Identification of Antarctic minke and killer whales with passive acoustic monitoring in Prydz Bay, Antarctica

Although four species of odontocete and four species of baleen whale have been recorded in Prydz Bay,their vocalizations have been rarely investigated.Underwater vocalizations were recorded during March 2017 in Prydz Bay,Antarctica.Bio-duck sounds,downsweeps,inverted“u”shape signals,whistles,pulsed sounds,and broadband clicks were recorded.Bio-duck sounds and downsweeps were associated with Antarctic minke whales(Balaenoptera bonaerensis)based on visual observations.Similarities between inverted“u”shape signals,biphonic calls,and clicks with vocalizations previously described for killer whales(Orcinus orca)lead us believe the presence of Antarctic killer whales.According to sound structures,signal characteristics,and recording location,Antarctic type C killer whales were the most probable candidates to produce these detected calls.These represent the fi rst detection of inverted“u”shape signals in Antarctic waters,and the fi rst report of Antarctic killer whale in Prydz Bay based on passive acoustic monitoring.The co-existence of Antarctic minke and killer whales may imply that minke whales can detect diff erences between the sounds of mammal-eating and fi sh-eating killer whales.Our descriptions of these underwater vocalizations contribute to the limited body of information regarding the distribution and acoustic behavior of cetaceans in Prydz Bay.

Association between porpoise presence and fish choruses:implications for feeding strategies and ecosystem-based conservation of the East Asian finless porpoise

The associations between feeding activities and environmental variables inform animal feeding tactics that max-imize energetic gains by minimizing energy costs while maximizing feeding success.Relevant studies in aquatic animals,particularly marine mammals,are scarce due to difficulties in the observation of feeding behaviors in aquatic environments.This data scarcity concurrently hinders ecosystem-basedfishery management in the context of small toothed-cetacean conservation.In the present study,a passive acoustic monitoring station was deployed in an East Asianfinless porpoise habitat in Laizhou Bay to investigate potential relationships between East Asianfinless porpoises and their prey.The data revealed that porpoises were acoustically present nearly every day during the survey period.Porpoise detection rates differed between spring and autumn in concert with activities offish choruses.During spring,fish choruses were present throughout the afternoon,and this was the time when porpoise vocalizations were the most frequently detected.During autumn,whenfish choruses were absent,porpoise detec-tion rates decreased,and diurnal patterns were not detected.The close association betweenfish choruses andfin-less porpoise activities implies an“eavesdropping”feeding strategy to maximize energetic gains,similar to other toothed cetaceans that are known to engage similar feeding strategies.Underwater noise pollution,particularly those maskingfish choruses,could interruptfinless porpoises’feeding success.Fisheries competing soniferousfishes withfinless porpoise could impactfinless porpoise viability through ecosystem disruption,in addition tofishing gear entanglement.

Frequent and prolonged nocturnal occupation of port areas by Yangtze finless porpoises (Neophocaena asiaeorientalis): Forced choice for feeding?

During the Yangtze Freshwater Dolphin Expedition 2012,Yangtze finless porpoises(Neophocaena asiaeorientalis)were acoustically monitored in 9 port areas at night.During 6566 min of nocturnal monitoring,porpoise sonar was detected for 488 min(7.43%of the total time).Of all 81 encounters,the longest echolocation span obtained was 102.9 min,suggesting frequent and prolonged porpoise occupation of the port areas.A combined total of 2091 click trains were recorded,with 129(6.2%)containing minimum inter-click intervals(ICIs)below 10 ms(termed a buzz).Buzzes with a decrease in ICIs and search and approach phases that resembled feeding echolocation signals accounted for 44.2%(N=52)of all buzzes.Buzzes with an increase in ICIs,suggesting a mirrored prey capture phase,accounted for 20.2%(N=26)and could reflect attempts to locate escaped prey because they were followed by approach-phase feeding buzzes.Anecdotal evidence of porpoises fleeing the proximity of vessels was observed.The recordings indicating clusters of porpoises feeding near the port areas suggest a forced choice for feeding due to the relatively higher prey availability in the port areas compared to other areas in the Yangtze River that are probably overfished.

Population size estimation of chirp and grunt generating fish and mammals using cross-correlation based technique with three acoustic sensors

Passive acoustic monitoring has the potential to be a useful tool for population estimation of sound-producing fish and mammals(mostly whales).Previous work on population estimates of callers employed a simple cross-correlation technique with recordings from two acoustic sensors,and the current work extends the technique to two configurations of a 3-acoustic sensors array using two different sounds,i.e.,chirps which is commonly generated by damselfish(Dascyllus aruanus),humpback whales(Megaptera novaeangliae),dugongs(Dugong dugon)etc.,species,and grunts which is commonly generated by Japanese gurnard(Chelidonichthys kumu),Grey gurnard(Eutrigla gurnardus),gulf toadfish(O.beta),etc.,species.We compared simulated results from this technique with values determined by theoretical approach.We have found that an increasing number of cross-correlation function(CCF)provide better results using this technique.However,the technique has some limitations including negligence of multipath interference,assuming the delays to be integer.