Quantitative analysis of Weddell seal (L e p t o n y c h o t e s w e d d e l

Abstract

The Weddell seal (Leptonychotes weddelli) has a large repertoire of underwater vocalizations. Twelve underwater calls subdivided into 34 call types were classified based on differences in frequency range, duration, repetition rate, number per series, presence or absence of harmonics, auxiliary sound usage, and contour. The repertoire also contains nine dependent auxiliary sounds. In summary, this study standardizes the description and terminology for underwater vocalizations, reports source sound-pressure levels, and reviews usage differences by male and female seals.

An assessment of the audibility of sound from human transport by breeding Weddell seals (Leptonychotes weddellii)

“…Only calls between 0.010 and 16 kHz were analysed because of the upper frequency limit (16 kHz) of the DAT recorder in long-play mode. This frequency range is less than that recorded for Weddell seal vocalisations (up to 20 kHz) (Thomas and Kuechle 1982); however, it allowed us to capture most calls.…”

“…193 dB re. 1 µPa at 1 m (Thomas and Kuechle 1982). Consequently, even at the closest distances or altitudes tested, the noise levels gen-erated from the anthropogenic sources were less than those of the loudest natural vocalisations.…”

“…This is because males actively hold territories under the pupping colony during this time of the year (Siniff et al 1977;Kooyman 1981). Even low levels of noise there-fore appear to have the potential to affect vocal behaviour in Weddell seals, particularly considering that male Weddell seals would likely be actively listening and communicating with other males and receptive females during this time (Thomas and Kuechle 1982).…”

“…Again, determining precisely what an animal is responding to in these situations is difficult, because the acoustic and visual components of the stimuli are difficult to separate. Thomas and Kuechle (1982) and Pahl et al (1997) Received noise level will also vary according to abiotic conditions. Variations in the efficiency of coupling of sound energy into the ice, and thus into the water, imply that under-water received noise will vary depending on ice conditions.…”

“…Vocalisations were categorised as per Thomas and Kuechle (1982) and Pahl et al (1997) with the addition of one call type: the tongue click, which we included as a new category (Table 4). For each record-ing the following parameters were quantified: (1) call type (for each of the first 100 calls); (2) call duration; (3) number of elements within each call; (4) whether the focal call was overlapped, i.e.…”