Aquatic Mammals

Online ISSN: 0167-5427
Weight changes of the pup and the weight of the 
The percentage of suckling sessions broken off by the mother and by the pup during each day of the suckling period. 
The total suckling time per day during the suckling period. 
The mother's daily food consumption before, during, and after the suckling period. Triangles indicate days on which no food was offered. 
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.
Schematic overhead view onto research pool and set-up with the animal's position at its underwater station indicated
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.
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).
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.
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.  
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.
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.  
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.
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.
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 
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.
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.
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 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.
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.
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.
Risso’s dolphins (Grampus griseus) were taken for the first time by the opportunistic drive fishery in the Faroe Islands in two separate incidents: three in September 2009 and 21 in April 2010, with in total 16 females and eight males. Their sizes ranged from 193 to 308 cm in length and 60 to 395 kg in weight for females, and 186 to 323 cm in length and 70 to 505 kg in weight for males; the maximum weights are heavier than previously documented for this species. The smallest mature female was 277 cm long, while the youngest and also lightest mature female was 8 y old and weighed 280 kg. Sperm competition and a promiscuous mating system were suggested for the species based on large testicular masses. The diet was composed of cephalopods from both the water column (Todarodes and Loligo) and the ocean floor (Eledona and Todaropsis). Although both schools landed showed a mixed diet, the September school diet centred on a pelagic squid (Todarodes sagittatus), while the April school diet centred upon a benthic octopod (Eledona cirrhosa). Since August 2009, Risso’s dolphins have been observed on five occasions in waters around the Faroese north of 61o 34' N, the northernmost observation situated at a latitude of 62o 23' N. Sightings of the species off Shetland occur mostly between April and September, with a peak in August and September, the observations in Faroese waters (2 in April, 1 in August, and 2 in September) falling within this period. While the species had not previously been observed in this area north of the Shetland-Faroe Channel, these observations in Faroese territorial waters indicate a likely northward extension of the known range of the species.
Information concerning population structure and genetic diversity in Stenella clymene is still scarce. Previous studies raised questions regarding the species' position in the genus Stenella and sug-gested that S. clymene might be of hybrid origin. The present study analyzed the mitochondrial control region (D-loop), cytochrome oxidase I (CoI), and cytochrome b (Cyt b) of northeast-ern Brazil individuals and compared them with S. clymene sequences from the North Atlantic Ocean and Gulf of Mexico. Brazilian individuals showed high haplotype diversity (D-loop: 1.00/p = 0.02; CoI: 0.99/p = 0.04; Cyt b: 0.96/p = 0.06) and probably constitute one population (South Atlantic Ocean). Significant differentiation and high FST values (D-loop: FST = 0.88/p = 0.00; CoI: FST = 0.70/p = 0.00; Cyt b: FST = 0.96/p = 0.00) were found between population units from the North and South Atlantic Ocean. For Cyt b, popu-lation units from the South Atlantic Ocean and Gulf of Mexico showed significant differentia-tion, but the FST value was low (FST = 0.11/p = 0.0). In addition, the haplotype network suggests con-nectivity between South Atlantic Ocean and Gulf of Mexico units. More effort focusing on S. cly-mene is needed to better elucidate the patterns of population structure within this species and, thus, provide sufficient data for conservation strategies.
Map of the study site in southeastern Brazil showing the sub-areas A1, A2, and A3 covered when investing on photo-identification surveys of Guiana dolphins (Sotalia guianensis) between 2015 and 2016
Discovery curve showing the cumulative number of photo-identified Guiana dolphins in the Cananeia estuary during the 55 capture occasions completed between January 2015 and February 2016
Seasonal abundance estimates for the Guiana dolphin population found in the Cananeia estuary between 2015 and 2016, and their associated levels of uncertainty. Dotted and solid lines are estimates for marked and total population size, respectively. Vertical bars indicate the 95% CI.
Summary of survey effort for mark-recapture analysis of Guiana dolphins (Sotalia guianensis) in the Cananeia estuary between 2015 and 2016
Baseline demographic information is essential for effective conservation and management strategies for most living species. The abundance of Guiana dolphins (Sotalia guianensis) is poorly known, yet species conservation is considered a high priority in areas where human activities may induce population declines. This study estimated abundance for Guiana dolphins in the Cananeia estuary (25° 03' S, 47° 55' W) in southeastern Brazil using mark-recapture data and Pollock's Robust Design Model. Systematic boat-based photo-identification surveys were based on data collected in the summer and winter of 2015 and in the summer of 2016. A total of 55 capture events allowed identification of 133 different individuals. The best model indicated a population with random temporary emigration, a time-constant survival rate, and heterogeneous time-varying capture probabilities among primary periods. The temporary emigration rate (γ"= γ') was 0.05 (± 0.03). Estimated population sizes were 430 (95% CI: 410 to 451) individuals in the summer of 2015, 384 (95% CI: 366 to 403) individuals in the winter of 2015, and 414 (95% CI: 392 to 438) individuals in the summer of 2016, indicating that environmental variables among seasons may have a mild effect on the estimated size of this surveyed population. These estimates should stand as an important baseline for future comparisons. Systematic, long-term monitoring of this population is recommended, and is required to accurately assess population trends.
Fish consumption of mother (kg of fish/d) in first week following parturition in Tursiops truncatus (Courtesy of Dolphin Quest)
Handling mom and neonate in shallow water and limited space (Courtesy of Dolphin Quest) 
Animal managers from three institutions that hold Tursiops truncatus participated in a workshop directed at documenting survivability of Tursiops neonates (birth to 30 d of age) in their managed populations. Key information was generated for the period 1990 through 2009 for the three organizations. Included in the findings are (1) documentation of the total live births, total fatalities, and causal factors of neonate losses; (2) recommendations for optimizing animal management procedures through standardized monitoring and husbandry intervention techniques, resulting in the best possible survivability of neonates; and (3) comparison of neonate survivability between the years 1990 to 1999 (78.2% of live births) and 2000 to 2009 (90.6% of live births), the latter decade representing progressing improvements in survivability resulting from recommended animal management procedures.
Although for over two decades resident populations of Mediterranean monk seals (Monachus monachus) have disappeared from Italian locations, sightings of seals have occasionally been reported. The present paper illustrates the methodology used to validate monk seal sightings recorded by third-party observers from 1998 to 2010 and the main results of the validation procedure. The collected monk seal sighting information amounts to 81 observations of which 48 are validated observations corresponding to 35 distinctive sighting events. Over the course of the entire 12-y period, sightings were reported in a somewhat repetitive manner, mostly in the lesser western islands of Sicily and northern Sardinia. The repeated observations over the years in the said areas would suggest that these individuals are not observed incidentally and that there may be a regular use of selected stretches of coast over time. More recently (2009-2010), sightings have also been recorded in the proximity of selected locations of the central-western and northwestern Italian coasts, two of which are characterised by islands. Information on the size class category of the sighted animals, as inferred from the estimated length, suggests that most observed individuals are likely to be juvenile animals, while a smaller amount of seals are likely to be sub-adult and adult-sized individuals. Information from the collected reports indicates that monk seal sightings in Italy, although not frequent, occur steadily and on a repeated basis. Further studies are needed to determine the number of individual monk seals present and their spatial and temporal usage of the coastal areas where they are observed, while awareness activities should be conducted to raise attention to behavioural and reporting procedures to be followed in case of sightings to the benefit of a more thorough monitoring of sightings in the country.
Comparison of the proportion of potential pathogens cultured from Indian River Lagoon (IRL) dolphins between two time periods: 2003-2007 and 2010-2015 (total isolates, N = 733)
Increases in resistance to commonly used antibiotics have been reported globally in isolates from humans, wildlife, and the environment. To date, few studies have examined long-term trends in antibiotic resistance in organisms isolated from marine mammal populations. The objective of this study was to examine temporal trends in resistance to antibiotics among pathogens isolated from common bottlenose dolphins (Tursiops truncatus) between 2003 and 2015. Dolphins were captured and released in the Indian River Lagoon, Florida, an ecosystem with a large coastal human population and significant environmental impacts. Swab samples for microbiology were taken from the blowhole, gastric fluid, and feces and cultured on standard media under aerobic conditions. Isolates were identified using gram stain morphology and growth on selective media. Antibiotic resistance was measured using disc diffusion on Mueller Hinton agar and the Multiple Antibiotic Resistance (MAR) index calculated for each pathogen. A total of 733 isolates was obtained from 171 individual dolphins. The most commonly cultured pathogens included Aeromonas hydrophila, Escherichia coli, Edwardsiella tarda, and Vibrio alginolyticus. The overall prevalence of resistance to at least one antibiotic for the 733 isolates was 88.2%. The MAR index increased significantly between 2003 and 2007 and 2010 and 2015 for Pseudomonas aeruginosa and V. alginolyticus. For all bacterial isolates, resistance to cefotaxime, ceftazidime, and gentamicin increased significantly between sampling periods. This is one of few studies to use the MAR index for bacterial isolates from a marine mammal. The significant increases in resistance for some bacterial species likely reflect shared environmental exposures to antibiotics and transfer of resistance to dolphins from terrestrial sources or from animal or human populations.
The Guadalupe fur seal (Arctocephalus philippii townsendi, Merriam 1897) can now be found on Guadalupe Island and the San Benito Archipelago, off the west coast of the Baja California peninsula. Its population is rising after surviving two periods of intense exploitation during the 19th and 20th centuries. This study estimated the abundance of the Guadalupe fur seal at its main colonies on Guadalupe Island and investigated as to whether there were new colonies on other islands off Baja California. Visual surveys to count Guadalupe fur seals were conducted in 2009 and 2010 around ten islands and archipelagos in the Mexican Pacific. Two sightings were recorded outside the usual distribution range: (1) one juvenile on Todos Santos Island on 11 November 2009 and (2) one subadult male on Asunción Island on 3 June 2010. Differences were found between the fur seal populations counted on Guadalupe Island and the San Benito Islands. From 2009 to 2010, the total minimum counts on Guadalupe Island increased by 30%; while on San Benito, these counts were 50% lower. These fluctuations are presumed to have been caused by animal movements between the two islands, probably due to a northbound migration of this fur seal's prey caused by an El Niño event in 2009 and 2010. The abundance was estimated at 17,581 fur seals on Guadalupe Island in the summer of 2010, and this estimate was obtained by using a correction factor based on the substrate type on the coast and the number of animals not observed during boatbased counts. An abundance of 2,503 animals was recorded on the San Benito Islands.
We report four years (2012-2015) of consecutive observations of the same juvenile male Southern elephant seal along the coast Espírito Santo (ES), Brazil, identified based on scars of cookiecutter shark bites. In 2015 three bacteries were isolated from a recent lesion using routine methods of bacterial culture and identification, and a large number of barnacles were seen attached to the fur of other body regions, especially on the pelvic limbs and lower back. We collected 12 barnacles from different body areas, and identified all of them as Eared barnacles (Conchoderma aurita). Additionally, a sample of feces was obtained and analyzed through simple-flotation, revealing helminth eggs compatible with Contracaecum sp.
Top-cited authors
Ronald Aart Kastelein
Denise Herzing
  • Florida Atlantic University
Paul E Nachtigall
  • University of Hawaiʻi at Mānoa
Brandon Southall
  • University of California, Santa Cruz
Douglas P Nowacek
  • Duke University