Ballinderry River Trust: An Effort To Save Freshwater Pearl Mussels, One of IUCN Red List Endangered Species

The Freshwater Pearl Mussel is one of the species that listed in IUCN Red List Endangered Species, this species is an aquatic bivalve mollusc in the family Margaritiferidae. Freshwater Pearl Mussel can be found on both sides of Atlantic and one of the largest surviving population is living in Northern Ireland. To maintain the existence of this species in Northern Ireland, Mark Horton with his team in Ballinderry River Trust took some ecological management action with the hope that their activities can provide survival for the species. Some of the ecological management action that has been taken including:

1. Catchment-level management

Sedimentation is a problem that interferes with the sustainability of Fresh Water Pearl Mussels (FWPM) recruitment. This can be solved by conducting catchment-level management to make it undisturbed and controlled. An example of causes sedimentation is the cattle that go down to the riverbank, making landslides and sedimentation. Some things have been done to reduce sedimentation, such as closing livestock watering point by fencing along the riverbank, makes environmentally friendly bank protection with rock revetment, and planting Christmas tree (Fig. 1). Also, cooperation with farmers, landowners, and businessmen is carried out to increase awareness of pollution that will pollute the catchment area.

2. Habitat restoration

Erosion and siltation are caused by livestock coming into the river to drink, so stabilization of the riverbank is needed to improve damaged habitats. Reconstruction is carried out in various ways, such as enclosing the entire land so that livestock cannot go to the river, planting willow trees to provide a shaded area, and placing gravel to be a clean substrate in a shallow area.

Fig. 1 Fencing and rock placement to provide riverbank protection.

3. Ex-situ conservation

A. Broodstock selection

Freshwater pearl mussel individuals are taken from the wild, then placed in captivity, which will be rotated for 10 years to increase genetic diversity.

B. Captive husbandry

Water is pumped from the river and passed into the FWPM pond. The river water will bring foods for FWPM.

C. Captive breeding

Larvae appear in July and August, then the larvae or glochidia are carried by the current and move to the fish tank that will be the host and will stay in the gills of the fish host for 1 year (Fig. 2).

Fig. 2 FWPM life cycle (Skinner et al., 2003)

D. Captive rearing

Fish that are kept and transferred to another tank for 1 year (Fig. 3). After 1 year, the mussel will release from the fish gill and live on stone beds for 3–10 years.

Fig. 3 Tank or vivarium for FWPM.

E. Population release

The population is released into the wild in two ways, hard release (placed directly at the bottom of the river) and soft release (set in a concert called “Bernhart Silo” (Fig.4)) which will protect young mussels and facilitate water flow. Juvenile mussel will be placed together with an adult mussel in place the most suitable one, such as being under a tree, has a smooth flow, and has good water quality, which has previously been done a redox examination so that it has suitable dissolved oxygen to avoid siltation.

F. Species reintroduction

Freshwater Pearl Mussel is one of the animals on the IUCN list as an endangered animal. Ballinderry river trust reintroduces this species to increase its population in the wild. The rewilding position will refer to suitable habitats such as landscaping, water quality, local riparian habitat, pearl fishing activities (Wilson and Roberts, 2011), and the abundance of fish hosts (V et al., 1994).

4. Population Monitoring and surveillance

All river areas that are reported to have a remnant of the FWMP population are surveyed using a bathyscope (Fig. 5) during zigzag transects (Young, 1991). After that, the data that obtained will be processed with GIS to get information about its spatial distribution (Reid et al., 2013). In addition, monitoring of fish hosts is also done by using electrofishing. Besides conducting surveys of mussel and host fish. Ballinderry river trust also monitoring the level of silt deposition.

Fig. 4 The Bernhart Silo

Fig. 5 Surveyor using bathyscope to survey FWPM (Horton, 2019).

The Ballinderry river trust played a major role in the Fresh Water Pearl Mussel restoration project. As an outcome, the FWMP population in 2011 was 12,947 individuals, this number increased from the previous study which amounted to 12,229 individuals (Reid et al., 2013). In 2017, Ballinderry river trust released 1500 individuals. However, the results of the survey in 2018 showed that only 60% of individuals remained, this was due to the flood disaster in August 2017 which buried or washed away the mussels. During the restoration program, the Ballinderry river then released 2500 young mussels (Horton, 2019). Ballinderry river trust also active in managing and restoring water catchment areas.

References

REID, N., KEYS, A., PRESTON, J. S., MOORKENS, E., ROBERTS, D. & WILSON, C. D. 2013. Conservation status and reproduction of the critically endangered freshwater pearl mussel (Margaritifera margaritifera) in Northern Ireland. Aquatic Conservation-Marine and Freshwater Ecosystems, 23, 571–581.

HORTON, M. (2019). Ballinderry freshwater pearl mussel restoration project.

SKINNER,A,YOUNG M &HASTIE L (2003).Ecology of the Freshwater Pearl Mussel.Conserving Natura 2000 Rivers Ecology Series №2 English Nature,Peterborough.

V, Z., ZOTIN, A., L, N. & V, T. 1994. The freshwater pearl mussels and their relationships with salmonid fish.

WILSON, C. D. & ROBERTS, D. 2011. Modelling distributional trends to inform conservation strategies for an endangered species. Diversity and Distributions, 17, 182–189.

YOUNG, M. R. 1991. Conserving the freshwater pearl mussel (Margaritifera margaritifera L.) in the British Isles and Continental europe. Aquatic Conservation: Marine and Freshwater Ecosystems, 1, 73–77.