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Pilot Study of Seal Predation On Salmon Stocks in Irish Rivers and Estuaries

31st January 2014
Pilot Study of Seal Predation On Salmon Stocks in Irish Rivers and Estuaries

#MarineWildlife - Inland Fisheries Ireland (IFI) funded the Coastal and Marine Research Centre (CMRC) and University College Cork, in conjunction with partners in UCC's School of Biology, Ecology and Environmental Science (BEES) and the Marine Institute to undertake a two-year pilot study to investigate seal predation on salmon stocks in the Moy and Slaney estuaries.

In the study, which began in August 2011 and continued to August 2013, salmonids were found in the diet of both grey and harbour seals using identification of salmonid bones recovered from the scat (faeces) of seals collected at seal haulout sites in the Moy and Slaney.

Salmonids were recovered in relatively low numbers, representing only 1.6% of the total prey numbers in the Slaney in Co Wexford and less than 5% in the Moy in Co Sligo. But due to the large size of individual salmonids, they comprised approximately 15% of the total prey biomass consumed.

The presence of salmonids in the diet of seals is likely to represent consumption of both salmon (Salmo salar) and sea trout (Salmo trutta), with contribution to the diet related to seasonal abundance.

Genetic techniques were employed to confirm salmonid species identification based on hard structures, with both salmon and sea trout DNA being detected in scats.

The removal of salmonids by seals, or other predators, must be placed into context of the amount removed by fisheries. In the Moy, 6,564 salmon were caught (non-­release) by rod fisheries (five-year average, P Gargan IFI pers comm) which is likely to be far higher than that removed by seals in the area.

However, smaller salmon population units are most vulnerable to predation, and even low levels of predation by 'specialist' seals (or other predators) could have disproportionately large effects on small salmon population units such as in the Slaney.

The full report is available to download as a 4.3MB PDF file HERE.

Published in Marine Wildlife
MacDara Conroy

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MacDara Conroy

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MacDara Conroy is a contributor covering all things on the water, from boating and wildlife to science and business

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Marine Wildlife Around Ireland One of the greatest memories of any day spent boating around the Irish coast is an encounter with marine wildlife.  It's a thrill for young and old to witness seabirds, seals, dolphins and whales right there in their own habitat. As boaters fortunate enough to have experienced it will testify even spotting a distant dorsal fin can be the highlight of any day afloat.  Was that a porpoise? Was it a whale? No matter how brief the glimpse it's a privilege to share the seas with Irish marine wildlife.

Thanks to the location of our beautiful little island, perched in the North Atlantic Ocean there appears to be no shortage of marine life to observe.

From whales to dolphins, seals, sharks and other ocean animals this page documents the most interesting accounts of marine wildlife around our shores. We're keen to receive your observations, your photos, links and youtube clips.

Boaters have a unique perspective and all those who go afloat, from inshore kayaking to offshore yacht racing that what they encounter can be of real value to specialist organisations such as the Irish Whale and Dolphin Group (IWDG) who compile a list of sightings and strandings. The IWDG knowledge base has increased over the past 21 years thanks in part at least to the observations of sailors, anglers, kayakers and boaters.

Thanks to the IWDG work we now know we share the seas with dozens of species who also call Ireland home. Here's the current list: Atlantic white-sided dolphin, beluga whale, blue whale, bottlenose dolphin, common dolphin, Cuvier's beaked whale, false killer whale, fin whale, Gervais' beaked whale, harbour porpoise, humpback whale, killer whale, minke whale, northern bottlenose whale, northern right whale, pilot whale, pygmy sperm whale, Risso's dolphin, sei whale, Sowerby's beaked whale, sperm whale, striped dolphin, True's beaked whale and white-beaked dolphin.

But as impressive as the species list is the IWDG believe there are still gaps in our knowledge. Next time you are out on the ocean waves keep a sharp look out!

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