Biosonar, dive, and foraging activity of satellite tracked harbor porpoises (Phocoena phocoena)

Abstract

This study presents bioacoustic recordings in combination with movements and diving behavior of three free‐ranging harbor porpoises (a female and two males) in Danish waters. Each porpoise was equipped with an acoustic data logger (A‐tag), a time‐depth‐recorder, a VHF radio transmitter, and a satellite transmitter. The units were programmed to release after 24 or 72 h. Possible foraging occurred mostly near the surface or at the bottom of a dive. The porpoises showed individual diversity in biosonar activity (<100 to >50,000 clicks per hour) and in dive frequency (6–179 dives per hour). We confirm that wild harbor porpoises use more intense clicks than captive animals. A positive tendency between number of dives and clicks per hour was found for a subadult male, which stayed near shore. It showed a distinct day‐night cycle with low echolocation rates during the day, but five times higher rates and higher dive activity at night. A female traveling in open waters showed no diel rhythm, but its sonar activity was three times higher compared to the males'. Considerable individual differences in dive and echolocation activity could have been influenced by biological and physical factors, but also show behavioral adaptability necessary for survival in a complex coastal environment.

Discrimination of fast click series produced by tagged Risso's dolphins (Grampus griseus) for echolocation or communication

“…These characteristics parallel those described in bats (Griffin et al, 1960) and other odontocetes, such as bottlenose dolphins (Au and Benoit-Bird, 2003), porpoises (Linnenschmidt et al, 2013), sperm whales (Miller et al, 2004) and beaked whales . Grampus griseus buzzes have a stereotyped pattern of decreasing ICI as a function of time (−11 μs per click).…”

Diurnal variation in harbour porpoise detection—potential implications for management

“…Acoustic detections are more susceptible than visual surveys to behavioural changes of the animal, such as differences in body orientation, click intensity and also periods of silence that could influence the results. Harbour porpoises show variation between individuals in their echolocation patterns (Linnenschmidt et al 2013). Unless porpoises echolocate, they will not be detected by an acoustic recorder, and given the narrow beam width of their echo location clicks (Goodson & Sturtivant 1996, Koblitz et al 2012, the direction that an animal is facing can substantially influence the probability that it will be detected even if it is echolocating.…”

Whistle characteristics and daytime dive behavior in pantropical spotted dolphins (Stenella attenuata) in Hawai‘i measured using digital acoustic recording tags (DTAGs)

“…Echolocation-based foraging activity has been described as regularly spaced echolocation clicks that decrease in interclick interval and end with a terminal buzz, which is characterized by a rapidly increasing click rate, presumably during the final phase of prey capture (Johnson et al, 2004;Aguilar Soto et al, 2008;Linnenschmidt et al, 2013;Wisniewska et al, 2016). The physical attachment of the tag to the animal's body allows coupling of low frequency energy (<15 kHz) from the body to the tag, therefore, focal echolocation clicks and buzzes can be identified spectrally based on the presence of low frequency energy (Zimmer et al, 2005;Johnson et al, 2006).…”

“…Dive data may provide insights into foraging behavior and how animals use the water column, which may be used to inform development of acoustic deterrent devices and alterations to fishing practices or gear to reduce marine mammal bycatch (Westgate et al, 1995;Baird et al, 2001;Mooney et al, 2007;Linnenschmidt et al, 2013). Basic acoustic data may provide informative context for dive behavior (Watwood et al, 2006) and concurrent sampling of these data types, as with digital acoustic recording tags, can elucidate responses to anthropogenic noise (Tyack et al, 2011).…”