Evidence for successive breaching events by basking sharks Cetorhinus maximus (Lamniformes: Cetorhinidae)

Abstract

Basking sharks were recorded breaching frequently off the coast of Co Clare, Ireland. The frequency and time between breaching events were analysed to determine any patterns in this behaviour. A total of 93 breaches of basking sharks were recorded over a 3-day period in September 2020. The mean number of breaches per hour, during a total observation period of 515 min, ranged from 6.0 to 15.3 with a mean ± SD of 9.2 ± 4.3 breaches per hour. Inter-Breach-Intervals (IBI) ranged from less than 1 min to a maximum of 34 min with a mean value of 5.4 min (median 2.0 min) across all observations. A total of 39.8% of all breaches were recorded within 1 min of the previous breach, whilst 65.6% were made within 5 min. Results suggest one breaching event may act as a trigger for other breaching events.