Update on North West Algal Bloom

The bloom that has been affecting areas of the North West from Mayo to Donegal and at lower concentrations down along the rest of the West coast continues to impact on coastal marine life in several areas.

Mr Joe Silke of the Marine Institute stated today “The bloom that reported by the Marine Institute in the North West over the past two weeks, has shown some signs of increase along the west coast in the past few days. We started to detect low levels of it in the water from late May, but in the past two weeks it developed into a dense bloom in parts of the north-western counties from the Mayo to Donegal area.

In the past week high levels have been detected in Galway Bay, but no mortalities have so far been reported in this region. In Donegal the bloom was so dense that there were many reports of discoloured red or brown water in some areas and several areas have reported dead marine life washing up on the shoreline requiring Local Authorities to close certain beaches.”

This is a one of several microscopic algae that occur naturally in coastal waters, this particular one is called Karenia mikimotoi. Dead fish on Rossnowlagh Beach Photo:Paddy Ennis While the algae is not harmful to humans it did result in large numbers of dead fish including turbot, flounder, scorpion fish and shore rockling in Inner Donegal Bay. Other dead species were worm pipefish, lesser weavers, grey gurnard, shanny, sand goby, pollock, sole, plaice, flounder and dabs which have been washing up on Rossnowlagh and Murvagh beaches and earlier this week red flags were raised. The Local Authorities took the decision to close both beaches in response to large numbers of dead fish but these restrictions have been lifted on Tuesday. The situation is being closely monitored by the Marine Institute and Donegal County Council who are both keeping the public informed as the situation progresses on their websites. Mortalities of marine organisms have also been reported from the Sligo and Mayo coastal regions.

Local sea anglers have reported low fish catches along the Donegal coast, and in some areas a complete absence of any fish. This is due to the bloom which fish will avoid when they can. Lobster and Prawn fishermen have also reported very poor catches in the Donegal area. Oyster farms in Donegal also were reported to have suffered losses of up to 80% of stocks in  some areas.

Mr Silke explained “The bloom affects species that live on or near the sea bed so we are seeing flatfish, lugworms and some shellfish getting washed up on the beaches. It is a natural bloom which we have seen it to occur in several places over the years. It is believed that it originates offshore as a natural part of its summer life cycle, and gets concentrated up against the coast with tidal and coastal currents.”

Some indications that the bloom may be moving back out to sea were observed in the latest satellite images and modelling data, however cell counts of samples analysed in the Marine Institute today show that the bloom is still of the same density in the Donegal and Sligo regions as it was last week, but increased levels were reported in Galway Bay.

The Marine Institute’s monitoring programme will continue to sample and monitor the bloom and post updates on our website at marine.ie and on local radio.