash. They need shallow, gravel-sandy places for reproduction. It is present in cool, rapid streams, creeks, rivers and mountain lakes under the condition that the water represents a good ecological status. The species does not tolerate pollution, so its presence guarantees really pure water. It plays a significant role in river ecosystem, since it is a predator for larvae of insects and other small invertebrates, while it is itself the most common food for salmonids and other larger predators. Phoxinus phoxinus importance for salmonids is used by anglers, who make bait look similar to this species’ appearance and colouration. This fish should be one of flagship species of protected habitats 3260, therefore, as such, it should be fully protected.
Atlantic salmon Salmo salar, belongs to the family Salminodae, order Salmoniformes. It’s quite an old group of species, with respiratory organs less developed than in many other groups, which explains their very high requirements in terms of thermals and oxygenation of water. The one of our largest native fish inhabitants, grows up to 140 cm in length and more than twenty kilograms in weight. The extinct Drawa population was described as reaching the largest size of all populations. Specimens of 150 cm in length and more than forty kilograms in weight were recorded. Salmon is a real marathoner, wandering across the North Atlantic, from Norway, Iceland and the British Isles reaching the waters of Greenland and the Labrador Peninsula. These journeys are often several thousand kilometres long. Baltic populations travel on a smaller scale, due to the smaller area of this basin, but it is not unusual to meet fish from river basins from the north of the Gulf of Bothnia off the coast of Poland. These migrations are mainly for food – herrings and sprats – thanks to the abundance of which, the Baltic salmon’s growth is the fastest of all the Atlantic populations. A documented record cited by Professor Bartel was 19 kg in weight during three years. During this time the fish take on silver-grey, with darker back, colouration, which is characteristic of marine pelagic fish. Salmon is a two-habitat species, anadromus – adults live in saltwater, but they return to spawn in native freshwater streams. Their reproduction takes place in autumn, in rapidly flowing, gravelly bottom, medium-sized rivers and larger streams. Adult fish called spawners, significantly different in colour, for this reason called ‘colourful’ fish, migrate to spawn in the upper sections of rivers. Males, in other languages often called ‘cock ‘, change not only their colour but also appearance. The lower jaw bends and forms a characteristic muzzle. The historic spawning grounds of this species are found in mountain and submontane tributaries of the rivers Vistula and Odra, to where they trekked for several months. Today most of these basins are not available for fish due to crosswise installations and large transformations of morphology made over the last two centuries by man. Thus, at the present time it is very important to maintain and repair the ecological state of the river basins, to which they still manage to reach. These are mainly Pomeranian upland rivers, both in the Vistula basin – Drwęca, and the Odra, where the Drawa plays the leading role. Apart from them, only small parts of few rivers directly flowing into the Baltic Sea are at the fish’s disposal – the Łeba, Słupia, Wieprza, Parsęta with Radew, Rega, Gowienica and Ina.
For natural reproduction they need clean waters with a rapid current and appropriate bed in order to “build” a spawning nest, in which fertilized eggs will be placed. A mound, the main part of the nest, is built by females, which use the strength of the current to create a powerful downdraught of water with her tail near the gravel to excavate a depression. After she and a male fish have eggs and milt (sperm), respectively, upstream of the depression, the female again uses her tail, this time to shift gravel to cover the eggs and milt which have lodged in the depression. It depends on the gravel’s structure what part of the eggs will be in the “mound” and what will be washed off the mound, where it will become food for other fish, including individuals of their own species. Some of the eggs situated in the spaces between the gravel and stones, rinsed with well-oxygenated water for about four months, lies and transforms into larvae, which hatch in the spring, usually in March. What part of the spawn will become larvae, depends on many factors that make up the ecological status of the parent flow. A very important factor for the eggs’ survival is the energy condition of the flow, including the amount of deposited slurry, but also the amount and fluctuations of waters, quality and flow of groundwater from the so-called. hyporheic zone in a valley, and the content of substances which affect the oxygen’s content. Research shows that the morphological condition of a river bed and valley is of great importance. The more a flow and basin are closer to a natural one, the higher the survival rate. In order to survive till larvae of other fish and insects develop (which are food) the larvae of salmonidae have a large yolk sac, where nutrients for the first weeks of their life are accumulated. By consuming gradually the supplies from the sac, the larvae become fry, which begin to swim actively and take food after having fully digested the contents of the yolk sac. In the early days it is essential for the fry to have access to so-called starter food, including microscopic larvae of other fish, in our conditions mainly burbot’s. In good conditions, the fry grow rapidly and become fry called paar, gradually settling slightly deeper parts of sections, in which they came into the world. In the second year, sometimes in the third, after having reached several centimetres in length, the fish begin a passive, carried by the current, trekking down rivers to the sea; on their way they undergo a process of physiological changes that allows them to survive a shift from freshwater to saltwater. At this point the salmon are called smolt – they lose their river, similar to trout’s, multicoloured coloration to become small, silver fish which reach the sea. This is the first great physiological stress, because these freshwater fish become residents of a completely different, saltwater environment. The juvenile period, in our climatic conditions, usually lasts two years. Adults live for a few years in salt waters, and once ready for reproduction, thanks to the phenomenon called homing, they return to the same freshwater tributary they departed from as smolts. This is the second great stress in their lives, because from salt waters they enter the sweet ones again. After entering the estuaries sections the fish rest for some time, adjusting to freshwater World again. Then they move upward, toward the spawning grounds; On their way they have to overcome numerous obstacles, including artificial ones which are the most difficult. They also try to avoid many traps, from predators, to the man – poacher. Observations and experiences of groups dealing with protecting a spawning run, indicate that spawning grounds are reached by a small part of a herd, especially when protection is weak. Poaching, next to the condition of the environment, is the main factor determining a level of breeding success for this species, similarly to the sea trout and other migratory species. The environmental conditions required by the salmon are identical to those of the protected habitat of water-crowfoots rivers, hence protecting them, we protect the salmon.
The European bullhead Cottus gobio, a fish member of the family Cottidae, order Scorpaeniformes. This species as one of few of this order inhabits freshwaters. It achieves small size, usually up to 15 cm, maximum recorded specimen of 19 cm in length. It exists at the bottom of clean, well-oxygenated flows of a mountain nature. An important element of its habitat are rocky and gravel sections. The bullheads’ diet is dominated by bottom-dwelling invertebrates. It is not true that this fish is a ‘spawn-eater’ which destroys eggs of other species. The bullhead itself is an important component of larger salmonidae specimen’s diet, especially for sedentary forms of sea trout – brown trout. The fish swims with characteristic jumps.
Bullheads have an interesting reproduction, which takes place at the end of March and in April. The male finds a pit, often underneath a bigger stone, which is cleaned either by the female or the male (according to different researchers). Then the eggs are laid and guarded by the male guards, who fans them to ensure that they receive enough oxygen.
The bullhead, similar to its more ‘mountain’ poecilopus cousin, is a species extremely sensitive to the deterioration of the environment, so in many countries it is considered an indicator species of waters’ ecological quality. In order to maintain the population it is extremely important to maintain the flows’ beds in their natural form, with a great variety of microhabitats and without crosswise installations, which even in a form of a small, between ten and twenty centimetres thresholds, constitutes a serious obstacle to seasonal migration. The species does not move long distances, hence decolonisation of sections from which it disappeared takes a long time, after improvement of ecological conditions.