PROJECT DESCRIPTION
BACKGROUND
Allis shad (Alosa alosa) is a herring-like fish species which lives in saltwater, but migrates up European rivers to breed in freshwater. Historically, the eastern Atlantic and North Sea were densely populated with the fish. Only 150 years ago, several hundred thousand Allis shads were caught annually in the Rhine system and they were an important economic factor for the local population.
However, the distribution range of the Allis shad has decreased dramatically and it is now listed as priority species in Annex II and V of the Habitats Directive. The main causes of this dramatic decline were over-fishing, increasing river pollution, destruction of spawning grounds and the construction of river obstacles such as dams and weirs.
Significant efforts had already been made to improve the Rhine for migrating fish. Environmental legislation had served to alleviate pollution and a North-Rhine Westphalia (NRW) migratory fish programme had focused on overcoming river barriers, for example by constructing fish ladders across weirs. This had shown improved access to spawning grounds for migratory fish such as salmon and North Sea houting. However the Allis shad had not returned and was still considered extinct in the Rhine and in most Atlantic tributaries.
OBJECTIVES
The overall objective of the highly ambitious LIFE Maifisch project was the conservation and protection of Allis shad in Europe through re-introduction to the Rhine system. Through the reintroduction of larvae, the project aimed to achieve a self-sustaining population that would return to the same river to breed in the future without the need for ongoing restocking activities.
It aimed to develop a breeding programme in South-West France, where the fish is still found naturally. It then planned to transport the larvae and restock the Rhine and its tributaries in Germany.
The project sought to meet the following significant challenges:
RESULTS
The Maifisch project was a tremendous success. It managed to optimise all major steps in the rearing process of Allis shad larvae and to achieve the release of 4.8 million Allis shad larvae into the river Rhine in Germany.
The project worked with an American expert with experience of a reintroduction programme for the American shad (Alosa sapidissima) to increase understanding of the optimal processes for release of the larvae. They examined passage conditions and mapped the suitability of spawning sites for the fish along the Rhine river system. Laboratory experiments assessed the effect of aspects such as different substrate types and waves from shipping on the hatching, survival and behaviour of larvae. This led to a first reintroduction management plan for the Rhine system.
Over the three breeding seasons covered by the project - 2008-10 - the project team caught a total of 644 spawning Allis shad through fish lifts at two sites on the Garonne and Dordogne rivers in South-West France. With private fish farmers, the project then tested breeding and rearing procedures. The shad were treated with hormones to speed up spawning and the fertilised eggs kept in breeding tanks. The emerging fry swam into hatchery tanks where they were fed with Artemia, which were also reared in tanks.
The project developed considerable learning around caring for eggs, optimal water conditions and prevention of infections. The survival rate of eggs to the end of the rearing process increased from 28% in 2008 to 65% in 2010. It also optimised processes of treating the adults with hormones by injecting through plastic bags and the marking of larvae with pigment to enable tracking and monitoring after release.
The first restocking of the Rhine occurred in June 2008 and was repeated and expanded in the following two years. Much was learnt around optimal conditions and processes for release including the benefits of acclimatisation and additional feeding in basins in the river, releasing at night to avoid predation, optimal transport bags and conditions, and the best age at which to transport larvae.
The success of the project was notably shown when 30 juvenile Allis shad were caught in the lower Rhine near the German/Dutch border in autumn 2011. These were the first juveniles to be caught there for more than 50 years and showed they were successfully migrating downstream. Their marking revealed they had been released by the project and their size showed them to be developing healthily and appropriately at age 4-5 months.
The project produced various guidance documents which set out much of the learning around rearing and reintroduction of Allis shad which was not known before the start of the project. The project has been followed up by another LIFE project (LIFE09 NAT/D/0008) which aims to establish a fish farm in Germany and to monitor whether mature Allis shad are starting to migrate back to the Rhine system as hoped.
Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).
