Abstract
AimEurope's only globally critically endangered seabird, the Balearic shearwater (Puffinus mauretanicus), is thought to have expanded its postbreeding range northwards into UK waters, though its at sea distribution there is not yet well understood. This study aims to identify environmental factors associated with the species’ presence, map the probability of presence of the species across the western English Channel and southern Celtic Sea, and estimate the number of individuals in this area.LocationThe western English Channel and southern Celtic Sea.MethodsThis study analyses strip transect data collected between 2013 and 2017 from vessel‐based surveys in the western English Channel and southern Celtic Sea during the Balearic shearwater's postbreeding period. Using environmental data collected directly and from remote sensors both Generalized Additive Models and the Random Forest machine learning model were used to determine shearwater presence at different locations. Abundance was estimated separately using a density multiplication approach.ResultsBoth models indicated that oceanographic features were better predictors of shearwater presence than fish abundance. Seafloor aspect, sea surface temperature, depth, salinity, and maximum current speed were the most important predictors. The estimated number of Balearic shearwaters in the prediction area ranged from 652 birds in 2017 to 6,904 birds in 2014.Main conclusionsAreas with consistently high probabilities of shearwater presence were identified at the Celtic Sea front. Our estimates suggest that the study area in southwest Britain supports between 2% and 23% of the global population of Balearic shearwaters. Based on the timing of the surveys (mainly in October), it is probable that most of the sighted shearwaters were immatures. This study provides the most complete understanding of Balearic shearwater distribution in UK waters available to date, information that will help inform any future conservation actions concerning this endangered species.
Highlights
Our estimates suggest that the study area in southwest Britain supports between 2% and 23% of the global population of Balearic shearwaters
This study provides the most complete understanding of Balearic shearwater distribution in UK waters available to date, information that will help inform any future conservation actions concerning this endangered species
We evaluated the predictive accuracy of the predictive Generalized Additive Models (GAMs) by their area under curve (AUC), where 0.5 indicates the model has no predictive ability, 0.7–0.8 shows the model is acceptable, 0.8–0.9 indicates the model is excellent, and anything higher than 0.9 is outstanding (Hosmer & Lemeshow, 2000)
Summary
With global population estimates ranging from 10,000 to 30,600 individuals (Arcos, 2011a; Arroyo et al, 2016; Ruíz & Martín, 2004), demographically informed population viability models suggest that without action Balearic shearwaters (Puffinus mauretanicus, Lowe 1921) are likely to face global extinction in the few decades (Genovart et al, 2016; Oro et al, 2004) Their relatively small and apparently rapidly declining population (Meier, 2015), restricted breeding range, and very low survival rates compared to similar species (Genovart et al, 2016) make them the only globally critically endangered seabird in Europe (BirdLife International, 2018). The distribution of immature shearwaters is not well understood, so conservation measures have not been targeted at immatures anywhere across their range
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