Beaked whale dive cycle estimation based on acoustic data from drifting recording systems

Most beaked whales have a stereotypical diving behavior that consists of a long, deep dive separated by one or more shallower dives (Baird et al., 2008; Tyack et al., 2006). Acoustic recording tags show that echolocation pulses are commonly produced only during a portion of the long, deep dives (Johnson et al., 2004; Warren et al. 2017), which has led to the characterization of those dives as deep foraging dives. This echolocation period is highly synchronous within a group with an estimated 99% overlap among individuals (Aguilar de Soto et al., 2020). The period between the start of one deep foraging dive and the start of the next is referred to as a dive cycle (Tyack et al., 2006). Although two deep foraging dives can occur consecutively after a single surfacing series (a short series of surfacings to breathe; Schorr et al., 2014), foraging dives are more typically separated by several surfacing series and shorter dives to intermediate depths (Tyack et al., 2006). The dive cycle duration of beaked whales has been estimated as the sum of the deep dive duration and the inter-deep-dive interval (IDDI; Tyack et al., 2006) or as the inverse of the mean dive rate (the mean number of deep dives divided by the hours of observation; Schorr et al., 2014). The dive cycle duration is an important parameter in estimating acoustic availability for acoustic-based abundance estimation methods (Barlow et al., 2021).