A boost for endangered mussels

A SURE sign of a healthy river is the presence of the freshwater mussel which has largely disappeared in Ireland in recent decades.

The reasons for its demise are obvious – the species survives only in pristine water.

Believed to be one of our longest living animals, with a lifespan of up to 120 years, it was once widespread, but is now found in very few catchments. Ireland is estimated to hold around 46% of Europe’s freshwater mussel population, with the Munster Blackwater catchment said to have a large part of the national population.

The future prospects of the endangered species have been given a welcome boost by scientists from Queen’s University Belfast, following a 12-year cultivation project. Over 300 of the mussels, which are threatened in many parts of Europe and North America, have been released back into the wild at a range of secret locations in Northern Ireland.

Importantly, the Queen’s conservation scientists will be able to keep tabs on the mussels after attaching tags to the outside of their shells. The passive integrated transponders, or PIT tags, can be located by a receiver much like a metal detector.

In that way the researchers can then locate the animals in the riverbed and monitor each mussel’s progress.

Since 1998, Queen’s scientists have been working alongside experts at Ballinderry Fish Hatchery, in Co Tyrone, in the cultivation of these precious but very slow growing mussels which can reach 17cm in length.

In Northern Ireland they are currently teetering on the brink of extinction and the only counties in which mussels currently exist are Tyrone and Fermanagh, according to Conor Wilson, a PhD student at Quercus, Queen’s research centre for biodiversity and conservation science.

“Freshwater mussels are an important part of the ecosystem in many rivers as they filter water keeping it clean and clear. This improves the environment for other plants and animals, and ultimately, humans,” he said.

“Our hope is that eventually, through a programme of breeding and tracking, we will be able to see the equilibrium restored in these rivers and bring the levels of mussels back to what they were 100 years ago, before they were affected by a variety of factors including overfishing and habitat degradation.”

The year-long release programme of the mussels has just been completed and those involved say it has been a big success. Dr Dai Roberts, academic leader on the project, believes it will ultimately show whether captive breeding and release is a successful method of halting the decline of severely depleted populations.

Freshwater mussels are listed by the International Union for Conservation of Nature as globally endangered. They have undergone a substantial population decline over the last century due to habitat loss, pollution, pearl fishing, river engineering and siltation.

Their life cycle involves mussels releasing larvae into the water. The larvae need to attach to fish gills, usually salmon or trout, for a period of about six months before falling on to the river bed to settle and grow into young mussels.

They burrow into sandy substrates, often between bolders and pebbles, in fast-flowing rivers and streams, and require cool, well-oxygenated and soft water which is free of pollution. In a detailed submission to the Department of the Environment, An Taisce outlined its concerns and threats to the freshwater mussel from forestry and farming operations, saying it was essential the forest service complied fully with the EU Habitats Directive.

“In doing so, the forest service must ensure that no damage occurs to the habitats and populations of freshwater mussels through granting of licences for afforestation, felling licences and forest road approvals,” said Anja Murray, An Taisce’ natural environment officer.

“It is with these licences that the forest service approves species mixes, use of pesticides and fertilisers, lays conditions for sediment traps and buffer zones, and approves planting regimes which dictate future management options.” She also said use of chemicals in farming posed huge risks, warning that one accidental spill, or careless discharge, could obliterate a mussel population. There was a need for further investigation into the use and regulation of chemical products, she felt.

Furthermore, exemptions to the Nitrates Directive in sensitive areas were ‘not compatible’ with mussel conservation. An Taisce also highlighted problems caused by discharges to watercourses from septic tanks that were not working properly. This was a serious issue, Ms Murray said, but it was not being addressed.

However, a carrot suggested by Ms Murray was that landowners be financially rewarded, through a subsidised support scheme, for helping with mussel conservation.

Such a scheme would include work to stop silt from getting into rivers, buffer zones for silt and nutrients, and farming without toxins.