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Blubber thickness (BT) has a seasonal pattern in most small cetaceans in temperate and polar regions, which may be a crucial adaptive mechanism in response to environmental temperature changes. However, BT and environmental temperature correlations have never been tested experimentally in any cetacean species owing to logistical difficulties in the aquatic environment. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis, YFP) is one of the smallest cetacean species worldwide, which exclusively inhabits the middle and lower regions of the Yangtze River in China. Here, we investigated BT variation patterns in YFPs and their relationship to environmental temperature changes using ultrasound imaging technology by longitudinally monitoring four YFPs in human care. We found that blubber was not evenly distributed in the skin of YFPs. BT increased along the craniocaudal axis from the head to the umbilical girth, and decreased towards the fluke, with relatively thicker blubber in the dorsal region than in the ventral and lateral regions. Significant negative correlations between BT and seasonal water temperature changes were observed in YFPs. However, different body regions display different sensitivities to seasonal temperature changes. The BT in the anal girth region exhibited noticeable seasonal changes. In contrast, the umbilical lateral and ventral regions showed relatively blunt seasonal changes, indicating different adaptive functions of the blubber in different regions. BT in the dorsal region decreased linearly with increasing water temperature. In the lateral and ventral regions, BT significantly changed with water temperature at a threshold of 18 °C. The YFPs had relatively thinner BT than similar-sized harbor porpoises that inhabit relatively high latitudes with much lower water temperatures. This further demonstrates the adaptive function of BT in response to environmental temperatures in small cetaceans. This study elucidates the seasonal pattern of BT variation in small cetaceans and provides insight into adaptation mechanisms of small cetaceans to temperature changes. [ABSTRACT FROM AUTHOR]

Understanding the distribution patterns and shaping factors of bacterial pathogens in aquatic ecosystems, especially in natural waters, are critical to the control of pathogen transmission. In this study, using 16S rRNA gene amplicon sequencing, we explored the composition and biogeographic dynamics of potential bacterial pathogens in the middle and lower reaches of the Yangtze River, as well as its two vast adjoining lakes (Dongting Lake and Poyang Lake). The pathogen community belonged to 12 potential pathogenic groups, with "intracellular parasites," "animal parasites or symbionts" and "human pathogens all" occupying 97.5% in total. The potential pathogen community covered seven phyla with Proteobacteria (69.8%) and Bacteroidetes (13.5%) the most predominant. In addition, 53 genera were identified with Legionella (15.2%) and Roseomonas (14.2%) themost dominant. The average relative abundance, alpha diversity and microbial composition of the potential bacterial pathogens exhibited significant biogeographical variations among the different sections. An in-depth analysis reflected that environmental variables significantly structured the potential bacterial pathogens, including water physiochemical properties (i.e., chlorophyll-a, total nitrogen and transparency), heavy metals (i.e., As and Ni), climate (i.e., air temperature) and land use type (i.e., waters). Compared to the overall bacterial community which was composed of both pathogenic and non-pathogenic bacteria, the pathogen community exhibited distinct microbial diversity patterns and shaping factors. This signifies the importance of different variables for shaping the pathogen community. This study represents one attempt to explore pathogen diversity patterns and their underlying drivers in the Yangtze River, which provides a foundation for the management of pathogenic bacteria. [ABSTRACT FROM AUTHOR]

An evoked-potentiai audiogram was measured for an Indo-Pacific humpback dolphin (Sousa chinensis) living in the dolphinarium of Nanning Zoo, China. Rhythmic 20 ms pip trains composed of cosine-enveloped 0.25 ms tone pips at a pip rate of 1 kHz were presented as sound stimuli. The dolphin was trained to remain still at the water surface and to wear soft latex suction-cup EEG electrodes used to measure the animal's envelope-following evoked potentials to the sound stimuli. Responses to 1000 rhythmic 20 ms pip trains for each amplitude/frequency combination were averaged and analysed using a fast Fourier transform to obtain an evoked auditory response. The hearing threshold was defined as the zero crossing point of the response input-output function using linear regression. Fourteen frequencies ranging from 5.6 to 152kHz were studied. The results showed that most of the thresholds were lower than 90dBre. 1μPa (r.m.s.), covering a frequency range from 11.2 to 128 kHz, and the lowest threshold of 47 dB was measured at 45 kHz. The audiogram, which is a function of hearing threshold versus stimulus carrier frequency, presented a U-shape with a region of high hearing sensitivity (within 20dB of the lowest threshold) between approximately 20 and 120 kHz. At frequencies lower than this high-sensitivity region, thresholds increased at a rate of approximately 11 dB octave-1 up to 93 dB at 5.6 kHz. The thresholds at high frequencies above 108 kHz increased steeply at a rate of 130 dB octave-1 up to 127dB at 152 kHz. [ABSTRACT FROM AUTHOR]

The acclimation process of Yangtze finless porpoises to a limited holding pool after their introduction to this new captive environment is presented. One male (#1) and two female (#2, #3) finless porpoises, newly captured from two different sections of China's Yangtze River, were observed in an indoor holding pool with an area of 155 m from January 1997 to January 1998 (animal #3 was removed from the pool in mid-February 1997). Three separate areas in the pool were predefined. Time spent in each of the areas was individually monitored two or three sessions a week using the focal sampling method. In total, 71.3 h of observations (316 sessions) were recorded, with an average observation time each month of about 2.4 h (10 sessions) for each porpoise. The percentage of time spent in each area per month was calculated for each porpoise, and the variations in the percentage of time spent in each area was compared. Results indicated that independent areas of activity existed among porpoises during the early stages of captivity. However, over time, the frequent approaches of the female to the male caused these areas to fade away, resulting in almost equal use of the entire pool area by the newly formed group. The existence of the independent areas of activity during the early months of captivity indicates that newly introduced individuals from different wild subgroups may need separate areas for activities. However, further studies with more animals are needed to draw more general conclusions about the individual areas of activity of this subspecies when in captivity. [ABSTRACT FROM AUTHOR]

A method is presented to estimate the density of finless porpoises using stationed passive acoustic monitoring. The number of click trains detected by stereo acoustic data loggers (A-tag) was converted to an estimate of the density of porpoises. First, an automated off-line filter was developed to detect a click train among noise, and the detection and false-alarm rates were calculated. Second, a density estimation model was proposed. The cue-production rate was measured by biologging experiments. The probability of detecting a cue and the area size were calculated from the source level, beam patterns, and a sound-propagation model. The effect of group size on the cue-detection rate was examined. Third, the proposed model was applied to estimate the density of finless porpoises at four locations from the Yangtze River to the inside of Poyang Lake. The estimated mean density of porpoises in a day decreased from the main stream to the lake. Long-term monitoring during 466 days from June 2007 to May 2009 showed variation in the density 0–4.79. However, the density was fewer than 1 porpoise/km2 during 94% of the period. These results suggest a potential gap and seasonal migration of the population in the bottleneck of Poyang Lake. [ABSTRACT FROM AUTHOR]

Data on distribution, abundance, ecology, and behavior are essential for conservation and management of endangered animals in the wild. Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) is an endangered small odontocete species, living exclusively in the Yangtze River and its connecting Poyang and Dongting Lakes. Frequent production of high-frequency bio-sonar signals allows the animal to be detectable using passive acoustic methods. Recently, a stereo acoustic event data-logger (A-tag) has been used extensively to detect the animal by using both fixed and mobile platforms. The passive acoustic monitoring methods were not only successful in detecting the presence of animals, but also in counting, localizing, and tracking phonating individuals. Underwater behavior observed acoustically helped to assess possible effects of vessels on the animals during acoustic surveys. [ABSTRACT FROM AUTHOR]

Acoustic signals from wild Neophocaena phocaenoides sunameri were recorded in the waters off Liao-dong-wan Bay located in Bohai Sea, China. Signal analysis shows that N. p. sunameri produced “typical” phocoenid clicks. The peak frequencies fp of clicks ranged from 113 to 131 kHz with an average of 121±3.78 kHz (n=71). The 3 dB bandwidths Δf ranged from 10.9 to 25.0 kHz with an average of 17.5±3.30 kHz. The signal durations Δt ranged from 56 to 109 μs with an average 80±11.49 μs. The number of cycles Nc ranged from 7 to 13 with an average of 9±1.48. With increasing peak frequency there was a faint tendency of decrease in bandwidth, which implies a nonconstant value of fp/Δf. On occasion there were some click trains with faint click energy presenting below 70 kHz, however, it was possibly introduced by interference effect from multiple pulses structures. The acoustic parameters of the clicks were compared between the investigated population and a riverine population of finless porpoise. [ABSTRACT FROM AUTHOR]

The article discusses the ex situ conservation of freshwater cetaceans Baiji and Yangtze finless porpoise in two semi-natural reserves in Shishou, Hubei Province and Tongling, Anhui Province in China to rescue them from the exploited Yangtze River system at the same time establish their viable breeding populations. Results revealed that porpoises were able to survive and reproduce in both the reserves with at least one or three calves born in each reserve each year. Releasing the animals back into the river when the natural environment has been improved should be the long term-goal and the in situ conservation efforts in natural reserves and lakes should not be abandoned. The range-wide Yangtze cetacean survey that is in preparation is expected to capture any remaining Baiji successfully.

This paper describes the high-frequency echolocation signals from free-ranging Yangtze finless porpoise in the Tian-e-zhou Baiji National Natural Reserve in Hubei Province, China. Signal analysis showed that the Yangtze finless porpoise clicks are typical high-frequency narrow-band (relative width of the frequency spectrum Q=6.6±1.56, N=548) ultrasonic pulses. The peak frequencies of the typical clicks range from 87 to 145 kHz with an average of 125±6.92 kHz. The durations range from 30 to 122 μs with an average of 68±14.12 μs. The characteristics of the signals are similar to those of other members of the Phocoenidae as well as the distantly related delphinids, Cephalorhynchus spp. Comparison of these signals to those of the baiji (Lipotes vexillifer), who occupies habitat similar to that of the Yangtze finless porpoise, showed that the peak frequencies of clicks produced by the Yangtze finless porpoise are remarkably higher than those produced by the baiji. Difference in peak frequency between the two species is probably linked to the different size of preferred prey fish. Clear double-pulse and multi-pulse reverberation structures of clicks are noticed, and there is no indication of any low-frequency (<70 kHz) components during the recording period. © 2005 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

An abstract of the study "Indirect Evidence of Boat Avoidance Behavior of Yangtze Finless Porpoises," by Songhai Li et al is presented.