Last call: Passive acoustic monitoring shows continued rapid decline of critically endangered vaquita.

The vaquita is a critically endangered species of porpoise. It produces echolocation clicks, making it a good candidate for passive acoustic monitoring. A systematic grid of sensors has been deployed for 3 months annually since 2011; results from 2016 are reported here. Statistical models (to compensate for non-uniform data loss) show an overall decline in the acoustic detection rate between 2015 and 2016 of 49% (95% credible interval 82% decline to 8% increase), and total decline between 2011 and 2016 of over 90%. Assuming the acoustic detection rate is proportional to population size, approximately 30 vaquita (95% credible interval 8-96) remained in November 2016.

Social responses of travelling finless porpoises to boat traffic risk in Misumi West Port, Ariake Sound, Japan.

Anthropogenic effects have created various risks for wild animals. Boat traffic is one of the most fatal risks for marine mammals. Individual behavioral responses of cetaceans, including diving behavior such as changing swimming direction and lengthing inter-breath interval, to passing boats is relatively well known; however, the social function of cetacean responses to boat traffic in a natural setting remains poorly understood. We focused on describing the behavioral responses of single and aggregated finless porpoises to boats passing at Misumi West Port, Ariake Sound, Japan, by using a drone characterized with a high-precision bird's-eye angle. During the study period, we collected 25 episodes of finless porpoise responses to boats passing by. A mean (± SEM) of 5.1 ± 1.0 individuals were observed for each episode. The primary response to passing boats was avoidance by dive, which implies boat traffic is a substantial disturbance to finless porpoises that travel along the seawater surface daily. The diving duration decreased significantly with an increase in the number of aggregated individuals. The diving and floating reaction times were 10.9 ± 2.3 s and 18.7 ± 5.0 s, respectively. There was no significant difference between the reaction times indicating that each individual was motivated to keep the group cohesion consistent when floating even after the risk had dissolved, which is comparable to the behavior of porpoises that dive when riskier conditions are present, such as when a boat approaches an aggregation. Our findings provide new insights on the sociality of finless porpoises even though there were limitations, like an inability to identify a specific individual. The drone enabled us to observe the social behavior of finless porpoises and other cetaceans at an unprecedented resolution, which may lead to a better understanding of the evolutionary diversity of intelligence and sociality and the bridge to human evolution.

Trends in the maternal investment of harbour porpoises are uncoupled from the dynamics of their primary prey.

Harbour porpoises in the Bay of Fundy and Gulf of Maine feed primarily on Atlantic herring. Herring stocks have undergone dramatic fluctuations in abundance over the past three decades due to changes in fishing intensity. In order to understand the effects of these changes in prey abundance on the patterns of maternal investment, I examined interdecadal variation in the size of porpoise calves measured in August prior to weaning. Female harbour porpoises exhibited significant variation in maternal investment between 1970 and 1999. During the 1980s, females consumed more herring and produced larger calves. Surprisingly, however, this increased maternal investment occurred during the period of lowest prey abundance, perhaps because the herring stock assessment does not reflect the availability or quality of prey to female porpoises.

The influence of three acoustic alarms on the behaviour of harbour porpoises (Phocoena phocoena) in a floating pen.

Harbour porpoise bycatch may be reduced by deterring porpoises from nets acoustically. In this study, two harbour porpoises were subjected to three acoustic alarms. The effect of each alarm was judged by comparing the animals' position and respiration rate during a test period with that during a baseline period. The XP-10 alarm produced 0.3 s tonal signals randomly selected from a set of 16 with fundamental frequencies between 9 and 15 kHz, with a constant pulse interval of 4.8 s (duty cycle 6%). The 2MP alarm produced 0.3 s tonal signals randomly selected from a set of 16 with similar fundamental frequencies but with random pulse intervals of between 2 and 5 s (duty cycle 8%). The frequency spectra and source levels of the 2MP and XP-10 alarms varied depending on the signal selected. The HS20-80 alarm produced a constant, but asymmetrical frequency modulated sinewave between 20 and 80 kHz with total pulse duration of 0.3 s. with random pulse intervals of between 2 and 5 s (duty cycle 4.6%). The porpoises reacted to all three alarms by swimming away from them and by increasing their respiration rate. The XP-10, which on average had the highest source level, had the strongest effect.

Ethogram of Yangtze finless porpoise calves (Neophocaena phocaenoides asiaeorientalis).

Underwater behavioral patterns of one Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) calf in captivity and those performed on the water surface by two calves in semi-natural environment were focally followed and continuously recorded until one year postpartum to construct the ethogram. The results indicate that 1) the three calves could display diverse and active behavioral patterns; 2) soon after birth, patterns critical for survival appeared first; 3) playful and social patterns predominated the ethogram; 4) most of the patterns were alike across age classes; 5) most of the patterns appeared at the calves' early life stage. It is possible that the above characteristics are adaptively shaped by the aquatic and social life of this subspecies.

On the performance of automated porpoise-click-detectors in experiments with captive harbor porpoises (Phocoena phocoena).

Recently, automated porpoise-click-detectors (T-PODs, Chelonia-Marine-Research) have been used intensively in monitoring harbor porpoises (Phocoena phocoena) in the wild. However, the automated click-detection-mechanism of the T-POD leads to questions on the characteristics of the detection process. We undertook experiments with six captive harbor porpoises (four subadult males in one pool, two adult males in another) at the Dolfinarium Harderwijk (Netherlands). One T-POD was placed for over a week in each pool, while the behavior of the porpoises was logged by visual observation. Data were analyzed using the T-POD software. A total of 725 431 clicks in 30 090 trains were recorded with 32% of the trains classified as CET HI, 27% as CET LO, and 41% as DOUBTFUL. All three train classes differed significantly in all parameters, except for click duration. We conclude that T-PODs perform generally well in detecting click trains of harbor porpoises but that in any future study trains classified as being of lower probability should be investigated very carefully to avoid the risk of losing valuable information.

Echolocation range of captive and free-ranging baiji (Lipotes vexillifer), finless porpoise (Neophocaena phocaenoides), and bottlenose dolphin (Tursiops truncatus).

The interclick intervals of captive dolphins are known to be longer than the two-way transit time between the dolphin and a target. In the present study, the interclick intervals of free-ranging baiji, finless porpoises, and bottlenose dolphins in the wild and in captivity were compared. The click intervals in open waters ranged up to 100-200 ms, whereas the click intervals in captivity were in the order of 4-28 ms. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging, sometimes up to 140 m. Additionally, the difference of waveform characteristics of clicks between species was recognized in the frequency of maximum energy and the click duration.