Potential impacts of shipping noise on Indo-Pacific humpback dolphins and implications for regulation and mitigation:a review

Shipping noise is a widespread and relatively loud sound source among human-induced underwater sounds.The impacts of shipping noise are of special concern for Indo-Pacific humpback dolphins(Sousa chinensis),as they inhabit shallow and nearshore habitats and are highly dependent on sound for survival.This study synthesizes our current understanding of the potential impacts of shipping noise on Indo-Pacific humpback dolphins combined with knowledge on sound production and hearing of these animals and the impacts of noise on other whales and dolphins.For further protection and management of Indo-Pacific humpback dolphins and their habitats,shipping noise should be regulated and mitigated to modify sound from ships,to reduce overall noise levels,and to set more marine protected areas(MPAs)covering most Indo-Pacific humpback dolphin habitats with seasonal and geographical restrictions to avoid ensonification of shipping noise.The emphasis for future research should be on obtaining more baseline information about the population distribution,sound production,hearing capabilities at the population level,behavior,and stress hormones of the humpback dolphins under different noise conditions or under different noise-producing activities,and/or in high-noise areas compared with relatively quiet areas,and the noise characteristics of ships of different types,sizes and speeds.

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.