An overview of research efforts to understand the effects of underwater sound on cetaceans

Cetaceans are aquatic mammals living in an environment that is more suited for hearing than vision.As such,their sensory systems largely utilize acoustic cues for navigation,communication,foraging,and predator avoidance.However,the elevation of underwater sound levels from increased human activities has adversely affected cetaceans’use of sound to perform vital life functions.To address those impacts,scientific studies have been conducted to understand the behavioral,psychoacoustical,physiological,and physical responses by cetaceans that have been exposed to anthropogenic sound.These studies range from captive experiments involving auditory thresholds and noise-induced threshold shifts,to field observations of behavioral disturbance from sound exposure,to post-mortem examinations of physical manifestations in stranded animals.Over the years,results from these studies have assisted regulatory agencies in developing a series of criteria and thresholds for cetacean conservation and management around the world.This paper provides a high-level overview of worldwide research efforts that have been dedicated to understanding the effects of underwater sound on cetaceans.The review is not intended to be exhaustive but rather to capture major efforts and significant findings in this field.In addition,the review excludes synthesis studies and modeling exercises that do not involve direct research on target species.

A pioneering survey of deep-diving and off-shore cetaceans in the northern South China Sea

A pioneering boat-based survey was conducted in 2019,to gather baseline information regarding the presence,composition,relative abundance,and spatial distribution of deep-diving and off-shore cetaceans in the northern South China Sea(SCS).A total of 27 sightings comprising at least 8 cetacean species were recorded during the 13-day survey,including 5 deep-diving species(i.e.Risso’s dolphin[Grampus griseus],short-finned pilot whale[Globicephala macrorhynchus],sperm whale[Physeter macrocephalus],Cuvier’s beaked whale[Ziphius cavirostris],and an unidentified beaked whale[either the ginkgo-toothed beaked whale,Mesoplodon ginkgodens,or Deraniyagala’s beaked whale,Mesoplodon hotaula]),as well as 3 off-shore dolphins(i.e.pantropical spotted dolphin[Stenella attenuate],striped dolphin[Stenella coeruleoalba],and Fraser’s dolphin[Lagenodelphis hosei]).With the exception of pantropical spotted dolphins,all other species were sighted and recorded at sea in the northern SCS for the first time.The pantropical spotted dolphin was the most frequently sighted species,comprising 30%of the total sightings.Deep-diving cetaceans were mainly sighted in the northern Xisha Archipelago,whereas off-shore dolphins were distributed across the survey area.The pantropical spotted dolphin was observed in aggregations of more than 100 individuals and nearly all encountered species included calves;these findings suggested that the survey area functions as an important feeding and calving ground for various cetacean species.This pioneering survey provides fundamental information regarding cetacean fauna in the northern SCS and highlights the need to strengthen research and conservation efforts concerning these species.

Annotated checklist and fisheries interactions of cetaceans in Togo, with evidence of Antarctic minke whale in the Gulf of Guinea

Based on strandings and captures,9 cetacean species,including 6 odontocetes and 3 mysticetes,are document-ed(photos and specimens)in Togo’s coastal waters(newly-recorded species marked with an asterisk):Antarc-tic minke whale(Balaenoptera bonaerensis*),Bryde’s whale(Balaenoptera brydei or B.edeni),humpback whale(Megaptera novaeangliae),sperm whale(Physeter macrocephalus),pygmy sperm whale(Kogia brevi-ceps*),short-finned pilot whale(Globicephala macrorhynchus*),pantropical spotted dolphin(Stenella attenu-ata*),common bottlenose dolphin(Tursiops truncatus)and common dolphin Delphinus sp.An anecdotal sight-ing record for killer whale(Orcinus orca)is considered reliable.The lack of Sousa teuszii records in Togo is consistent with its apparent contemporaneous absence in Ghana.The B.bonaerensis specimen,entangled in a purse seine set on small pelagics,is a first record for the Gulf of Guinea.The occurrence of this Southern Ocean species north of the equator underscores the severe gaps in our understanding of cetacean distribution off west-ern Africa.The majority of artisanal fishermen operating in Togolese coastal waters are of Ghanaian origin and are thought to promote trade and consumption of cetacean bushmeat.Because captures are illegal,enforced with some success in the main fishing centers,covert landings of cetaceans are exceedingly difficult to moni-tor,quantify or sample.Concern is expressed about pollution of Togo’s coastal waters with heavy metals due to phosphorite mining and export from the coastal basin near Hahotoéand Kpogamé.

Long-term study of at-sea distribution of seabirds and marine mammals in the Scotia Sea, Antarctica

The Scotia Sea is one of the most biologically rich regions of Antarctica, and it hosts a large community of upper trophic-level predators. Long-term at-sea monitoring provides valuable information on the Antarctic marine ecosystem and relationships among top predators. This paper presents the results of at-sea monitoring of seabirds and cetaceans over five consecutive summer seasons （2010--2014） in the Scotia Sea, Antarctica. A total of 11 656 flying birds belonging to 24 species were recorded in 884 ten-minute counts. Six Procellariiformes species were abundant： Black-browed Albatross, Cape Petrel, Southern Fulmar, Antarctic Prion, Wilson＇s Storm-petrel, and Black-bellied Storm-petrel. Only three of these species accounted for 82% of the total abundance： Antarctic Prion （40%）, Southern Fulmar （22%）, and Cape Petrel （20%）. A total of 678 baleen whales belonging to five species were recorded along a sampling effort of 2 351 nautical miles： Humpback, Sei, Southern Right, Fin, and Minke whales, which had different abundances during the study. The Fin Whale had the highest mean encounter rate for the 5 years （0.29 whales per nautical mile）, followed by the Humpback Whale （0.09 whales per nautical mile）. Annual dissimilarity in abundance of both seabirds and cetaceans occurred in conjunction with changes in the sea surface temperature and ice cover, showing the dependence of top predators on environmental changes. The largest aggregations of all top predators （seabirds and cetaceans） were recorded in two regions, west and south of the South Orkney Islands, suggesting important prey availability （especially krill） in those areas.

Evolutionary impacts of purine metabolism genes on mammalian oxidative stress adaptation

Many mammals risk damage from oxidative stress stemming from frequent dives(i.e., cycles of ischemia/reperfusion and hypoxia/reoxygenation),high altitude and subterranean environments, or powered flight. Purine metabolism is an essential response to oxidative stress, and an imbalance between purine salvage and de novo biosynthesis pathways can generate damaging reactive oxygen species(ROS). Here, we examined the evolution of 117 purine metabolism-related genes to explore the accompanying molecular mechanisms of enhanced purine metabolism in mammals under high oxidative stress. We found that positively selected genes,convergent changes, and nonparallel amino acid substitutions are possibly associated with adaptation to oxidative stress in mammals. In particular, the evolution of convergent genes with c AMP and c GMP regulation roles may protect mammals from oxidative damage. Additionally, 32 genes were identified as under positive selection in cetaceans, including key purine salvage enzymes(i.e., HPRT1), suggesting improved re-utilization of non-recyclable purines avoid hypoxanthine accumulation and reduce oxidative stress. Most intriguingly, we found that six unique substitutions in cetacean xanthine dehydrogenase(XDH), an enzyme that regulates the generation of the ROS precursor xanthine oxidase(XO) during ischemic/hypoxic conditions, show enhanced enzyme activity and thermal stability and diminished XO conversion activity. These functional adaptations are likely beneficial for cetaceans by reducing radical oxygen species production during diving. In summary, our findings offer insights into the molecular and functional evolution of purine metabolism genes in mammalian oxidative stress adaptations.

Contracture Development in Whales

It is well known that whales in captivity suffer from dorsal fin bending. However, the mechanisms behind this change are poorly understood. Humans can suffer from similar symptoms either after a period of immobilization or after suffering a brain lesion. Therefore, we here speculate whether the bent dorsal fins are reflecting contracture development in whales.

Inter-Laboratory Ring Trial to Evaluate Reverse Transcription Polymerase Chain Reaction Methods Used for <i>Dolphin Morbillivirus</i>Detection in Italy

Dolphin Morbillivirus (DMV) is one of the most frequently detected pathogens in stranded cetacean specimens worldwide as well as in Italy. Due to the persistence of DMV in the Mediterranean Sea and to the lack of information about the efficiency of the available diagnostic techniques, the Italian National Reference Centre for diagnostic activities on dead stranded marine mammals (C.Re.Di.Ma) performed the first inter-laboratory ring trial with the aim to standardize a diagnostic biomolecular approach for DMV in Italy. Viral isolation is usually considered the “gold standard” for the definitive diagnosis of most pathogens, but it is not often feasible in DMV diagnosis, due to the poor preservation of virus-targeted tissues in stranded cetacean carcasses, as well as to the lack of appropriate sensitivity of cell lines towards DMV variability. Therefore direct viral detection on tissues by means of reverse transcription-PCR (RT-PCR) represents a valuable option for DMV infection’s diagnosis. For detecting DMV in cetacean die-offs occurred in the Mediterranean basin since 2013, C.Re.Di.Ma developed an RT-PCR based method targeting to a 287 bp fragment of DMV nucleoprotein (N) gene. With the purpose to evaluate its performances in terms of accuracy (Se = sensitivity and Sp = specificity) and precision (reproducibility), it was submitted to a ring trial. So, 12 Public Laboratories belonging to the Italian dead stranded marine mammals diagnostic network were asked to analyze a panel of 40 samples (positive and negative for DMV, using different dilutions of a viral suspension obtained from a cell culture supernatant of a DMV strain) with the aforementioned technique. Furthermore, we also aimed at comparing the accuracy of other 7 molecular methods routinely applied for DMV detection in Italy. For this purpose, the second panel of identical 40 DMV +ve and -ve samples was provided to Laboratories that routinely used DMV detection methods other than those developed by C.Re.Di.Ma, in order to be analyzed simultaneously with the method they usually applied. The C.Re.Di.Ma technique showed high accuracy [mean Se = 97.8% (95% CI 84.2% - 99.3%), mean Sp = 98.1% (95% CI 72.5% - 99.9%)] and very good precision [k combined equal to 0.91 (95% CI 0.87 - 0.95)]. In conclusion, this study highlighted a satisfactory reliability of most of the molecular methods used in Italy for DMV detection.

An Assessment of the Marine Mammal Abundance and Population Density within the Ghanaian Offshore Construction Areas

The Gulf of Guinea region enjoined with the unique characteristics of the Guinea surface and underwater currents driving the upwelling season, besets the ecological importance of the area amidst growing offshore development. Though several attempts are being made to identify the various cetacean species inhabiting the area, little to no progress is made to under the animal population, their behaviour and distribution in the face of the growing threat. The study hence attempts to develop cetacean population and distribution estimation within Ghana’s offshore construction sites in the time frame of field development while emphasizing the effects of operations on animal behaviour and habitats, purpose at providing an understanding with the general behaviour of these mammals peculiar to the area and too what level the impact of change is having on distribution trends. The study finds the upwelling tends to suggest, strong animal presence in the area during feeding. Short-fin pilot whales were a dominant cetacean feature within the observed cetacean population estimated to have 160 (CV = 0.3728) presence. Findings suggest the strong biological importance, BIA (habitat, feeding and breeding), as well as operations drawing on animal curiosity, heightened animal vulnerability. Further studies are required to understand the temporal and spatial distributions patterns, while efforts are needed to ensure protected areas are established, animal surveillance and conservative attitudes are encouraged.

An overview of cetacean strandings, bycatches and rescues along the western coast of the Taiwan Strait, China: 2010–2015

The analysis of cetacean strandings can provide fundamental information about species diversity and composition in a particular region. The present study collected and analyzed cetacean strandings, bycatches and rescues along the western coast of the Taiwan Strait, China, from 2010 to 2015. In total, 48 records, including 37 strandings, 8 bycatches and 3 rescues, involving 13 known species were collected. Among them, Indo-Pacific humpback dolphins（Sousa chinensis） and finless porpoises（Neophocaena phocaenoides） were the most common species, consisting of 31.3% and 25%, respectively. Notably, 10 out of the 48（20.8%） records were collected from the Pingtan Island and included 3 species of Mysticeti and 4 species of Odontoceti. Finally, we compared the cetacean species composition between the western and eastern coasts of the Taiwan Strait; 31 cetacean species occurred in the Taiwan Strait, indicating a relatively high cetacean diversity in this region. Systematic field surveys are urgently needed to explore the cetacean species composition, population stock and the related habitat status in the Taiwan Strait, which may improve conservation management in the future.

Towards a Standardized Approach of Cetacean Habitat: Past Achievements and Future Directions

The understanding of what habitat means for an organism as well as the underlying factors driving patterns of habitat use is still unknown for many species. Cetacean habitat has been described using a range of methodologies and variables measured over various temporal and spatial scales?that are often author-dependent. However, in order to develop an objective and sound understanding of what habitat actually means for cetaceans, a standardized approach needs to be developed. Here, after briefly reviewing the fundamental differences between terrestrial and marine habitats, we highlight the difficulty in defining a marine habitat, with a special focus on marine mammals. We subsequently provide six recommendations by which future cetacean habitat studies might be approached. This recommended approach aims to amend the way in which we think about and undertake investigations into cetacean habitat. It is believed that through this broadened approach, future cetacean habitat studies will increase our understanding of underlying driving factors of cetacean habitat, rather than just describing distribution patterns. Finally, it is stressed how the proposed approach will be more directly applicable within management frameworks and of benefit to conservation initiatives.

The rough-toothed dolphin genome provides new insights into the genetic mechanism of its rough teeth

The rough-toothed dolphin(Steno bredanensis)is characterized by having teeth covered infinely wrinkled vertical ridges,which is a general manifestation of amelogenesis imperfecta.The rough surfaces are hypothesized to be an evolutionary morphological trait of feeding adaptation to increase the dolphin’s grip on prey.Here,we assembled a rough-toothed dolphin genome and performed the comparative genomic analysis to reveal the genetic basis of the special enamel.Results showed that genes related to enamel development or dental diseases have undergone diver-sified adaptive changes that may shape the special enamel morphology of this dolphin species,including positive selection(CLDN19,PRKCE,SSUH2,and WDR72),rapid evolution(LAMB3),or unique amino acid substitutions(AMTN,ENAM,MMP20,and KLK4).Meanwhile,the historical demography of rough-toothed dolphin indicated several distinct populationfluctuations associated with climate change.The genome-wide heterozygosity of this dolphin is in the middle of all published data for cetaceans.Although the population is considerable,there may be population or subspecies differentiation,and with the global warming and the increasing disturbance of human activities,we should pay more attention to protection in the future.Together,our study brings new insights into the genetic mechanisms that may have driven the evolution of the special enamel morphology in rough-toothed dolphins and provides thefirst results of genetic heterozygosity and population historical dynamics of this species,which have important guiding implications for the conservation of this dolphin species.

Cetacean occurrence and diversity in whale-watching waters off Mirissa,Southern Sri Lanka

Scientific information is vital to the conservation of cetaceans and the management of whale-watching activities.The southern coastal waters of Sri Lanka are near a narrow continental shelf and biologically abundant in cetacean species.Although the occurrence of cetaceans has been investigated in certain waters of Sri Lanka,few surveys have been conducted along the southern coast.To fill this gap,we conducted boat-based surveys from January to May 2017 to investigate the occurrence,diversity,and behavior of cetaceans in the waters off Mirissa,covering a survey area of 788.9 km2.During 55 survey days,we recorded a total of 242 cetacean sightings and identified at least 9 species(3 mysticetes and 6 odontocetes).The blue whale was the most common mysticete species(167 of 174 mysticete encounters),followed by the Omura’s whale(4 of 174)and Bryde’s whale(3 of 174).The spinner dolphin was the most common odontocete species(28 of 68 odontocete encounters),followed by the sperm whale(18 of 68),common bottlenose dolphin(13 of 68),short-finned pilot whale(5 of 68),melon-headed whale(2 of 68),and killer whale.Blue whales and sperm whales exhibited a clear preference for outer shelf and high slope areas,and blue whales were observed feeding along these waters.The present study provides near-baseline information on cetacean occurrence and diversity in whale-watching waters off southern Sri Lanka,and highlights the urgent need for proper management strategies for whale-watching activities.

The intestinal microbiome of an Indo-Pacific humpback dolphin(Sousa chinensis)stranded near the Pearl River Estuary,China

The mammalian intestinal microbiome is critical for host health and disease resistance.However,the cetacean intestinal microbiota remains relatively unexplored.By using high-throughput 16S rRNA gene sequencing,we analyzed intestinal bacterial samples from an Indo-pacific humpback dolphin(Sousa chinensis)stranded near the Pearl River Estuary in China.The samples included 3 anatomical regions(foregut,midgut,and rectum)and 2 anatomical locations(content and mucus).Our analyses revealed that the dolphin intestinal bacteria contained 139 operational taxonomic units(OTUs),dominated at the phyla level by Firmicutes(47.05%in the content;94.77%in the mucus),followed by Bacteroidetes(23.63%in the content;1.58%in the mucus)and Gammaproteobacteria(14.82%in the content;2.05%in the mucus).The intestinal bacteria had a small core community(15 OTUs,accounting for 99.74%of the reads),some of which could be potentially pathogenic to both human and dolphins.As an alternative to sampling the dolphin intestinal bacteria,fecal sampling could be used.Additionally,function potentials such as,xenobiotics biodegradation,beta-lactam resistance,and human disease-related pathways,were detected in the dolphin intestinal bacteria.These findings provide the first baseline knowledge of the intestinal microbiome of the Indo-Pacific humpback dolphin,which may offer new insights into cetacean conservation by using microbial surveillance.

Cetacean morbillivirus: A Land-to-Sea Journey and Back?

Cetacean morbillivirus(CeMV),the most relevant pathogen impacting the health and conservation of several already threatened cetacean populations worldwide(Van Bressem et al.2014),has shown in recent years an apparently increased tendency to cross"interspecies barriers"(Jo et al.2018a),thereby giving rise to disease and mortality outbreaks in free-ranging dolphins and whales(Mazzariol et al.2016,2017;Jo et al.2018b).

Sexual maturity,seasonal estrus,and gestation in female Indo-Pacific bottlenose dolphins Tursiops aduncus inferred from serum reproductive hormones

Reproductive hormones in serum concentrations of progesterone,estradiol,and testosterone in female Indo-Pacific bottlenose dolphins(Tursiops aduncus,n=12)housed in Ocean Park Hong Kong were investigated in the present study.Results showed that,onset of puberty of captive Indo-Pacific bottlenose dolphins was at 5 years while sexual maturity was at 6.Average serum progesterone concentrations in non-pregnant sexually mature individuals was 0.33(0.25–0.97)ng/mL(interquartile),significantly higher than in immature ones 0.26(0.25–0.38)ng/mL.This study found significant difference in serum estradiol concentrations between individuals at the onset of puberty(9.5±1.7 ng/mL,±SD)and not(below detection limit 9 pg/mL).A slightly seasonal breeding pattern,with progesterone values tend to be higher from February to October(0.38[0.25–1.07]ng/mL)was inferred.During pregnancy,serum progesterone concentrations range from 10.54±8.74 ng/mL(indexed month post-conception[IMPC]0)to 25.49±12.06 ng/mL(IMPC 2),and display a bimodal pattern with 2 peaks in early-(25.49±12.06 ng/mL,IMPC 2)and late-pregnancy(21.71±10.25 ng/mL,IMPC 12),respectively.Serum estradiol concentrations can seldom be detected in early-pregnancy and increase constantly in mid-(9.45±1.83 pg/mL)and late-pregnancy(11.88±3.81 pg/mL),with a spike(15.45±6.78 pg/mL)1 month prior to delivery.Serum testosterone concentrations elevate significantly in IMPC 7(0.36±0.10 ng/mL)compared to other months(0.16±0.10 ng/mL)of the year.The present study provides normal concentration profiles for some reproductive hormones in female Indo-Pacific bottlenose dolphins and can contribute to the breeding monitoring of this species.Also,our study would shed further light on the reproductive physiology of small cetaceans.