This species has regularly been referred to as a subspecies of the Twaite Shad (Alosa fallax). However, research has demonstrated that its ecological, molecular and morphological traits are sufficiently distinct for it to be regarded as a distinct taxon (Jolly et al. 2012, Coscia et al. 2013).

The Killarney Shad is endemic to a single small lake in southwestern Ireland. It has an extent of occurrence (EOO) of c.24 km², which comprises one location and meets the range size threshold for Critically Endangered under Criterion B1 (EOO < 100 km²). However, it does not meet any of the other conditions required for Criterion B, and its population trend is inferred to be stable meaning it does not approach any threshold for Criterion A. The extant population is estimated to comprise <10,000 mature individuals, which meets the threshold for Criterion C, but the population trend does not approach the thresholds for criteria C1 or C2. It does not meet the population size thresholds for Criterion D, and there exists no quantitative analysis which would permit application of Criterion E.

Therefore, this species is assessed as Vulnerable under Criterion D (D2) since its range is very small and it could plausibly become Critically Endangered or Extinct in a very short time period based on at least two future threats (introduction of invasive non-native fish or mollusc species and reduced habitat quality driven by climate change represent plausible future threats).

This species is endemic to Lough Leane in Killarney National Park, southwestern Ireland. Presence in the connected Lough Muckcross has never been unambiguously confirmed, and if any individuals do enter they are likely to be vagrants.

The results of field surveys conducted from 2007-2018 demonstrate that this species' current population trend is stable.

In September 2017, the overall population was estimated to comprise 17,478 individuals, of which 7,166 (41%) were adults. The population size thus meets the threshold for the Vulnerable category under Criterion C (< 10,000 mature individuals).

Lough Leane is the lowermost and largest of the three Lakes of Killarney, which also include Lake Muckross and Lake Upper. It is drained by the River Laune, which flows into the Atlantic Ocean at Castlemaine Harbour. The Killarney Shad does not inhabit the smaller lakes or the river, however, and appears to be completely landlocked in Lough Leane.

Its life history is not well-studied, but it is anecdotally reported to spawn on littoral shelves with gravel substrata, plus stony shorelines with a moderate gradient and diverse depth-velocity conditions. The stomach contents of individuals sampled during summer were composed almost entirely of zooplankton, with no evidence of piscivory identified.

Declining water quality in the naturally oligotrophic Lough Leane was identified in the early 1970s. Its trophic status over the following three decades fluctuated between mesotrophic and eutrophic, culminating in hypertrophic conditions and a major algal bloom in 1997. The increase in nutrients, particularly phosphorus was primarily associated with agricultural and domestic pollution.

The situation has improved since the Killarney Waste Water Treatment Plant was upgraded in 1985 and 1997. Changes in national legislation regarding phosphorous export from agriculture and a slight decline in cattle farming within the lake catchment are also thought to have contributed.

The lake's ecological status was assessed as 'good' in the wake of the most recent (2010-2015) European Water Framework Directive evaluation. Eutrophication remains a threat, however, with agricultural pollution difficult to control since it is primarily transported via river flow from sources outside the National Park. In addition, research has demonstrated that the wastewater treatment plant continues to contribute around 35% of the phosphorus load over the course of each year, and it is typically the major source during periods of low rainfall.

The introduction of invasive non-native fish or mollusc species and reduced habitat quality driven by climate change represent plausible future threats.

Lough Leane is a popular site for recreational fishing, and this shad is sometimes targeted.

This species is included in Appendix III of the Bern Convention (as Alosa fallox) plus Annexes II and V of the European Union Habitats Directive (as Alosa spp.). The entirety of Lough Leane lies within the boundaries of Killarney National Park, which was designated a UNESCO biosphere reserve in 1981. The National Park itself comprises part of the larger Killarney National Park, Macgillycuddy's Reeks and Caragh River Catchment SAC, which is included in the European Union's Natura 2000 network of protected areas (site IE0000365) with the Killarney Shad among the target species.

Efforts undertaken to reduce the levels of nutrients entering the lake since the mid-1980s have been partially successful, but it remains in a mesotrophic state and pollution levels continue to fluctuate.

Regular fish stock surveys carried out since 2001 have revealed that the Killarney Shad population trend is stable, and no specific conservation actions are currently deemed necessary.