Monday, 01 May 2017 00:00

Breeding salmon and sea trout for restocking

Fishermen have been catching salmon and sea trout for years in Lithuanian rivers such as the Nemunas and its tributaries. However, a significant decrease in the population of these fish in Lithuanian waters has been observed since the fifties. Intense fishing pressure, pollution, and poaching were the main causes for the dramatic decline in salmonid numbers. Natural resources were also considered a legitimate source of food, an attitude that was widespread during that period and not only in the Soviet region.

At the hatchery eggs are hatched and the fry grown to 1-2 g before they are released in to rivers.

Since 1991, when Lithuania regained its independency, the scientific community and administrative authorities have drawn attention to the status of fish and shellfish stocks in the country’s water bodies. Discussions about artificial salmon breeding were initiated. Latvia’s success in using artificially bred salmon to boost the catch of Baltic fishermen also contributed to the enthusiasm. The work intensified when Lithuania joined the European Economic Area and started participating in the activities of the IBSFC (International Baltic Sea Fishery Commission) and its Salmon Action Plan 1997-2010. This provided the basis for a national programme for the recovery and protection of salmon resources including artificial breeding measures.

 

Recirculation systems introduced with Danish assistance

The first activities started at the Žeimena fish farm, named after the adjacent river, a natural spawning ground for salmon and sea trout. Rainbow trout have been bred at this facility since 1965 so all the infrastructure necessary for salmon breeding existed. However, a new salmon and sea trout breeding plant based on recirculation was established in cooperation with the Danish government. The first plant was equipped with an incubator with growing tanks for juveniles built in 1998. The next year the first salmon juveniles were released into rivers. Over the years, production capacity has been expanded and today the Žeimena subdivision of the Division of Pisciculture controlled by the Fisheries Service under the Ministry of Agriculture operates three independent closed water systems breeding salmon, sea trout, and grayling.

At Žeimena the focus is exclusively on the recovery and strengthening of natural resources. Salmon and sea trout are bred only using broodstock from the wild, which are returned to the natural environment after taking roe and milt. On average, 80 percent of the salmon and sea trout grown in the hatcheries are released at 1-2 g of body weight. This enables the fish to adapt better to natural conditions and promotes the development of the homing instinct. The rest is released as 1 year smolts. In recirculation systems salmon smolts can grow from 30 g to more than 100 g in one year. The number of juvenile salmon released annually during each of the last eight years amounts to about 150 thousand parr and 25 thousand smolts. The figures for sea trout are slightly higher reaching on average 170 thousand parr and 30 thousand smolts annually.

Broodstock for the breeding activities are taken from the wild, stripped of eggs and milt, and returned to their natural habitat.

Breeding and releasing fish has helped threatened salmonid populations

Studies of salmon and sea trout abundance in Lithuanian rivers conducted by Nature Research Centre and Fisheries Service specialists since 2008 show significant growth in resources (Fig. 1 and 2). From 2000 till 2016, production of wild smolts increased from 6,000 to more than 35,000 on average. Proportionately, more of this fish was released into rivers annually. The variation in abundance of wild populations is mostly determined by weather conditions, while variation in production is mostly dependent on the number of caught wild salmon and sea trout broodstock. Preliminary data from 2016 show that the growth trend will be maintained also in the nearest future. Artificial breeding has helped to recover and strengthen salmon and sea trout populations in most of the Lithuanian salmon rivers not only by the direct augmentation of the existing salmon stock, but also indirectly – by reducing pressure from fishery on wild salmon in mixed stocks fisheries in the Baltic Sea.

Artificial breeding was not the only measure that helped salmonid fish populations to recover. The integral approach has also influenced other decisions. Each year, in cooperation with the Ministries of Agriculture, Environment, and National Defence, the Fisheries Service organises initiatives to protect salmon and sea trout spawning sites; punishments for poaching and fishery rule violation have been made much stricter; and certain river works have been stopped. The Fisheries Service has also successfully implemented several fish passage construction projects on river dams. These works have resulted in sea trout being deleted from the Lithuanian endangered-species list, and in 2011 salmon was transferred to the category for restored species.

 

Recreational fishermen are part of the populations rehabilitation efforts too

The increase in salmonids has allowed recreational fishing rules to be simplified. In recent years, salmon and sea trout have become the most desirable target for non-commercial fishermen in Lithuanian rivers and the Baltic foreshore. Salmon and sea trout may be caught in the Baltic Sea by anyone, and in interior water bodies by recreational fishermen with a permit to catch these specific species. Sea trout caught in the sea should have a minimum size of 60 cm and in interior water bodies of 65 cm. Both in the sea and in freshwater only one salmon or sea trout may be taken by a single fisherman during a single fishery. Despite these restrictions catches by non-professionals have already surpassed those from commercial fishing. Recreational fishermen, by fishing salmon and sea trout, contribute to funding breeding work and other environmental projects.

The Fisheries Service will continue its breeding activities to manage salmonid populations. Although strengthening and increasing most salmon populations has been successful, the initial target – to increase wild smolt production to 50 percent of the potential capacity of a river – has still not been reached in many rivers. In the future, the regular tagging of released fish is planned and new fish passage construction and other projects will also be implemented.