Environmental data:
Sunrise, sunset and civil twilight times were extracted from
(www.timeanddate.com/sun) for
Sherkin Island, and were used to calculate the diel cycle phases
(morning, day, evening, and night) (Carlström, 2005; Todd et al. ,
2009). Tide data were extracted from tide tables for Roaringwater Bay
(www.tides4fishing.com/ie/munster/roaringwater-bay).
Time difference to nearest high tide was calculated, as well as phases
of the tidal cycle (ebb/flow/high/low water). Tidal range was also
calculated as an indicator of spring and neap tides. Hourly water
temperature data were obtained from the PODs, taken as the average value
recorded by both PODS to avoid any recording bias between PODs. While
the PODs cannot provide a direct measure of environmental noise levels,
the click detection algorithms record unfiltered short click-like events
within the 20kHz – 160kHz bandwidth (Nall ), and is recorded for
each sampling minute. A positive correlation has been found betweenNall and environmental noise levels using a full-bandwidth
recorder and is used as a proxy for general noise levels (Clausen et
al., 2018; Nuuttila et al., 2018). We included this in models to
investigate the effect of varying environmental noise levels on POD
detection performance. For the purpose of interpretation of the results,
seasons were defined as Spring (March to May), Summer (June to August),
Autumn (September to November) and Winter (December to February).