Mussel seed settled successfully at six monitoring locations along Ireland's southwest coast in 2025, according to the first findings from a Bord Iascaigh Mhara (BIM) research project aimed at helping shellfish growers improve the timing of seed collection.
The results, announced by BIM on Friday, 6 November, follow a significant failure of mussel seed collection in southwest Ireland in 2024, highlighting the vulnerability of rope mussel production to fluctuations in natural settlement.
The EMFAF-supported Southwest Mussel Larvae Monitoring Pilot Project is examining mussel spawning, the abundance of free-swimming larvae, their microscopic food supply and subsequent settlement on collection ropes.
Six Southwest Locations Monitored
The first year of monitoring covered Roaringwater Bay, Dunmanus Bay, Bantry Bay, Castletownbere, Ardgroom Harbour and Kilmackillogue Harbour, spanning important mussel-growing areas of Cork and Kerry.
Researchers recorded successful settlement at all six locations, although the numbers and sizes of young mussels varied considerably. Castletownbere recorded the highest concentrations of mussel larvae in the water, but high larval concentrations did not necessarily translate into equally strong settlement on collection ropes.
BIM says water movement, food availability and local conditions all affect where larvae travel and whether they settle and grow. The findings could help growers decide when to deploy collection equipment.
Supporting Ireland's Mussel Industry
According to BIM, Ireland's rope mussel industry produces more than 10,000 tonnes annually, worth over €7.5 million, and supports more than 220 jobs in coastal communities.
Growers rely on naturally occurring young mussels, known as spat, attaching to collection ropes. Unpredictable settlement therefore complicates production planning.
The challenges are not new. In Afloat's August 2025 report on aquaculture industry concerns, IFA Aquaculture identified poor mussel seed availability and settlement among the pressures facing both rope and bottom mussel producers.
Monitoring Expands Along Western Seaboard
The programme continues through 2026 and 2027, with additional monitoring at Killary Harbour, Clew Bay and Mulroy Bay. BIM says weekly test collectors will help pinpoint when settlement occurs and whether seed arrives in one main wave or several smaller pulses.
Joanne Gaffney, BIM's Aquaculture Technical Manager, said the monitoring is creating a long-term dataset that should improve understanding of the health and resilience of Ireland's mussel population.
The first-year report is available through BIM's aquaculture publications, with a second report expected in early 2027.
Although the 2025 results confirm settlement at all six southwest locations, they do not establish that the longer-term problems with unpredictable seed supply have been resolved.
