Tus­sles for mus­sels: a species un­der threat in the Doo Lough val­ley

The Irish Times - Weekend Review - - OUTDOORS - Michael Viney

Across the moun­tain, the wilder road to Gal­way twists through the bogs of Doo Lough Pass, skims the shores of two dark lakes and swerves through the old stone bridge that spans the Bun­dor­ragha river.

On its short, swift run down to the fiord of Kil­lary har­bour, the river is an idyl­lic salmon stream, with riffs and rock weirs and deep, swirling pools. In sum­mer rains, up­mar­ket an­glers in wet-weather gear cast bliss­fully across the spate.

Along with the pas­sage of salmon and sea trout to the lakes be­low Del­phi Lodge, the beds of Bun­dor­ragha’s pools are home to some of the largest and health­i­est colonies of the fresh­wa­ter pearl mus­sel, Mar­gar­i­tifera, in Ire­land.

Fewer than 30 of our rivers now pos­sess this beau­ti­ful mol­lusc, its black shells lined with gleam­ing nacre, vi­o­let and blue. And only a hand­ful are breed­ing young to sup­port this in­ver­te­brate’s re­mark­able life­span of a cen­tury and more, scant­ily nour­ished on a flow of or­ganic par­ti­cles.

Equally re­mark­ably, the mus­sel’s in­fant sur­vival de­pends on pre­pos­ter­ous odds.

In early au­tumn the fe­male mus­sels re­lease clouds of lar­vae called glochidia. Whirling down­stream on the way to the sea, each mi­cro­scopic larva has a mat­ter of hours in which to be breathed into the gills of a swim­ming salmon or trout.

Of some 10 mil­lion lar­vae per mus­sel, per­haps 40 find a host. Of those, per­haps two will hang on long enough (a cou­ple of weeks), ab­sorb­ing food from the gill tis­sue, to grow into vi­able but still minute shelled mus­sels.

They then fall off the fish and bur­row into sand or gravel, where they live for some five years, feed­ing on bac­te­ria. It takes this long for them to grow enough to with­stand the tug of wa­ter in flash floods and the shift­ing of stones at the sur­face of the river bed. For this they need a flow of well-oxy­genated wa­ter, free of smoth­er­ing silt.

Pearl trade

The chief his­tor­i­cal threat to the mus­sels was trade in their pearls though only per­haps one in 100, in­vaded by a par­a­sitic fluke, seals it in lay­ers of nacre. Huge num­bers of mus­sels were sac­ri­ficed for a sin­gle saleable pearl, a pil­lage long out­lawed in both is­lands but still rarely at­tempted.

Lo­ca­tions of the mus­sel rivers were once a semi-of­fi­cial se­cret. But the trade has faded and its tran­sient dam­age has been over­taken by modern fer­tiliser pol­lu­tion and the flow of silt from up­land forestry and over­grazed hill­sides. Re­search, ru­ral aware­ness and pro­tec­tion of the species are the new pri­or­i­ties.

Nine­teen river catch­ments with the mus­sel have long been des­ig­nated Spe­cial Ar­eas of Con­ser­va­tion by the Na­tional Parks and Wildlife Ser­vice. But progress into ac­tual man­age­ment plans has been slow – a fail­ure that this month brought threat of court ac­tion from the Euro­pean Com­mis­sion.

Such threats are now quite fa­mil­iar to Ire­land and many other coun­tries slow to ful­fil the EU na­ture di­rec­tives. The con­trols avail­able to Ir­ish con­ser­va­tion have also had to deal with con­sti­tu­tional pro­tec­tion of prop­erty rights and its im­pact on law and reg­u­la­tion.

More ac­tive so­lu­tions have now been sought in agri-en­vi­ron­men­tal schemes that em­body lo­cal lead­er­ship and are backed by pay­ments for eco­log­i­cal re­sults. Among them is the multi-agency Pearl Mus­sel Pro­ject, which has been run­ning for five years with a bud­get of ¤10 mil­lion.

Pri­or­ity ar­eas

If it suc­ceeds, lo­cal farm­ers, re­searchers and ad­vis­ers will col­lab­o­rate to se­cure the mus­sels’ fu­ture in eight pri­or­ity catch­ment ar­eas in the west of Ire­land. Bun­dor­ragha is among the first con­sul­ta­tion meet­ings, and some 140 ac­tive sheep farm­ers are be­ing asked to meet with the Pearl Mus­sel Pro­ject team at Glen Keen Farm on De­cem­ber 4th.

The long val­ley be­tween Mweel­rea and the She­ef­frys has some of the high­est rain­fall in Ire­land, with sil­very hillside cas­cades in ev­ery heavy down­pour. While the lakes that feed the river can seem no­tably clear to an­glers, the deeper flow of peat silt is a long-term haz­ard to Mar­gar­i­tifera.

‘‘ The chief his­tor­i­cal threat to the mus­sels was trade in their pearls though only per­haps one in 100, in­vaded by a par­a­sitic fluke, seals it in lay­ers of nacre

These moun­tains were once se­verely over­grazed, but noth­ing in the new pro­ject pro­poses fur­ther lim­its to flocks. Its ob­ject is “main­tain­ing nat­u­ral habi­tats” and “farm­ers will be af­forded flex­i­bil­ity to man­age their lands in a way that achieves the best en­vi­ron­men­tal re­sult” (pearl­mus­sel­pro­ject.ie/farm-scheme).

One small new mea­sure is be­ing trialled in Co Kerry, where the sep­a­rate Ker­ryLife Pro­ject, part-funded by the EU, works with farm­ers in the Caragh and Black­wa­ter catch­ments. Fab­ric fences that let wa­ter through but hold back silt are meant to re­duce run-off from farm roads and tracks into the rivers.

In the Doo Lough val­ley, how­ever, nat­u­ral forces are at their fiercest, and cli­mate change al­ready brings stronger storms and heav­ier rain to tear at moun­tain­sides and bogs. The val­ley’s farm­ers are a hardy, re­source­ful lot. If it’s worth their while, they’ll think of things to do – or not, as the case may be.

Fewer than 30 of our rivers now pos­sess this mol­lusc. IL­LUS­TRA­TION: MICHAEL VINEY

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