Sperm whales in the waters off China:A glimpse of the past and present

Spatiotemporal information is crucial for cetacean research and conservation,particularly for wide-ranging and migratory species.Sperm whales(Physeter macrocephalus)are distributed worldwide in deep oceans;however,little is known about the species in the western margin of the Pacific Ocean.Here,we examined the available information related to the occurrence,distribution,and potential habitats of sperm whales in the waters off China.Historical whaling information(18th–20th century)indicates that sperm whales have been captured in the East China Sea(ECS)and South China Sea(SCS).Furthermore,sporadic strandings have been recorded since the 1910s,and more frequently from 1990 onwards.Since 1990,accidental sightings have been documented in the eastern ECS,northeastern and southern SCS,and their adjacent waters.More recently(2019–2022),field encounters have been reported in dedicated ship-based investigations in the Xisha and Nansha waters,providing robust evidence of the regular existence and potential residency of sperm whales in the northwestern and central areas of the SCS.Female nursery groups suggest that the Xisha waters might be an important nursing ground for sperm whales.Satellite tracking data from four adults showed that sperm whales in the SCS might display both fine-scale and long-distance movements.Taken together,it appears that sperm whales are currently active in the waters off China,and that deep waters(depth>200 m)in the ECS and SCS may provide the species with critical habitats.This review provides crucial baseline information on sperm whales in the waters off China,which may help to facilitate future research efforts and conservation initiatives for the species at national and cross-regional scales.More field investigations and other monitoring approaches including acoustic monitoring,biologging,photo-identification,and genetics are required to reveal the distribution,movement,and habitat use patterns of sperm whales in these waters.

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.

First live sighting of Deraniyagala’s beaked whale(Mesoplodon hotaula)or ginkgo-toothed beaked whale(Mesoplodon ginkgodens)in the western Pacific(South China Sea)with preliminary data on coloration,natural markings,and surfacing patterns

Beaked whales represent around 25%of known extant cetacean species,yet they are the least known of all marine mammals.Identification of many Mesoplodon species has relied on examination of a few stranded individuals.Particularly,the ginkgo-toothed beaked whale(Mesoplodon ginkgodens)and Deraniyagala’s beaked whale(Mesoplodon hotaula)are among the least-known of beaked whale species,without confirmed sightings of living individuals to date.We present a sighting of 3 free-ranging individuals of M.ginkgodens/hotaula whale from a dedicated marine mammal vessel survey carried out in the South China Sea in April and May 2019.Photographic data(301 photographs)from the sighting were compared to photos of fresh stranded ginkgo-toothed beaked whale and Deraniyagala’s beaked whale from both historical and unpublished records.We found that free-ranging M.ginkgodens and M.hotaula individuals can be easily distinguished from other Mesoplodon species due to differences in melon and gape shapes and coloration patterns.However,accurate at-sea differentiation of M.ginkgodens and M.hotaula may not be possible due to high similarity in both coloration and scarring patterns.In addition to our photo-identification data,we collected what we believe to be the first preliminary descriptions of surfacing behavior and diving patterns of one of these species.Finally,the presence of scars possibly caused by fishing gear or marine litter raises concerns about anthropogenic impacts and conservation of these poorly known 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.

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.

Temporal variation of the underwater soundscape in Jiaotou Bay,an Indo-Pacific humpback dolphin(Sousa chinensis)habitat off Hainan Island,China

The underwater soundscape is an important ecological element affecting numerous aquatic animals,in particular dolphins,which must identify salient cues from ambient ocean noise.In this study,temporal variations in the soundscape of Jiaotou Bay were monitored from February 2016 to January 2017,where a population of Indo-Pacific humpback dolphins(Sousa chinensis)has recently been a regular sighting.An autonomous acoustic recorder was deployed in shallow waters,and 1/3-octave band sound pressure levels(SPLs)were calculated with central frequencies ranging from 25 Hz to 40 kHz,then were grouped into 3 subdivided bands via cluster analysis.SPLs at each major band showed significant differences on a diel,fishing-related period,seasonal,and tidal phase scale.Anthropogenic noise generated by passing ships and underwater explosions were recorded in the study area.The fish and dolphin acoustic activities both exhibited diel and seasonal variations,but no tidal cycle patterns.A negative significant relationship between anthropogenic sound detection rates and dolphin detection rates were observed,and fish detection rates showed no effect on dolphin detection rates,indicating anthropogenic activity avoidance and no forced foraging in dolphins in the study area.The results provide fundamental insight into the acoustic dynamics of an important Indo-Pacific humpback dolphin habitat within a coastal area affected by a rapid increase in human activity,and demonstrate the need to protect animal habitat from anthropogenic noises.

Research on whales,dolphins,and porpoises

INTRODUCTION This special issue of Integrative Zoology(the official journal of the International Society of Zoological Sciences and the Institute of Zoology,Chinese Academy of Sciences)presents recent research progress on whales,dolphins,and porpoises,with focus on those in relatively less investigated waters,such as waters off China,Sri Lanka,and Chile.In this issue,we showed the use of diverse research methods,analytical technologies,and multi-disciplinary tools,with involvement of both large whales,such as the blue whale(Balaenoptera musculus).

Learning from the heaviest ancient whale

A groundbreaking study published in Nature by Bianucci et al.has reported the discovery of a new basilosaurid species,Perucetus colossus(Figure 1).The incomplete fossil skeleton found in Peru is around 39 million years old.This ancient whale challenges the long-held belief that the blue whale represents the largest known animal to have ever lived on Earth.P.colossus is estimated to have had a body mass between 85 and 340 tons,with an average of 180 tons.1 In comparison,extant blue whales have an estimated body mass of 100–150 tons.The new study proposes that P.colossus was adapted to a fully aquatic lifestyle in shallow water with slow swimming speeds,similar to extant manatees.Elevated bone mass would have aided buoyancy control while diving to shallow depths,as seen in modern-day sirenians.This new discovery not only challenges our understanding of mammalian maximum body mass evolution,but it also expands our knowledge of the lifestyle of ancient cetaceans.

Mapping the fishing intensity in the coastal waters off Guangdong province, China through AIS data

Fishing activities result in a depletion of fish resources and an increase in bycatch probability of non-target species,which are thought to be the cause of the recent demographic change experienced by coastal cetaceans in waters off Guangdong province,China.However,fishing intensity and its spatiotemporal pattern remain poorly examined in this region.Here,random daily tracks from 100 fishing vessels were used to estimate fishing operations in the coastal waters off Guangdong province.The performance of two methods was tested with Automatic Identification System(AIS)data collected in the Pearl River Delta region(PRD).This assessment found that the Density-Based Spatial Clustering of Applications with Noise(DBSCAN)could falsely identify port regions as fishing grounds,while the speed-based method provided a more accurate estimate of fishing grounds with less computational effort.Subsequently,the spatiotemporal pattern of fishing intensity in the coastal waters off the entire Guangdong province was examined with the speed-based method.Our results showed that 87.75%of the coastal fishing activities occurred in waters<40 m in depth.The method detected two spatially heterogeneous fishing grounds extending from the PRD to either the west or east sides of Guangdong province.In the west fishing ground,43.4%of fishing vessels operated in the waters off Yangjiang city;while in the east fishing ground,fishing activities were more evenly distributed.The present study suggests that the AIS is able to provide high-resolution data to monitor the development of fishing activities,which may be useful for informing marine resource management and spatial planning.

Novel insights into the spatial genetic patterns of the finless porpoise from East to Southeast Asia

Several cetacean species are endemically distributed throughout the Indo-Pacific.Due to disproportionate sampling and research efforts across the Indo-Pacific region,the spatial genetic structure of these species remains poorly understood.This has led to poor phylogeographic knowledge and ambiguous taxonomic classification of many Indo-Pacific cetacean species.Of these,the finless porpoise(genus Neophocaena)is a small cetacean obligatory to the inshore waters from East Asia to the Persian Gulf of the Indian Ocean.To date,two species are generally recognized:the narrow-ridged finless porpoise inhabiting temperate and subtropical waters,and wideridged finless porpoises inhabiting subtropical and tropical waters.Early research efforts focused on the temperate waters off the northern China.However,recent studies have proposed that the primary divergence within the genus may lie between the Indian Ocean and Pacific region,which remains to be tested with more samples from tropical and subtropical regions.Here,we examined the genetic relationship among the finless porpoises from the Gulf of Thailand to the Taiwan Strait using both mitochondrial and autosomal markers.Bayesian assignment analysis suggested a minimum of four genetic populations within the study areas,corresponding to the narrowridged finless porpoise from the Taiwan Strait(TWSn),and the three wide-ridged finless porpoise populations from the Taiwan Strait(TWSw),Pearl River Delta region(PRDw),and the Gulf of Thailand(Thaiw),respectively.The minimum spanning network of the mtDNA control region found shared haplotypes among finless porpoises in Chinese waters,but those from the Gulf of Thailand formed a unique matriline lineage.Consistently,the genetic differentiation or divergence within the South China Sea(Thaiw vs.PRDw)appears to be higher than that of most finless porpoise populations examined to date,and meets the threshold values of species or sub-species level proposed for the cetacean species.The Mantel test detected a strong correlation between the geographic and genetic matrices within the South China Sea(r>0.99,p<0.001),indicating that the divergence associated with isolation-by-distance(IBD)has been accumulating in recent history.Our results imply that the formation and maintenance of the spatial genetic pattern of the finless porpoise is more complex than previously thought.However,this cannot be addressed by the current taxonomic classification of the genus.

Prey decline leads to diet shift in the largest population of Indo-Pacific humpback dolphins?

The Pearl River Delta(PRD)region on the southeast coast of China has long been known as a highly productive fishing ground.Since the late 1980s,fishing pressure in the PRD has been intense,which warrants concerns of potential fishery-related impacts on the food resources and foraging ecology of apex marine predators in this region,such as the Indo-Pacific humpback dolphin(Sousa chinensis).In this study,we examined 54 stomachs with food remains,collected from beached carcasses of humpback dolphins recovered during fifteen years between 2003 and 2017.The 6043 identified prey items represent 62 teleost taxa,primarily small estuarine fish,but also larger reef fish.The dolphins appear to be opportunistic foragers,hunting across the water-column,with preference for shoaling and meaty fishes(e.g.Collichthys lucidus IRI%=38.6%,Johnius belangerii IRI%=23.1%,Mugil cephalus IRI%=14.0%).Our findings suggest a dietary shift in recent years,from primarily demersal(as previously reported)to greater intake of neritic and pelagic fish.Dolphin foraging group size has decreased in recent years,which corresponds with declining size and numbers of prey items retrieved from dolphin stomachs.We suggest that these are indicators of declining food resources.Faced with a shortage of preferred prey,humpback dolphins may have broadened their dietary spectrum to maintain their daily energy intake,while their foraging group size decreased in response to the altered tradeoff between the costs and benefits of group foraging.

The biogeography of group sizes in humpback dolphins(Sousa spp.)

Humpback dolphins(Sousa spp.)are obligate shallow-water and resident species,and they typically live in fission–fusion societies composed of small-sized groups with changeable membership.However,we have scant knowledge of their behavioral ecology,starting with potential factors influencing inter-population variability of their group sizes.Here,we compiled a new global dataset of humpback dolphin group sizes based on 150 published records.Our data indicated an inter-specific consistency of group-living strategy among the 4 species in the Sousa genus,as these species preferred living in small-sized groups with a mean size of mostly no more than 10,a minimum size of single individual or small pairs,and a maximum size of several tens or≈100.In addition,we clearly showed the geographic variations in group sizes of humpback dolphins at a global scale.We found that the geographic variations in humpback dolphin group sizes were primarily associated with the latitude,sea surface temperature,and abundance.To conclude,our findings provide insights into social dynamics and socioecological trade-offs of humpback dolphins,and help better understand how these resident animals adapted to their shallow-water habitats from the perspectives of biogeography and socioecology.

Diel differences in blue whale(Balaenoptera musculus)dive behavior increase nighttime risk of ship strikes in northern Chilean Patagonia

The northern Chilean Patagonia region is a key feeding ground and a nursing habitat in the southern hemisphere for blue whales(Balaenoptera musculus).From 2014 to 2019,during 6 separate research cruises,the dive behavior of 28 individual blue whales was investigated using bio-logging tags(DTAGs),generating≈190 h of data.Whales dove to significantly greater depths during the day compared to nighttime(day:32.6±18.7 m;night:6.2±2.7 m;P<0.01).During the night,most time was spent close to the surface(86%±9.4%;P<0.01)and at depths of less than 12 m.From 2016 to 2019,active acoustics(scientific echosounders)were used to record prey(euphausiids)density and distribution simultaneously with whale diving data.Tagged whales appeared to perform dives relative to the vertical migration of prey during the day.The association between diurnal prey migration and shallow nighttime dive behavior suggests that blue whales are at increased risk of ship collisions during periods of darkness since the estimated maximum ship draft of vessels operating in the region is also≈12 m.In recent decades,northern Chilean Patagonia has seen a large increase in marine traffic due to a boom in salmon aquaculture and the passenger ship industry.Vessel strike risks for large whales are likely underestimated in this region.Results reported in this study may be valuable for policy and mitigation decisions regarding conservation of the endangered blue whale.

Modes of genetic adaptations underlying functional innovations in the rumen

The rumen is the hallmark organ of ruminants and hosts a diverse ecosystem of microorganisms that facilitates efficient digestion of plant fibers.We analyzed 897 transcriptomes from three Cetartiodactyla lineages:ruminants,camels and cetaceans,as well as data from ruminant comparative genomics and functional assays to explore the genetic basis of rumen functional innovations.We identified genes with relatively high expression in the rumen,of which many appeared to be recruited from other tissues.These genes show functional enrichment in ketone body metabolism,regulation of microbial community,and epithelium absorption,which are the most prominent biological processes involved in rumen innovations.Several modes of genetic change underlying rumen functional innovations were uncovered,including coding mutations,genes newly evolved,and changes of regulatory elements.We validated that the key ketogenesis rate-limiting gene(HMGCS2)with five ruminant-specific mutations was under positive selection and exhibits higher synthesis activity than those of other mammals.Two newly evolved genes(LYZ1 and DEFB1)are resistant to Gram-positive bacteria and thereby may regulate microbial community equilibrium.Furthermore,we confirmed that the changes of regulatory elements accounted for the majority of rumen gene recruitment.These results greatly improve our understanding of rumen evolution and organ evo-devo in general.

Photo-identification comparison of four Indo-Pacific humpback dolphin populations off southeast China

Indo-Pacific humpback dolphins(Sousa chinensis)inhabit shallow coastal waters of the Indo-Pacific region including southeast China,with at least 6 putative populations identified to date in Chinese waters.However,the connectivity among these populations has not yet been fully investigated.In the present study,we compared and crossmatched photographic catalogs of individual dolphins collected to date in the Pearl River Delta region,Leizhou Bay,Sanniang Bay,and waters southwest of Hainan Island,a total of 3158 individuals,and found no re-sighting of individual dolphins among the 4 study areas.Furthermore,there was a notable difference in the pigmentation pattern displayed by individuals from these 4 regions.We suggest that this may be a phenotypical expression of fine-scale regional differentiation among humpback dolphin groups,possibly distinct populations.Given the considerable conservation management implications it may carry(e.g.definition of management units),further research is much needed.

Blubber fatty acid compositions in different geographic populations of finless porpoise in Chinese waters:implications for thermal adaptation

The stratification of blubber fatty acids(FAs)is a widely used strategy in marine mammals and can be influenced by many factors,including their diet,environmental temperature,and physiological status.There are 3 distinct finless porpoise species/subspecies in Chinese coastal and inland waters in a wide range from 20°N to 40°N.The biochemical stratification of the blubbers of finless porpoises in different regions may provide valuable information for understanding their environmental adaptations.The FA compositions of 4 geographic populations of finless porpoise(FP)collected from the Bohai Gulf,East China Sea,South China Sea,and Yangtze River were therefore analyzed and compared.The blubber FA compositions of finless porpoises were dominated by∑MUFAs,followed by∑SFAs and∑PUFAs,and were generally consistent with those of other cetaceans.The blubber of finless porpoises was significantly stratified with increasing levels of∑MUFAs and decreasing levels of∑SFAs and∑PUFAs from the inner to the outer layers.The 3 marine populations shared more similarities in their FA compositions and stratifications compared to the freshwater porpoises,particularly regarding the PUFAs in the inner layers,which might have been mainly influenced by the diet compositions of marine and freshwater porpoises.Contrary to what was expected,in the 3 marine populations,the SFA and MUFA levels showed opposite correlations(negative and positive,respectively)with habitat temperatures,possibly indicating an adaptation mechanism in finless porpoises characterized by a trade-off between the insulation and fluidity properties of the blubber through the adjustment of the compositions and gradients of MUFAs and SFAs across the blubber depth in response to environmental temperature/latitude changes.