RRC Visit to Cynrig Hatchery

Ann Skinner, RRC Board of Directors

9 lucky participants were treated to a tour of the fascinating work carried out by Natural Resources Wales (NRW) staff at Cynrig hatchery near Brecon in Wales. Initially developed to raise salmon, sea and brown trout for restocking after pollution incidents, the hatchery was taken over by NRW and gained a Home Office Licence in 2013. It is now the only facility in Wales actively carrying out captive breeding for a number of critically endangered species: Arctic char, white-clawed crayfish, water voles and freshwater pearl mussel (FWPM). All are protected under section 7 of the Environment (Wales) Act 2016, but without intervention it is likely that FWPM in particular will go extinct.

The freshwater pearl mussel is an exceptionally long-lived (over 100 years) filter feeder with a complex lifecycle that includes a period of dependency on young salmon and sea trout, when the young (glochidia) get shelter and hyper-oxygenated water by living on the gills of the fish, with no adverse effects to the host. Still present in several Welsh rivers, the mussel is considered to be functionally extinct as almost all remaining individuals are old and likely to die within 25 years – current estimates are that 50% of the population is lost every decade. The reasons for the lack of successful juvenile recruitment over the last 50-70 years are manifold and include past river engineering and illegal pearl fishing; agricultural diffuse pollution leading to siltation (too much soil in rivers) and eutrophication; and declines in recruitment in their host fish species (due to climate change – floods, drought and elevated water temperatures, marine by-catch, diffuse pollution). Most mature individuals probably still contain traces of banned substances like DDT and lindane.

Adult mussels

The breeding programme starts with collection of at least 50 adult broodstock from a good population, to ensure genetic variation. The females spat in early August and up to 4000 glochidia per fish are encysted on the gills of young salmon and sea trout until June the following year.

Hatchery staff get the best subsequent juvenile survival rates using sterilised bog sediment in sandwich boxes and feeding with commercial shellfish food. Scientists in Norway have reported the best populations in rivers where there are peat bogs in the upper catchment.

The glochidia (around 300 microns) crawl around in the sediment and grow rapidly, providing there are no predators such as flat worms. Results have been extremely encouraging, with reliable survival of 40-70% of juveniles up to 3 years of age.

Filtering bog water!

 Young glochidia in petri dishes

They become filter feeders when they reach 3mm in size, and are fairly hardy when they reach 4-5mm. Most captive breeding programmes (in Czech Republic, Ireland, Norway) reintroduce the mussels to rivers at 10 years old - they can be tagged at this size so that surveys can record survival rates. Juvenile mussels are so tiny that they cannot be seen in a river bed until they are at least 10-15 years old. They require really clean gravels, with large boulders for shelter against flood events, if they are to survive in the wild.

Monitoring FWPM populations

White-clawed crayfish: berried females are captured but removed once the young have emerged, to prevent predation. The juveniles are fed brine shrimps, and the hatchery gets very good (70%) survival rates. 7,000 have been released to date into ark sites, water bodies that are divorced from the river system where there is a chance that they might remain free from American signal crayfish.

Pictured Juvenile white-clawed crayfish

Water voles: populations have experienced a 90% reduction over the last 30 years, mainly due to habitat loss and predation by mink. Water vole females breed from March to September and can have up to 6 young in each litter. The key to successful reintroduction is habitat restoration and mink trapping (remote alarms reduce the need to check traps) – mink are still present on many Welsh rivers, but in lower numbers. Releases tend to be into nature reserves and SSSIs.

Pictured Female water vole

Artic char: this rare fish is threatened primarily by eutrophication and algal blooms, but also climate change and hydro schemes (which cause river water temperature rise). The breeding programme has been particularly successful. Eggs and sperm are collected, and between 5-7000 fin-clipped individuals are released into suitable habitats each year, with a significant recorded increase in their abundance.

Pictured Juvenile Arctic char

4 Rivers for LIFE project: one of the last EU LIFE projects, with a budget of £9.1m over 5 years, covering the Teifi, Cleddau, Tywi and Usk. The focus is on river and floodplain restoration (restoring meandering channels and reconnecting floodplain meadows such as at Cors Caron), working with farmers to reduce sediment and nutrient inputs from farmland. Other elements include tackling invasive non-native species and ensuring fish passage through 12 barriers. Boulders and large woody material are being introduced to help restore natural processes. The project has ambitious targets:

  • rearing 30,000 juveniles FWPMs and releasing 1000/year (funding the upgrading of the Cynrig hatchery to achieve this);
  • 35,000 ha of land management improvements engaging 350 farmers;
  • 100 kms fencing and tree planting.
  • control of Himalayan balsam, Japanese knotweed, giant hogweed and American skunk cabbage.
  • communication and engagement work
  • monitoring of biological improvements and socio-economic impacts.

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