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Migration of Atlantic salmon in The Tuloma River

Migration of Atlantic salmon in The Tuloma River

The Atlantic salmon (Salmo salar L.) – it is a valuable fish and is fished industrially, as well as favourite for recreational and sports fishing. In the Kola Peninsula the salmon’s presence is conformed in 79 rivers (in 43 Barents Sea rivers and 36 White Sea rivers), of global significance. Six of the major rivers have dams built on them, therefore, the growth of salmon in those rivers is completely or partially lost. The River Tuloma is one of the latter.

In this article we have used the statistical data of passage of salmon through the fish gates of the Lower-Tuloma HEP (data by FSUE “PINRO” and FSI “MURMANRYBVOD”), including the data collected in 2010 at the Lower-Tuloma fish gates.

The Tuloma River is one of the largest river systems of the Kola Peninsula; its waters cover an area of 18231.5km². due to the construction of two hydroelectric plants (Lower-Tuloma in 1943-36 and Upper-Tuloma in 1963-65) all the spawning and breeding areas of salmon, which were in the main channel starting from the source, have been flooded and became unsuitable for spawning. Starting from 1937 the salmon is let through the lower channel of the river through ladder-type fish gate (a system of canals and wells of ladder-type, imitating the rapids. Total length is 450m. It has 65 steps with a descent of 0.3 m every step. Total descent is 19m). The passage of salmon to the upper reaches of the Tuloma River was stopped in 1963-65 due to the construction of the Upper-Tuloma HEP. Since 1965 the underground fish gate from the Borland sluice started. In 1970 the passage of breeders was totally stopped due to inefficiency of fish passage. Due to this currently the salmon breeds only in the tributaries, which fall into the Lower-Tuloma reservoir.

However, even after the construction of the HEP, which caused the reduction in breeding grounds, the flock of Atlantic salmon in River Tuloma is still one of the largest in the Barents Sea shores of Kola Peninsula. So, even after the construction of the Upper-Tuloma HEP, its accounted population during active passage reached 12.8 (1074) and 11.6 (1990) thousand pcs.

The seasonal changes in spawning migration of salmon in the Tuloma River had the following specifics, before regulation:

The breeding migration of summer and early-run salmon started in the river from August and continued till September next year, with a gap from December to April;

The breeding migratory flocks included various biological species, which differed from each other by relatively permanent periods of migration, marine lifespan, size, adulthood, relative numbers, gender ratio and other indicators (morphometric characteristics, fat content);

The salmon was found all over the waters of the River Tuloma including the upper reaches of rivers Nota, Lotta and other tributaries from the Nota Lake;

The intensity of migration and the spread over the river directly depended on the water conditions, mainly on the level of water in the river;

The changes were characteristic to have a few peaks, reflecting, mainly, the change of various biological species, as well as the beginning of favourable water conditions.

After the construction of the Lower-Tuloma HEP, the spawning migration underwent significant changes. Since the dam is near the head of the river, the entrance of breeders into the river was limited by the periods of functioning of the fish gates, which remained open from the end of May or beginning of June till the beginning of October. Despite the fact that the fish gate was scheduled in synch with massive arrival of spring salmon, its migration was obstructed because of long waiting periods on the other side of the dam. It turned out that due to the deceptive currents from the bypass canal of the turbine and spillway, the salmon had a tough time finding the fish gate.

The passage through the fish gate takes on average from 2 to 10 days.

Before entering the river the migrating fish gather some 55-80 m away from the dam, where the current weakens, whereas the entrance to the fish gate is located at a distance of 53 m from the dam. This makes it difficult for the fish to enter the fish gate. Apart from that, the structure of the fish gate had certain deficiencies, which affect its efficiency. Following are the main shortcomings:

1. The entrance to the fish gate is located in the area of strong currents from the 4 ^th aggregate, above the front of mass distribution of fish;
2. The stream from the fish gate is unnoticeable for the fish, because when the 4 ^th turbine is functional, the stream (channel) is directed aside, opposite to the main current, which slows it down at a distance of one to a few meters from the entrance;
3. During total high tide the attracting effect of the stream decreases. As a consequence the fish gate attracts the fish only 57% of times du ring the high and low waters, when the level of water – 50-210 cm above zero;
4. The speed of dislocation of fish through the fish gate is from 70 to 230 m/day, which is equal to the least speed under natural conditions. At such speeds the salmon takes a few days to pass through the fish gate.

Some parts of the fish gate are too tough to pass. For example, direct observations showed that the first 7 steps into the fish gate were crossed in first attempt only by 27% of the fish.

Due to this hold-up beyond the dam the sequence of spawning migration undergoes changes. First of all this can be seen from the time of entrance of “spring” and “summer” forms into the river, the main part of which goes up the trap of the fish gate in the end of June or mid of July.

The average number of fish that passed through the fish gate from 1936 to 2007 was 6500 pcs/annum. The peaks of population (more than 10000 fish/season) was noted in 1960, 1961, 1962, 1974, 1975, 1984, 1990 and 2006 (figure 2).

Figure 2: Graph of salmon population, calculated at the fish gate of the Lower Tuloma HEP.

The data regarding the population of salmon in the Tuloma basin before the regulatory sanctions is very approximate and referential in nature, because the fish was drawn all over the Kola Peninsula and in the lower and middle streams of the river by many Lapps, colonists and other people.

As per the modern concept of development of fisheries based on the cautious approach, the flock of salmon in the River Tuloma can be called an important recreation resource. However, the fish management system in this region is unable to use the full potential of this water body. The salmon population can be developed in the River Tuloma by implementing a host of measures, including the effective protection of fish and their migration pathways, reclamation measures to let through and protect the fish, especially by modernizing the Lower-Tuloma fish gate to make it more effective and passable, as well as the reinstatement of the Upper-Tuloma fish gate or construction of a new one and redevelopment of the spawning areas of salmon in the Upper-Tuloma HEP area.