20090614-JMS-0028

ACOUSTIC SIGNALS

Sperm whales are an acoustically active species, constantly producing echolocation signals to navigate and forage in their deep ocean habitat. In the high latitudes, male sperm whales predominantly use three acoustic signal types: usual clicks, creaks (buzzes), and clangs (slow clicks). Usual clicks and creaks are the most thoroughly studied and understood signals, and are used in echolocation. Little is known about clangs, which have a more resonant ringing quality to them, and have been documented only by males both in the warm tropical breeding grounds and high latitude feeding grounds.

Sound is hypothesized to be generated in vibrations of fatty tissues below the blowhole called the museau de singe, or Monkey Lips. From here, Zimmer et al. theorize that part of the signal escapes through the forehead directly, while the remaining energy is transmitted back through the spermaceti organ, reflects off the frontal air sac, and transmits back through the junk and out the forehead. This occurs within 25-30 milliseconds, made up of 3 or more peaks of energy within a single click or pulse. The diagram below shows the Monkey Lips (Mo) below the Blowhole, with the initial pulse (P0) escaping directly out the forehead, while the remaining energy travels back through the spermaceti organ (So), bouncing off the frontal air sac (Fr), and escaping through the forehead as P1 and P2.

PmHeadStructure

 

Sound

USUAL CLICKS

PmClicks20sec_ChristiRob(8)_20110523T224020_2

Usual clicks are the most commonly produced signal by sperm whales, and have an Inter-Click-Interval of approximately 1 second. That is, a sperm whale clicks about once every second. This signal is believed to serve a variety of functions including echolocation and communication. Clicks can be detected on an underwater hydrophone over 30 miles away, allowing SEASWAP researchers to track sperm whales at great distances.

 

CREAKS

PmCreak_20sec_20120508T153135(2)

Creaks, also referred to as buzzes, are clicks at a very fast repetition rate of about 0.2 seconds. These signals are thought to be associated with foraging, where animals increase their click rate as they hone in on a prey item, terminating in a creak, which also sounds like a buzz. This theory draws from similar echolocation studies done with bats, where echolocation clicks speed up into terminal buzzes when bats hone in on prey items such as moths. These foraging creaks are extremely important to SEASWAP, as they potentially serve as a metric for depredation. Researchers review acoustic data collected on underwater hydrophones to count individual creaks produced by whales during fishing hauls in an attempt to quantify depredation rates.

CLANGS

PmClang_30sec

Clangs are the least understood signal made by male sperm whales in high latitudes, and are referred to in most literature as ‘slow clicks’. The are distinguished by their resonant quality and metallic timbre as well as their slower repetition rate than usual clicks, occurring once every 5-8 seconds. Clangs seem to be produced in clusters or trains, sometimes set apart from usual clicks before and after a train by a silence. They are most likely to be produced on the ascent of dives, or at the surface, rather than on the descent or bottom phase of dives. In the Gulf of Alaska they are thought by SEASWAP researchers to be used in communication, either over large distances, or as a sort of contact call between whales in the same area.

SPERMACETTI ORGAN

The spermaceti organ is a large, dorsally placed, conical tube filled with liquid spermaceti oil. It is terminated at the front end by one of two tough connective tissue lips, the so-called monkey lips or museau de singe, and at the back end by the frontal air sac that in turn is connected to the right nasal passage. The top and sides of the spermaceti organ are covered by a tough connective tissue sheath, the case, and a complex layer of tendons and muscles innervated by a rich supply of blood vessels and densely packed bundles of motor neurons.

JUNK COMPLEX

The spermaceti oil in the junk complex is contained in a sponge-like tissue structure where so-called wafers of tissue with higher oil content are interspaced by a connective tissue matrix with lower oil content. Compared to the spermaceti organ, this structure made the oil extraction considerably more difficult for the whalers, hence the term “junk.”