ABSTRACT: I point out errors in data presentation and interpretation and weaknesses in the methods used by Gargan et al. (2016; Aquacult Environ Interact 8:675-689) to describe sea trout and fisheries in the Erriff River system, Ireland. Based on my findings, 13 of the 15 response variables which relate to sea trout are compromised. As a result of these failures, the overall findings and conclusions by Gargan et al. (2016) may also be compromised and invalidate their assessment of the characteristics of sea trout in the Erriff system, especially for the years 1985-2004. There are also serious chronological errors in Gargan et al. (2016), some of which have recently been corrected (see www.int-res.com/abstracts/aei/v8/c_p675-689/). Their analysis concerns the structure of sea trout populations before and after the widely reported collapse of West of Ireland sea trout stocks in 1989/1990—but not before and after the commencement of salmon farming in Killary Harbour as originally alleged in Gargan et al. (2016). With regard to the remaining 2 response variables, which relate to sea lice, no attempt has been made in Gargan et al. (2016) to link sea lice to changes in the Erriff sea trout population.