Freshwater Pearl Mussel or Flood Defenses

With the recent horrific floods throughout the country, many have blamed supposed government’s spending cuts in flood defences as being responsible. One of the targets of criticism is the increased spending in less obviously important issues. Some believe that part of the blame, as reported in the news on the 6th of January, is the government spending on protection of the Freshwater Pearl Mussel (Margaritifera margaritifera L.)

Lynne Jones, owner of a guesthouse in Keswick and chairwoman of the Keswick Flood Action Group, said that too much attention was given to protecting wildlife and not enough on the protection of the communities.

“My sympathies to the mussels but I need my community protected”

According to David Cameron, government spend for flood defences have been increased by £2billion. Regardless people such as Mrs Jones clearly seem to believe that the money issued to protecting wildlife could be better spent. Saving wildlife seems to be of little importance, when compared to saving people’s homes from flooding. But is it?

In Cumbria almost £900,000 of funding have been issued to protect this critically endangered species by the The Environment Agency. This sounds like a lot of money, however it is a mere 0.0045% of the £2bn increases in flood defences in the entire UK. This funding will go towards research into the reasons for the species decline and how to protect the surviving Mussels in England and Wales.

However, is this as important as flood defences?

Floods can obviously be devastating for people, that much is obvious. However, they can be just as devastating, if not more so for the Freshwater Pearl Mussel (FWPM.) In February 1998, in the North of Scotland (where the only viable populations still remain), there was a flood of the River Kerry. This event massively impacted the FWPM population in the river. 50,000 mussels were killed, which is estimated to be up to as much as 8% of the total UK population. Although some populations remained unaffected by the flood, some mussel beds disappeared completely. The reason for the devastation is thought to be down to large-scale movements in the substrata in which mussels attach themselves, causing the mussels to be swept downstream.

As Climate Change is resulting in large floods in the UK to become more common. It could be said that FWPM are facing an ever increasing and possibly futile battle for survival. Threats such as criminal damage (Pearl Fishing), increasing land use, removing important habitat, altering river flows and river engineering are a serious threat to mussel populations. Combine this with environmental factors such as reduced water quality and loss of suitable habitat conditions, have led to IUCN classifying FWPM as one of the worlds most endangered species. It has been estimated that the FWPM may be totally extinct in the UK in as little as 20 years.

So which is more important, saving homes from seasonal flooding, or saving a species from becoming extinct? If you are still not convinced of the importance of protecting the FWPM (it is just a mussel right?) then maybe a greater understanding of this fascinating species might help.

The FWPM may have once been one of the most numerous species of mussel in the world. Living up to 150 years (the world’s longest living invertebrates) these large mussels, which can grow up to 15cm, begin life measuring less than 1mm. The larvae, alone with tens of millions of siblings, are ejected from the mature mussel in a mass event which occurs over just 2 or 3 days, in late summer. These larvae, known as glochidia, drift in the river current until they find a suitable host species to attached themselves to, usually juvenile salmonids. This is where the first of the FWPM’s problems occur. In recent years there have been huge reductions in water quality, which has resulted in widespread declines in the populations of potential host fish.

After a few days, the young FWPM’s attach themselves to the fish’s gills, and remain there for around a year. They then release from the fish and bury themselves into the river bed. The type of substrate the mussel finds itself is essential. Although the species is able to move slowly across the river bed to re-plant itself, it requires a specific substrate of sand or small pebbles, stabilised by boulders. If these parameters are not found, the mussel cannot survive. Water conditions are also vital as the FWPM requires silt free, well oxygenated water. With silt and sediment depositing in many rivers in the UK being widespread, the ideal habitat for FWPM is becoming less and less available.

Growing extremely slowly the FWPM feeds by filtering the water, filtering up to 50 litres per day, extracting organic particles. For this reason, it is thought that FWPM are directly beneficial to other river inhabitants, by cleaning the river water. The beds also provide a microhabitat for invertebrates on which juvenile salmonid feed. The relationship between FWPM and their host species is not fully understood although it appears to be a mutually beneficial one.

As FWPM are fragile to so many factors, requiring near pristine river conditions to survive, they are a valuable indicator of overall river health. If the population of FMPW suddenly declines in areas in which they were known to exist, it often indicates a reduction in river quality. For example, at Ennerdale water in Cumbria in 2012, there was a sudden decline of 90% of the existing FWPM population (over 90,000 individuals). An investigation to the cause was launched and it was discovered that a decrease in water level in the outflow of the lake, caused the temperature to increase and oxygen levels to decrease. So the mussels could not survive. Reasons for the reduction in water level is not yet understood.

As previously mentioned, FWPM used to be widespread and common throughout the entire UK. The decline of the FWPM is almost entirely linked to human interference. It is certain that the decline in the mussel is evidence of a serious decline in water quality in the UK. It is no coincidence that it is in the North of Scotland, where the human population is very low, that the mussel exists in their greatest numbers.

FWPM are a keystone species in the rivers in which they live, as well as an important indicator species of river health and pollution levels. So does the FWFM deserve the £900,000 of government funding more than people do? In my personal opinion they do. The preservation of any species in decline is extremely important, never mind one threatened with extinction. This is likely our last chance to save the Freshwater Pearl Mussel, and it deserves all the money it can get. We are the root cause their destruction, and we owe them this much.


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Ben Wright

Ben Wright

I am a consultant ecologist with a special interest in protected species and birds. I have some past experience in science writing. I formally wrote a science column for a local paper, and composed a book based on the column (Science Matters) which has just been published.

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2 Responses

  1. Avatar Peter Howe says:

    Thanks for writing this, I cringed when I heard Mrs Jones say “My sympathies to the mussels but I need my community protected” on last nights news.
    I tweeted not to blame the mussels but fell on deaf ears!
    I think it is purely a lack of any understanding of wildlife with far more education needed and stop putting the blame on wildlife for the flooding.
    Even today on BBC2’s Jeremy Vine show they were blaming other floods on otters, with one person even suggesting lifting the habitat and putting it, with the butterflies etc elsewhere, unbelievable.
    When will it hit home that decades of poor land management practices higher upstream in the hills above them are mainly to blame.
    I remember seeing lots of harvested FWPM when I was a young boy at Grove Ferry in Kent and wonder if they still exist in the lakes there?
    Let’s hope these mussels make some kind of a come back in the future

  2. Avatar Ben says:

    Thanks. Seeing her ignorant comment on nationwide TV made me pretty mad. I’ve aided a few FWPM surveys up here in Scotland so I feel some sort of affection for them I guess

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