I see otters often, and I have seen a Leisler's bat (but only a dead one). Never a red squirrel. Otter populations are vulnerable to anything that effects water quality, chemicals that accumulate in fish and nets.A new Red List of Irish terrestrial mammals was published in 2009 and all 26 terrestrial species native to Ireland, or naturalised in Ireland before 1500, were assessed. Of these, one was found to be regionally extinct (grey wolf Canis lupus), one achieved a threat status of Vulnerable (black rat Rattus rattus), three were found to be Near Threatened (Leisler's bat Nyctalus leisleri), otter (Lutra lutra) and red squirrel (Sciurus vulgaris)), one was data deficient (Brandt’s bat Myotis brandtii) and the remaining 20 were of least concern.
Ireland has only a small number of mammal species - 26 - but some of them are endangered - Daubenkin's Bat, the Otter and the red squirrel are all on the "Red List" as engangered.
European Red List of Endangered Species
Irish mammals - National Parks and Wildlife Service
Wikipedia List of Mammals in Ireland.