Sound production behavior of individual North Atlantic right whales: implications for passive acoustic monitoring

Abstract

Passive acoustic monitoring is being used to detect vocalizing marine mammals. Data on call types and individual rates of sound production are necessary to use passive acoustics to identify species, assess individual detectability, and estimate the number of individuals present. The present study describes the sound production behavior of endangered North Atlantic right whales Eubalaena glacialis in the Bay of Fundy, Canada, during July and August, recorded with suction cup archival tags (Dtag) in 2000 to 2002 and 2005. The Dtag simultaneously recorded acoustic data from a hydrophone along with the depth and orientation of the whale. Over 168 h of acoustic data were obtained from 46 tag deployments (35 ind.), with an average attachment dura- tion of 4.5 h. The rate of sound production was variable, ranging from 0 to 200 calls h �1 (mean ± SD: 6.4 ± 29.8 calls h �1 ), with 28 of the 46 tagged whales producing no calls (corresponding to 69/168 h of data). Right whale sounds from any whale in the area were recorded on most tag records, indicating that aggregations of whales may be detected more reliably than individuals. Calling rates were highest during surface activity and traveling and lowest during foraging and logging behavior. Whales of both sexes and all age-classes produced upcalls and other tonal calls, and 1 adult male produced gunshot sounds. The present study provides insight from the largest extant collection of recordings of individual North Atlantic right whales into the acoustic detectability of individual right whales and demonstrates that the behavioral state is the primary factor affecting calling rate.