Aquatic Mammals

Published by Aquatic Mammals Journal

Print ISSN: 0167-5427


Table 1 . Weight changes of the pup and the weight of the 
Figure 5. The percentage of suckling sessions broken off by the mother and by the pup during each day of the suckling period. 
Figure 6. The total suckling time per day during the suckling period. 
Figure 9. The mother's daily food consumption before, during, and after the suckling period. Triangles indicate days on which no food was offered. 
The suckling period of a Grey Seal (Halichoerus grypus) while the mother had access to a pool.
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January 1991


160 Reads


P.R. Wiepkema


In January 1989 a Grey seal cow gave birth to a female pup at the Harderwijk Marine Mammal Park. Mother and pup were kept in an outdoor suckling area and the mother had free access to a pool. Constant observation of mother and pup provided comparable information on suckling parameters as in 1988 when the mother and her pup were confined to an outdoor suckling area. In contrast to the 1988 situation the following was found in the present 1989 study: (I) On average the pup vocalized more often before a suckling session. (2) Mother and pup spent less time together. (3) The mother rested less and spent a great deal of time swimming. (4) On average the suckling sessions were shorter, but the frequency ofsuckling was similar. This resulted in a shorter total daily suckling time. (5) The pup did not start to move around in the suck­ ling hollow during·the last 3 days before weaning. (6) The pup grew faster (2.2 kg/day) than in 1988. These differences were probably caused by the different weather conditions (the suckling period of 1988 was very wet, that of 1989 was completely dry), and by the different degrees of freedom of the mother.

Figure 1. Schematic overhead view onto research pool and set-up with the animal's position at its underwater station indicated
Figure 9. Examples of potentials evoked with tone pip in the harbour porpoise; sampling duration was 10 ms, and centre frequency of the stimulus was 2 kHz. Received level descended from 83 dB re 1 µPa (upper trace) in 5-dB steps to 73 dB (lower trace). Arrows indicate the positive and negative peak amplitudes used for threshold analysis. Dashed lines indicate equivalent peaks in the different traces.
Figure 10. Examples of EFR in a harbour porpoise to AM sound stimuli; sampling duration was 30 ms, carrier frequency was 22.4 kHz, modulation rate was 1.1 kHz, and modulation depth was 100%. Received level descended from 76 dB re 1 µPa (upper trace) in 3-dB steps to 67 dB re 1 µPa (lower trace).
Perception of Low-Frequency Acoustic Signals by a Harbour Porpoise (Phocoena phocoena) in the Presence of Simulated Offshore Wind Turbine Noise

January 2007


216 Reads



Bert Hoeve




This aricle was published in the journal, Aquatic Mammals [© European Association for Aquatic Mammals] and is also available at: Using auditory evoked potential (AEP) methods, a study was conducted on a harbour porpoise (Phocoena phocoena) at the Dolfinarium Harderwijk in The Netherlands. The study measured the audible range of wind turbine sounds and their potential masking effects on the acoustic perception of the animal. AEPs were evoked with two types of acoustic stimuli: (1) click-type signals and (2) amplitude-modulated signals. The masking noise resembling the underwater sound emissions of an operational wind turbine was simulated. At first, the animal’s hearing threshold was measured at frequencies between 0.7 and 16 kHz. Subsequently, these measurements were repeated at frequencies between 0.7 and 2.8 kHz in the presence of two different levels of masking noise. The resulting data show a masking effect of the simulated wind turbine sound at 128 dB re 1 μPa at 0.7, 1.0, and 2.0 kHz. This masking effect varied between 4.8 and 7.3 dB at those frequencies. No significant masking was measured at a masking level of 115 dB re 1 μPa. The available data indicate that the potential masking effect would be limited to short ranges in the open sea, but limitations exist to this conclusion and all estimates are based on existing turbine types, not taking into account future developments of larger and potentially noisier turbine types.

Figure 1. Map of the Indo-Pacific region showing localities of specimens analysed in the study; EA: Eastern Australia, NA: Northern Australia, SF: South-east Africa, CS: East and South China Seas, SA: Southern Australia.  
Figure 2. Graph and histograms of body and skull lengths of T. cf. aduncus and T. truncatus.  individual specimens for which both body length and skull length were obtained are plotted as discrete points on the graph. Means for all skull and body lengths, for each region, are also plotted; Eastern Australia, Northern Australia, South-eastern Africa and the East and South China Seas (see Table 1). Histograms show all body (top) and skull (right) lengths obtained for T. truncatus and T. cf. aduncus from Eastern Australia, Northern Australia, South-east Africa and the East and South China Seas.
Figure 3. Photographs of T. truncatus and T. cf. aduncus showing the dorsal cape, which in T. truncatus has a distinct blaze lateral to the dorsal fin. A: T. cf. aduncus off the south-east Queensland coast, B: T. cf. aduncus in Moreton Bay, C: T. cf. aduncus from the south-eastern Queensland coast at Sea World Oceanarium (note ventral spotting), D: T. truncatus from the south-east Queensland coast at Sea World Oceanarium, E and F: T. truncatus in Hervey Bay. Refer to Fig. 4 for localities.  
Figure 4. Distribution of T. truncatus and T. cf. aduncus identified during boat searches. A: Australia and the study area on the east coast over which T. truncatus and T. cf. aduncus were identified; B: Moreton Bay, adjacent to Brisbane, and nearby oceanic waters. Dotted line is the 30-m depth contour; C: Hervey Bay and the northern part of the Great Sandy Strait (GSS). Shading denotes the general area of searches, triangles are positions of pods of T. cf. aduncus, circles are positions of pods of T. truncatus.
Comparative morphology and distribution of the aduncus and truncatus forms of bottlenose dolphin Tursiops in the Indian and Western Pacific Ocean

January 2000


880 Reads

Two morphological forms of the bottlenose dolphin, Tursiops truncatus, are recognised in Indo-Pacific waters; a coastal form referred to as T. cf. aduncus and an offshore form, T. truncatus. The two are distinguished primarily on the basis of ventral spotting, present in adult T. cf. aduncus and absent in T. truncatus. We compared the morphology of specimens obtained from parts of their range where both forms are found; south-east Africa, the East and South China Seas and eastern Australia. Across its range, T. cf. aduncus has a shorter body and skull length and on average more teeth than T. truncatus from the same areas. No difference in body length was noted between sexes in T. cf. aduncus while male T. truncatus are larger than females. T. cf. aduncus from tropical waters are distinctly smaller than in subtropical / temperate regions. Differences in the pattern of the dorsal cape between forms from eastern Australia enabled their geographic distribution to be investigated. T. cf. aduncus was found in estuarine and near-coastal oceanic waters and T. truncatus in near-coastal oceanic and offshore waters. Differences in morphology, and likely niche separation in this partially sympatric distribution of the two forms suggests two species, but there are arguments both for and against the assignment of species status to each morphotype.

Figure 1. Out-of-water sampling of wild dugongs: A. Dugong with oral temperature probe in left buccal (mouth) cavity and doppler heart detector deployed under sternum to measure resting heart rate; B. Blood sampling from medial surface of left pectoral fin of adult female dugong. Note large axillar nipple; C. Blood sampling from lateral surface of left pectoral fin; and D. Plastic Frisbee ® placed under urinogenital opening to collect urine, and portable image ultrasound transducer used to 
Physiological Response of Wild Dugongs (Dugong dugon) to Out-of-Water Sampling for Health Assessment

January 2010


1,535 Reads

The dugong (Dugong dugon) is a vulnerable marine mammal with large populations living in urban Queensland waters. A mark-recapture program for wild dugongs has been ongoing in southern Queensland since 2001. This program has involved capture and in-water sampling of more than 700 dugongs where animals have been held at the water surface for 5 min to be gene-tagged, measured, and biopsied. In 2008, this program expanded to examine more comprehensively body condition, reproductive status, and the health of wild dugongs in Moreton Bay. Using Sea World’s research vessel, captured dugongs were lifted onto a boat and sampled out-of-water to obtain accurate body weights and morphometrics, collect blood and urine samples for baseline health parameters and hormone profiles, and ultrasound females for pregnancy status. In all, 30 dugongs, including two pregnant females, were sampled over 10 d and restrained on deck for up to 55 min each while biological data were collected. Each of the dugongs had their basic temperature-heart rate-respiration (THR) monitored throughout their period of handling, following protocols developed for the West Indian manatee (Trichechus manatus). This paper reports on the physiological response of captured dugongs during this out-of-water operation as indicated by their vital signs and the suitability of the manatee monitoring protocols to this related sirenian species. A recommendation is made that the range of vital signs of these wild dugongs be used as benchmark criteria of normal parameters for other studies that intend to sample dugongs out-of-water.

Effects of Human Traffic on the Movement Patterns of Hawaiian Spinner Dolphins ( Stenella longirostris ) in Kealakekua Bay, Hawaii

December 2008


808 Reads

Kealakekua Bay is an important resting site for Hawaiian spinner dolphins (Stenella longirostris) and is popular with both local residents and tourists. Human activities occurring here include swimming, snorkeling, kayaking, and motor-boating. The objectives of this study were to document movement patterns of dolphin groups in Kealakekua Bay, to determine if different types and levels of human activity within the bay result in quantifiable changes in dolphin group movement patterns, and to provide baseline data for future studies. Theodolite tracking was used to assess responses of dolphin groups to human traffic. Variables examined included group mean leg speed (leg speed: the distance between two consecutive theodolite fixes of a dolphin group divided by time; mean leg speed: the average of all leg speeds comprising a track) and group reorientation rate. Swimmers and/or vessels were present within 100 m of all dolphin groups tracked during all surveys. Regression analyses were used to examine potential relationships between dolphin group related variables (e.g., reorientation rate, mean leg speed) and variables related to human activities (e.g., swimming, kayaking, motor-boating). Increasing levels of human activity had a limited but measurable effect on the movement patterns of Hawaiian spinner dolphin groups at this site.

A Method for Capturing Dugongs (Dugong dugon) in Open Water

June 2006


1,490 Reads

We developed a method to rapidly and safely live capture wild dugongs based on the “rodeo method” employed to catch marine turtles. This method entails close pursuit of a dugong by boat until it is fatigued. The dugong is then caught around the peduncle region by a catcher leaping off the boat, and the dugong is restrained at the water surface by several people while data are collected. Our sampling protocol involves a short restraint time, typically < 5 min. No ropes or nets were attached to the dugong to avoid the risk of entanglement and subsequent drowning. This method is suitable for shallow, open-water captures when weather and water conditions are fair, and may be adapted for deeper waters.

Sexing Sirenians: Validation of Visual and Molecular Sex Determination in Both Wild Dugongs (Dugong dugon) and Florida Manatees (Trichechus manatus latirostris)

June 2009


878 Reads

Sexing wild marine mammals that show little to no sexual dimorphism is challenging. For sirenians that are difficult to catch or approach closely, molecular sexing from tissue biopsies offers an alternative method to visual discrimination. This paper reports the results of a field study to validate the use of two sexing methods: (1) visual discrimination of sex vs (2) molecular sexing based on a multiplex PCR assay which amplifies the male specific SRY gene and differentiates ZFX and ZFY gametologues. Skin samples from 628 dugongs (Dugong dugon) and 100 Florida manatees (Trichechus manatus latirostris) were analysed and assigned as male or female based on molecular sex. These individuals were also assigned a sex based on either direct observation of the genitalia and/or the association of the individual with a calf Individuals of both species showed 93 to 96% congruence between visual and molecular sexing. For the remaining 4 to 7%, the discrepancies could be explained by human error. To mitigate this error rate, we recommend using both of these robust techniques, with routine inclusion of sex primers into microsatellite panels employed for identity, along with trained field observers and stringent sample handling.

Underwater Sound Detection Thresholds (0.031-80 kHz) of Two California Sea Lions (Zalophus californianus) and a Revised Generic Audiogram for the Species
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September 2023


34 Reads

Unmasked behavioral audiograms of two California sea lions (Zalophus californianus), an adult female (F01) and a subadult male (M02), were recorded using narrow-band frequency-modulated hearing test signals. Signals had a duration of 1 s and center frequencies ranging from 0.031 to 80 kHz. Hearing thresholds were measured by varying test signal amplitude according to the up-down staircase method. The resulting underwater audiograms (50% detection thresholds) of the two sea lions were similar and showed the typical mammalian U-shape. Maximum hearing sensitivity (58 and 57 dB re 1 mPa) occurred at 11.3 kHz for F01 and at 8 kHz for M02, respectively. The range of best hearing (defined as < 10 dB from the maximum sensitivity) was from 1 to 16 kHz (four octaves). The detection thresholds for hearing test signal frequencies 0.031, 0.040, and 0.050 kHz were lower than expected, possibly caused by a shift in perceptional modality from auditory to vibrotactile, or due to the difficulty in measuring accurate SPLs of such low frequencies in a pool. Measurements of particle motion deemed detection of these very low frequencies via the vibrissae unlikely. The present study extends the frequency range for which the hearing of California sea lions has been tested. Based on the two audiograms of the present study and audiograms reported by Reichmuth et al. (2013) and Cunningham & Reichmuth (2016), a revised generic audiogram for California sea lions is proposed.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to One-Sixth-Octave Noise Bands Centered at 0.6 and 1 kHz

May 2022


101 Reads

To determine the frequency-dependent susceptibility of California sea lions (Zalophus californianus) to noise-induced temporary hearing threshold shift (TTS), one of two subjects were exposed for 60 minutes to two continuous one-sixth-octave noise bands (NBs) as fatiguing sounds: one centered at 0.6 kHz, at sound pressure levels (SPLs) of 168 to 174 dB re 1 µPa (sound exposure levels [SELs] of 204 to 210 dB re 1 µPa2s), or one centered at 1 kHz, at SPLs of 144 to 159 dB re 1 µPa (SELs of 180 to 195 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at 0.6, 0.85, 1, 1.2, 1.4, and 2 kHz (at the center frequency of each NB, half an octave higher, and one octave higher). When significant TTS occurred, higher SELs resulted in greater TTSs. In the sea lion that was tested 1 to 4 minutes after exposure to the fatiguing sounds, the largest TTSs occurred when the hearing test frequency was half an octave higher than the center frequency of the two fatiguing sounds. The highest TTS levels elicited were 8.7 dB at 0.85 kHz and 9.6 dB at 1.4 kHz. When their hearing was tested at the same time after the fatiguing sounds stopped, initial TTSs and hearing recovery patterns were similar in both sea lions. These findings will contribute to the protection of hearing of species in the Otariidae family from anthropogenic noise by facilitating the development of an evidence-based underwater sound weighting function.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to One-Sixth-Octave Noise Bands Centered at 8 and 16 kHz: Effect of Duty Cycle and Testing the Equal-Energy Hypothesis

January 2022


116 Reads

To determine the frequency-dependent susceptibility of California sea lions (Zalophus californianus) to noise-induced temporary hearing threshold shift (TTS), two subjects were exposed for 60 min to two fatiguing sounds: continuous one-sixth-octave noise bands (NBs) centered at 8 kHz (at sound exposure levels [SELs] of 166 to 190 dB re 1 µPa2s) and at 16 kHz (at SELs of 183 to 207 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at 8, 11.3, 16, 22.4, and 32 kHz (at the center frequency of each NB, half an octave higher, and one octave higher). For both NBs, higher SELs resulted in greater TTSs. In the SEL ranges that were tested, the largest TTSs occurred when the hearing test frequency was half an octave higher than the frequency of the fatiguing sound. When their hearing was tested at the same time after the fatiguing sounds stopped, initial TTSs and hearing recovery patterns were similar in both sea lions. The effect of fatiguing sound duty cycle on TTS was investigated with the 8 kHz NB, using 1,600 ms signals at a mean sound pressure level (SPL) of 154 dB re 1 µPa. Duty cycle reduction from 100 to 90% resulted in a large decrease in TTS; no TTS was observed at duty cycles ≤ 30%. The equal-energy hypothesis was tested with the 8 kHz NB and found to hold true: five combinations of SPL and exposure duration all resulting in a 182 dB SEL produced similar initial TTSs in both sea lions. These findings will contribute to the protection of otariid hearing from anthropogenic noise by facilitating the development of evidence-based underwater sound weighting functions. Our results also show that the introduction of short inter-pulse intervals to underwater sounds aids in the protection of otariid hearing by allowing recovery to take place.

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