Pádraic Fogarty lists the North Atlantic right whale or Nordcapper (also known as the Northern Right Whale) as one of the mammals extinct in Ireland since human habitation here:
Regularly occuring up to 1910, a handful of records since then but none in recent decades.
Whale conservation and whaling are possibly the emotive issue in conservation. The International Whaling Commissions’s moratorium, obviously not observed by some nations, seems to have been an overall success in restoring humpback whale populations. Other whales, however, have not shown this bouncebackability – the blue most famously.
The name alone of the right whale outlines its vulnerability – it was the “right” whale to hunt, slow moving, allowing approaches, and did not sink once killed. In the rather sadly predictable fashion of the dodo and the this availability as a food stuff led to massive exploitation. It hasn’t followed those species into total extinction.
From the Wikipedia:
In the eastern North Atlantic, the right whale population probably numbers in the low double digits at best, with little information known about their distribution and migration pattern. Scientists believe that this population may be functionally extinct
Entire European regions including French coasts, Hebrides, North Sea and Baltic Seas, and further north up to Swedish, Norwegian and Svalbard areas were once ranged by whales. Phenology of catch records in the early twentieth century in Nordic countries shows that whale presences in northern waters was at peak in June. In Ireland, catches were concentrated in the first half of June until 1930s and preceded catch in the Scottish bases of the Hebrides which were concentrated in the second half of June and July, and this indicates that those whales were likely to migrate along Irish coasts. Of all modern whaling grounds in European waters, Hebrides and the Shetland Islands were the center of whaling in the early 20th century, and any records afterwards these catches became scarce in eastern Atlantic where only two cow-calf pairs had been documented
The Irish Dolphin and Whale Group page on the right whale mentions confirmed sightings in Irish waters off the Donegal coast (how far isn’t mentioned) The Wikipedia includes a link to the IWDG page as a source for “Two observations” in the “1990s or 2000s” off the Donegal coast – one of only four (possible) observations in the whole Eastern Atlantic since 2000 listed.
Right whales are sensitive to noise, and the events of September 11th 2001 allowed a natural experiment to take place which helped quantify this:
Baleen whales (Mysticeti) communicate using low-frequency acoustic signals. These long-wavelength sounds can be detected over hundreds of kilometres, potentially allowing contact over large distances. Low-frequency noise from large ships (20–200 Hz) overlaps acoustic signals used by baleen whales, and increased levels of underwater noise have been documented in areas with high shipping traffic. Reported responses of whales to increased noise include: habitat displacement, behavioural changes and alterations in the intensity, frequency and intervals of calls. However, it has been unclear whether exposure to noise results in physiological responses that may lead to significant consequences for individuals or populations. Here, we show that reduced ship traffic in the Bay of Fundy, Canada, following the events of 11 September 2001, resulted in a 6 dB decrease in underwater noise with a significant reduction below 150 Hz. This noise reduction was associated with decreased baseline levels of stress-related faecal hormone metabolites (glucocorticoids) in North Atlantic right whales (Eubalaena glacialis). This is the first evidence that exposure to low-frequency ship noise may be associated with chronic stress in whales, and has implications for all baleen whales in heavy ship traffic areas, and for recovery of this endangered right whale population.