Robert McCauley

GEOGRAPHIC VARIATION IN SOUTH PACIFIC HUMPBACK WHALE SONGS

Every winter, (male) humpback whales (Megaptera novaeangliae) produce long complex songs. Song content is dynamic and singers incorporate changes as they occur, thus song is shared through cultural transmission. We compared songs recorded in winter migratory termini in Tonga, New Caledonia, Eastern Australia, and on migration paths off Eastern Australia and New Zealand, in the winter of 1994. Seven themes were shared by all regions, with an additional two themes shared by all but Tonga. Differences in regional variants were most pronounced between Tongan and Eastern Australian song. New Caledonian and Kaikouran song were more similar to songs from Eastern Australia rather than Tonga. These regional differences were stable across the season. The results suggest some migratory exchange among widely separate wintering regions of Area V, consistent with tag recovery data, but the time and location at which song sharing occurs remains speculative.

Long-term monitoring of soundscapes and deciphering a usable index: Examples of fish choruses from Australia

Similar to geophysical and anthropogenic noise, biological contributions to soundscapes vary considerably in frequency, time, and intensity. Fish choruses are a perfect example, contributing significantly to marine biological noise and are used here as an analogue for variations in soundscapes. Their species-characteristic signals vary thus, so do their choruses, which can raise ambient noise levels by up to tens of decibels, for prolonged periods. Multi-species choruses can occur, with varying degrees of temporal and frequency partitioning, or none at all. Australian datasets of underwater noise have been acquired for nearly two decades and multiple fish calling patterns have been detected. Detecting, delineating, and understanding these patterns is non-trivial and a metric relating their contribution to the soundscape with biodiversity or habitat would be an invaluable tool. In recent years, several acoustic indices have been derived, proving useful in the terrestrial domain. Investigation of their appl...

Issues associated with sound exposure experiments in tanks

For practical reasons it is often necessary to carry out sound exposure experiments on marine animals in tanks or pools that may have dimensions ranging from less than one meter to a few tens of meters. The boundaries of such tanks are almost invariably highly reflective to underwater sound, resulting in a sound field that can vary spatially in unexpected ways, and in which the relationship between pressure and particle velocity is quite different from that in an animal’s natural environment. In this paper a numerical simulation based on the finite difference method is used to illustrate these effects. The results show that, at frequencies below the tank’s lowest resonant frequency, the particle velocity and pressure fields vary smoothly in space and with changes in frequency, but that both the ratio of the particle velocity to the pressure and the way in which their amplitudes vary with distance from the source are different than in a free-field situation. At frequencies above the lowest resonant frequen...