Temporal dynamics in diversity patterns of fish sound production in the Condor seamount (Azores, NE Atlantic)

English. peer reviewed

English. Fish sounds are important components of Azorean soundscapes. Therefore, unraveling their patterns can contribute to a better assessment of local biodiversity dynamics. Passive Acoustic Monitoring (PAM) is a cost-effective, non-intrusive method providing long-term information regardless of weather or logistic conditions, which can be especially useful when monitoring remote areas. Using PAM, we assess temporal dynamics of fish vocal activity in a protected seamount and validate PAM as an important tool for biodiversity assessment in deep-sea fish communities. Thus, we evaluated the annual, seasonal and diel patterns of variation of putative fish sounds identified in an Azorean protected seamount, the Condor (ca.190 m depth). Here, 3 years (2008, 2010 and 2012) of acoustic data were collected and analysed for diversity and abundance of the most prevalent fish sounds. We compared abundance and diversity of fish sounds before and after the establishment of the marine protected area in 2010, to assess its initial protection effects. We also compared abundance and biodiversity measures (richness and Shannon diversity index) of acoustic data with fishing data from deep-water longline surveys, to verify if acoustic diversity and taxonomic diversity show a similar trend. Additionally, we estimated a likely distance range of fish sound sources from the acoustic data loggers for local background noise and typical fish sound levels. Estimated detection distance of different fish sounds, considering Condor background noise level and reported fish sound source levels, were typically larger than 10 m and could reach hundreds of meters in some species suggesting that this study potentially targeted sounds of the deep-sea fish fauna. Fish acoustic activity was prevalent at dusks and nights of all years, while no overall seasonal pattern was detected. However, one sound sequence (#1) was dominant in the autumns of all studied period. A decrease in abundance and richness of sounds was observed from 2008 to 2012 in line with the results of fishing surveys. Although unexpected, these consistent trends suggest that PAM provides a reliable representation of fish biodiversity dynamics. Taken together, this study shows that monitoring fish sounds with PAM is a valid and promising tool for fish biodiversity assessment in deep Azorean seamounts. © 2020 Elsevier Ltd

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