Aerial thermal-imaging survey of seals in Ireland 2017 to 2018

Abstract

In August of 2017 and 2018, the Sea Mammal Research Unit (SMRU) of the University of St Andrews carried out an aerial thermal-imaging survey of Harbour Seal (Phoca vitulina vitulina) and Grey Seal (Halichoerus grypus) numbers and distribution around Ireland. The survey was commissioned by the National Parks and Wildlife Service (NPWS), Department of Culture, Heritage and the Gaeltacht (DCHG) and it was the third such nationwide survey of seals in Ireland in summer. Previous thermal-imaging surveys were carried out in 2003 and in 2011/2012. In the 2017/2018 survey, 4,007 Harbour Seals were counted, compared with 3,489 counted in 2011/2012 (Duck & Morris, 2012; 2013) and 2,955 counted in 2003 (Cronin et al., 2004; 2007). The Irish coast was divided into five regions, East, South-east, South-west, West and North. The greatest proportion of Harbour Seals was found in the West region in all three surveys (41% in 2017/2018, 43% in 2011/2012 and 32% in 2003). The North and South-west regions had similar, but lower, proportions to previous surveys (27% and 28% respectively in 2017/2018; 25% and 28% in 2011/2012; 31% and 32% in 2003). The smallest proportions were in the East and South-east (3% and 1% in 2017/2018; 3% and 2% in 2011/2012; 4% and 1% in 2003). In 2017/2018, 3,698 Grey Seals were counted in Ireland compared with 2,964 counted in 2011/2012 and 1,309 counted in 2003. The Grey Seal count in 2017/2018 was 25% higher than the 2011/2012 count and almost three times higher than the 2003 count. The numbers of Grey Seals in the five Irish regions used to describe distribution in this report were not as consistent across the three surveys as were Harbour Seal numbers. In all three surveys, the greatest proportions of Grey Seals were counted in the west of Ireland (32% in 2017/2018; 40% in 2011/2012; 28% in 2003). In the east, south-east and south-west the Grey Seal count was substantially higher in 2017/2018 than in 2011/2012. In the west and north of Ireland the 2017/2018 Grey Seal count was slightly lower than in 2011/2012. The survey results suggest that the populations of both species are either stable or increasing in all regions of Ireland. The 2017/2018 survey produced the highest total count of the three nationwide summer surveys for both species. The 2017/2018 survey found that there is currently only very little spatial overlap between major haul-out aggregations of Harbour Seals and Grey Seals.

The NPWS Project Officer for this report was: Oliver O’Cadhla; Oliver.O'Cadhla@chg.gov.ie This IWM was edited by Loraine Fay and Ferdia Marnell