| Bahaba taipingensis,which belong to Osteichthyes Perciformes Sciaenidae Bahaba,is a large warm demersal fish lived in nearshore deep water.B.taipingensis usually perches in water with a depth of 20～30 m.B.taipingensis is endemic to China and distributed in the northern South China Sea and southern East China Sea,particularly in the Pearl River Estuary.It was listed as the Grade Ⅱ State Protected Species in the Peoples Republic of China in 1988 and critically endangered in the IUCN Red List of Threatened Species in 2006.The Pearl River Estuary is the main habitat of B.taipingensis.The activities of spawning and feeding were carried out in this area.From the 1960 s and 1970 s,B.taipingensis is an important fishing product in the Pearl River Estuary,with an annual production of 180 tons.In the early 1980 s,B.taipingensis still accounted for 9.0% of the local fishing production.However,the stock of B.taipingensis sharply declined in the past 40 years,due to the overfishing,environmental degradation and habitat fragmentation in the Pearl River Estuary caused by the rapid development of society,the growth of population,as well as the construction such as the harbors and channels.The research on the protective biology of B.taipingensis is very limited.Its life history,key habitats(e.g.spawning grounds,feeding grounds and antenatal habitat),migratory and reproductive biology are still unknown.Traditional biological investigation methods are difficult to obtain samples and may also cause damage or even death to the protective species of B.taipingensis.While B.taipingensis can make sound through its swim bladder.The inflatable swim bladder like a small drum and the drum muscle in swim bladder wall is similar to drum hammer.The swim bladder flex rhythmicly and vibrate to make drum sound.The drum sound can be heard even a hundred meters away.The vocal behavior of fish is closely related to the breeding,defense,feeding and other behaviors.Therefore,the study of acoustic spectrum and underwater noise environment can be carried using the acoustic characteristics of B.taipingensis,and through underwater noise investigation in its habitats.It has important scientific value for develop the non destructive investigation method of B.taipingensis based on voiceprint recognition,and study of the vocal behavior effected by the underwater noise pollution.The acoustic monitoring on B.taipingensis was carried out in the Dongguan Bahaba taipingensis nature reserve from March to May in 2017.Ninety-six individuals lived in an indoor aquarrium and two outdoor ponds were examined.Acoustic monitor in the mentioned 3 areas carried out for two periods of time and every period of time last 7 days and nights.The results showed that 246 sounds were monitored in total,which belonged to7 types,such as drum sound,humming sound,cracking sound,clacking sound,birds sound,chagoo sound and other sounds.No significant difference was observed in the number of day and night sounds.The drum sounds was the main sound of Bahaba taipingensis sound,which account175 times.The drums were composed of 1 to 3 pulses and are dominated by a single pulse type of drum,139 times.The drums had some sine shaped waveform.The drum sound’s energy was mainly ranged from 0 to 1 000 Hz and its voiceprint was parallel to the timeline.The drum sound’s spectral frequency peaks was ranged from 50 to 140 Hz.The energy distribution and spectral frequency peak of the clacking sound was similar to the drum sound’s,whose energy is mainly from 0 to 1 000 Hz and its spectral frequency peak was from 180 to 190 Hz.The energy distribution and frequency of the humming sound,cracking sound,birds sound,chagoo sound was both at low frequencies(0～1 000 Hz)and high frequencies(3000～10 000 Hz).Pulse length,width and interval of the drum sound respectively were 67 to 1 333 ms,35 to 733 ms and 0 to 1 130 ms,whose mean value were respectively 279 ms,70 ms and 183 ms.The length of the drum and the pulse interval increases with the increase of the pulse number of sound signals,while the pulse width was shortened.Two cruises for ecological underwater noise environment investigation in two habitats of B.taipingensis also the areas of Guishan and Jinwan offshore wind farms located in Pearl River estuary were carried out in November 23,2017 and March 2,2018.In the Guishan offshore wind farm,the full noise band cumulative sound pressure level of 5monitoring stations was 70～87 d B,the noise band sound pressure level was21～72 d B,the noise pressure spectrum level was 7～33 d B,the frequency band below 100 Hz was 21～38 d B,and the noise pressure spectrum level was 7～21 d B.In the Jinwan offshore wind farm,the full noise band cumulative sound pressure level of 9 monitoring stations was 69～86 d B,the noise band sound pressure level was 19～71 d B,the noise pressure spectrum level was 3～30 d B,the frequency band below 100 Hz was 19～45d B,and the noise pressure spectrum level was 3～30 d B.The noise pressure spectrum level of underwater environment background noise of two wind farms falled below 100 Hz,and then decreases with the increase of frequency,then tended to be stable,and increases with the increase of frequency at more than 5 000 Hz.The underwater noise can reach 95 d B at 1 000 m from the pile foundation during the pile foundation construction of the offshore wind power,its slightly overlaped with the range of hearing threshold(93～99d B)of juvenile fish of the Sciaenidae.The safety distance to the underwater noise was at least 1 500～2 500 m from pile foundation.I speculated that the underwater noise had adverse effects on the habitat and migration of B.taipingensis during the construction of the pile foundation in the offshore wind power farms in the Pearl River Estuary.The variation of underwater noise environment in the offshore wind power operation was closely related to the single machine power and sea condition.The main frequency of underwater noise ranged from 60 to 359 Hz during fan operation,it covered the peak frequency of B.taipingensis which were below 200 Hz,and may interfere with the transmission of sound signal between indivuduals.In addition,when the sea condition was poor,the underwater noise intensity would increase,which was more likely to exceed the auditory threshold of the croaker fish and the effect on the hearing threshold of B.taipingensis would also be enhanced. |
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