Nearby Ship Likely Masks Beaked Whale Calls, Dive Cut Short
Soto, Johnson, Madsen, Tyack, Bocconcelli, Baorsani. Does intense ship noise disrupt foraging in deep-diving Cuvier's beaked whales (Ziphius cavirostris)? MARINE MAMMAL SCIENCE, 22(3): 690–699 (July 2006)
This paper reports on a single observation that suggests the need for further investigation: an acoustic digital tag was attached to a Cuvier's beaked whale, which then exhibited an unusual foraging dive pattern when a large ship passed nearby. The tag was attached for over 15 hours, during which the whale made eight deep dives, with typical click and buzz vocalizations recorded on all dives. During the fourth dive, a single large ship passed nearby, and the dive was seemingly cut short (42 minutes; the mean of the other 7 dives was 57 minutes). A key finding was that the ship noise included frequency components close to beaked whale clicks; the 15dB increase in ambient noise levels caused by the ship would decrease the maximum effective range of echolocation by more than half, and the maximum range of communication between whales by a factor of five (it is assumed that foraging at depth involves coordinated behavior among several whales, so that this vocalizing is important). The results presented here came from a Z. cavirostris tagged some 25 km south of the busy ports of Savona and Genoa. Dense vessel traffic in the area includes ferries (conventional and high speed), tankers, cargo ships, and recreational boats. While beaked whales in the area may well be habituated to moderate noise levels from ship traffic, the apparent response to a close ship approach reported here suggests that they may not habituate to the elevated noise levels from such a close approach, which may be less common.
D-tags Adapted For Use With Manatees - D-tags, which record the sound heard by an animal while tracking its motion in the water, have become a key tool in biologists' efforts to understand the effects of sound on cetaceans. Now, researchers have adapted D-tags for use with manatees (their non-invasive suction-cup attachment system had to be changed to work with rough-skinned manatees). Synchronizing boat sounds with the manatees' behaviors allows researchers to learn how manatees react -- or don't react, as filmed observations showed -- to boats. It will also allow researchers to determine if manatees react differently in shallow water versus deep water, where they might have more places to hide. This year, a total of 10 wild manatees were tagged. Florida State University researchers Doug Nowacek and Athena Rycyk said it is too early to draw conclusions about what they hear on the tags, although the sound files are interesting. “We hear a lot of chewing,” Nowacek said. Roars recorded from some passing boats was startling, Rycyk added. “When a boat flies by, especially a boat moving fast, it is really, really loud,” she said. What's more, boats can be heard for up to a minute before actually passing near the manatee. For years, Florida wildlife managers have asked boaters to slow down in areas populated by manatees. Reducing speed, they theorized, would give boaters a better chance of seeing and avoiding manatees on the surface and would give the animals fair warning to move away. But as the number of collisions has ballooned, critics have argued that manatees may not hear the motors of a slow-moving craft until the vessels are nearly on top of their backs. Recording sound will also help scientists learn about the sounds that manatees make: what type of vocalizations they use, how often they vocalize and how vocalizations change depending on their activity. Sources: Photonics, 10/16/07 [READ ARTICLE] WHOI Oceanus Magazine, 10/11/07 [READ ARTICLE]
