cetaceans

Recordings from acoustic tags show that five Blainville's beaked whales produced mid-frequency broadband sounds on all of their deep dives, with each sex producing two different sound types. These broadband sounds are atypical of the regular echolocation sounds previously described for this species. One male produced a total of 75 sounds over four dives, between the depths of 109 and 524 m, and four females produced a total of 71 sounds over 18 dives, between the depths of 305 and 1289 m. Ninety-six per cent of the male sounds and 42% of the female sounds were produced before the onset of foraging echolocation sounds, and all were produced before the deepest point of the dives. Apparent source levels of the sounds ranged from 124 to 132 dB re 1 µPa (RMS) @1 m. These sounds may be candidate communication signals, with their production timed to mitigate the risk of both predation and hypoxia.

A new method for the automated detection of sperm whale clicks that combines neural network and statistical computations is presented. This method is intended to detect regular clicks and creaks and can be broken down into two main processing stages. The first stage works with the spectrogram output by computing the accumulated energy along each time frame, extracting consecutive two-seconds length time windows, obtaining statistical parameters characterizing these time windows and classifying them using a feed forward neural network as either containing regular clicks, creaks or noise. In the final stage a dynamic energy-based criterion is applied to each classified time windows based on previously computed statistical parameters. The performance of the method has been tested with three long recordings containing regular clicks and creaks and shows significantly high percentages of correct detections (global score of 94.8%) with a reduced computation time.

The minke whale (Balaenoptera acutorostrata) is a small, elusive baleen whale that is rarely sighted in tropical waters of the North Pacific Ocean. During winter and spring, they produce songs, also known as ‘boings’, that are commonly detected at deep water hydrophones located around the Hawaiian Islands. We acoustically monitored minke whales using a fixed seafloor hydrophone array encompassing a large ( >2000 km2), deep-water area off the island of Kauai. Simultaneous visual-acoustic surveys of the same region were conducted from a quiet motor-sailing vessel. The combination of the towed and fixed hydrophone arrays allowed animals to be localized and tracked in near real-time. Using both methods, we were able to visually confirm the location of a minke whale initially detected and localized using the fixed hydrophone array, and later with the towed hydrophone array. These data are being collected to help validate statistical methods that are being developed to estimate densities of marine mammals using acoustic signals they produce. In a related study, boings recorded in the Hawaiian Islands (central North Pacific) were acoustically characterised and compared to boings recorded in the western and eastern North Pacific. These results are discussed in relation to the behaviour and population biology of this species. We provide recommendations for tracking, monitoring behaviours and estimating the distribution and distribution of these vocally active, but visually elusive whales.

The NEMO-OvDE platform, deployed on the seabed at a depth of 2050 m, 21 km off the coast of Catania in Sicily (Italy), has provided the opportunity to better understand the presence and behaviour of sperm whales in the area. Equipped with four wideband hydrophones (30Hz-40kHz) forming a tetrahedral array of 1 m side, the platform sent digital data to the land station continuously 24h a day from January 2005 to November 2006. 7359 samples, for a total of 613 hours, were recorded and analyzed to determine the presence of sperm whales. Analyses were performed by trained operators with the use of SeaPro, a real-time spectrographic software, to distinguish species, number of individuals present and sound categories emitted. Sperm whale presence is considered as low density in the Ionian sea by an acoustic survey of IFAW in 2004 and by other works done in the vicinity. However, in our study, an unexpected presence of animals was found, with 23% of files containing animals in both years. Then, we focused our study on codas, sounds typical of social groups and with a geographical connotation, which for the Mediterranean are usually emitted as the 3+1 pattern. Not enough is known about the Mediterranean population to determine the connections between geographical areas. 3+1 remains the most common pattern, but a surprising variety of patterns was found, linking these animals to the situation present along the Hellenic trench. We used GAMs to establish seasonal variations to understand the movements of the species in the Ionian sea. Spring is the season richest in codas due to the greater presence of individuals. For the first time we demonstrate a relation between the pattern performed and the number of animals. This can be interpreted as an evidence of a different behavioural meaning.

Visual and acoustic surveys have shown that endangered North Atlantic right whales overwinter in the waters of the Northeast US. Detailed knowledge of this population’s distribution is critical to reducing anthropogenic mortality events. Passive acoustic studies have confirmed that Stellwagen Bank National Marine Sanctuary (SBNMS) and Jeffreys Ledge are areas of high baleen whale acoustic activity during the winter. Right whales produce three main types of calls, the up-call, gun-shot and tonal calls. However, no thorough assessment has yet been made of whether this call type is the most appropriate one to use. SBNMS has been part of an ongoing passive acoustic study since 2006 and provides an opportunity for understanding the relationship between up-calls and gun-shots for this region. From December 18th 2007 to May 28th 2008 an array of 10 marine acoustic recording units was deployed in SBNMS. An automated detector was used to determine seasonal occurrence of calls. Gun-shots and upcalls occurred throughout the winter period, with gun-shots peaking in January, and up-calls peaking in December. Comparative analyses of up-calls and gun-shots show that they occur simultaneously around 17:00. Gun-shots primarily tended to occur between 16:00 and 4:00, while up-calls primarily occurred between 11:00 and 18:00. Average gun-shot activity was 2.15 calls/min, while average up-call activity was 3.45 calls/min. Future research should be directed towards assessing occurrence of different call types between seasons, and in the south-east US breeding grounds and northern foraging areas.

Currently, there is a lively public discussion about the pros and cons of keeping dolphins in captivity, and a growing number of people demand the rehabilitation of these creatures. However, such an enterprise is difficult to achieve if one wants to do it in a biologically adequate manner. A few months ago we started to tackle this matter by studying a group of bottlenose dolphins (for details see Todt & Hultsch, 1995, Europ. Res. Cetaceans, 9). The Tursiops truncatus group is living in semi-free confinement adjacent to the Red Sea (site: Dolphin Reef/Eilat; size of site: > 10.000 m², depth: 18 m; size of group: 5 adults (2/3), 3 juveniles (2/1), 1 call). The site is separated from the open sea by a wide-mesh net only, and has been recently a gate to the sea is open for two hours per day. For a long time, however, and otherwise than expected, only one individual made use of the opportunity to swim out for an excursion, whereas the other ones repeatedly inspected the gate without passing through completely. In order to further investigate why the dolphins seemed to have problems with such physical barriers, we built a new enclosure and invited the animals to explore and also to use it by voluntarily passing a second experimental gate. Then, we recorded how the dolphins coped with this setting (recording equipment linked to videocameras and hydrophones). Behavioural data were evaluated in terms of correlations between the vocalizations and stress-causing events, such as problems preceding or following any trial to pass the gate (for details of parametric analysis see Janik, Dehnhardt, Todt, 1994, Behav. Ecol. Sociobiol., 23, 15-21, or Hammerschmidt & Todt, 1995, Behaviour, 132, 381-399). Our results confirmed that bottlenose dolphins may indeed have problems in passing physical barriers. But they showed also how these animals finally solve such problems. In addition, the study documented a variety of vocalizations which were correlated to the quality of the particular test episodes or the animals' intrinsic state, respectively.

Social signals indicating the emotional state of the signaller are described as emotive signals. Their structure is often variable and graded. Emotive acoustic signals are associated with close proximity of animals often in combination with tactile and visual communication. By contrast, signals used for location and identification of conspecifics are mainly stereotyped and discrete. As yet, research on killer whale acoustic communication has focused mainly on discrete calls. Whistles, characterized by variable pure tones, are poorly investigated in killer whales and their function in communication remains unclear. In this study we classified whistles from different killer whale pods and examined whistle emission during different behavioural contexts. Simultaneous underwater recordings and surface behavioural observations were made on resident killer whales in the Johnstone Strait, British Columbia, in summer 1994. Whistles were analysed using a Real Time Spectrographic Analyser. Every acoustical clan of killer whales seem to produce whistles with some distinctive features. Whistles are produced more often during socialising than during any other behavioural category (foraging, travelling, resting, beach rubbing). During socialising killer whales form a group often in close body contact and engage in a variety of social displays: breaches, chasing, rolling over each other, and sexual behaviours. In this behavioural context whistles might serve as emotive signals indicating the emotional state of the signalling animal.

Field studies on cetaceans in the Mediterranean Sea have experienced a remarkable development in recent years. Research cruises aboard sailing vessels up to 19 m long were organized by Tethys Research Institute within the seas bordering the Italian peninsula and islands. From 1987 to 1990 recordings of underwater sounds produced by cetaceans in these waters were collected. Recordings were made with traditional reel-to-reel analog tape recorders and high quality underwater transducers. A total of about eight hours of underwater sounds of six odontocete and one mysticete species were recorded. These sounds were subsequently analyzed. The analysis of basic parameters such as duration and frequency range was performed on a Kay Sonagraph DSP 5500 at the Interdisciplinary Center for Bioacoustic Research of the University of Pavia. A cetacean sound library catalogue based on a commercial database was created in order to allow interaction with a PC-based DSP workstation equipped with optical disk for storage of digitized sounds. The aim of this sound library is to provide more information about the acoustic capabilities of cetaceans of the Mediterranean and to allow highly specific access to available data for a variety of potential future applications, such as research and didactical purposes. A current joint research program between Tethys Research Institute and the Center for Bioacoustic Research should provide further opportunities to increase the collected and analyzed data of this library. This research is supported by grants from the Italian Ministero della Marina Mercantile.

Humpback whale males produce complex sounds with a hierarchical organisation of 'units' 'phrases', 'themes', and 'songs' (Payne and McVay 1971). On 9 November 2000 the vocalisations of one humpback whale were recorded at Arraial do Cabo (23° 03' S; 42° 02' W), a migratory corridor of baleen whales. The recordings were obtained using a fixed hydrophone (CN 60; 40 m deep) and a Tascam DA-60 MK 11 digital tape recorder. The recordings were analysed with Cool Edit Pro 1.2 (6,000 Hz; 32-bit; mono; 512-pt Hamming windowed time slices with 100% overlap). 19 themes were identified from a song sample of 1h 27min. The units were classified in 3 categories: harmonic, modulated amplitude and impulsive sounds (Maeda et al. 2000). For 22min 66s, there was no repetitions of themes, forming a song cycle of 12 themes. In the remainder of the song, there was a mixture of unprecedented themes with some of the 12 initial themes. The theme 7 repeated three times, theme 5 twice and themes 9, 10, and 11 once each. Theme 7 showed a variation in the repetition rate of its phrase. On the first occurrence, the phrase repeated twice. On the second time, it repeated 12 times. On the third time, it repeated 11, and in the last, 5 times. Theme 5 only had a variation between 10 and 11 repetitions. The impulsive sounds themes 10 and 11 had no phrases. Theme 9 had its phrase repeated 8 and 3 times. Themes 6, 9, 13, and 17 had 8 units; they were the most diverse themes. Razafindrakoto (2001) observed a frequency shift in humpback whale songs when peak frequency was lower than the ambient noise. The singer could shift the frequency to avoid the ambient noise (Maeda et al. 2000). We also found this frequency shift (support: CAPES, CASOP - Brazilian Navy, Redley, Cetacean Society International and Whale and Dolphin Project).