Assessing temporal patterns of nearshore fish communities through passive acoustic monitoring in a marine protected area

Abstract Passive Acoustic Monitoring (PAM) is a cost-effective, non-invasive technique with potential applications for long-term monitoring of biodiversity, species behaviour, habitat health and noise pollution at wide temporal and spatial scales. This research aimed to study temporal patterns in the acoustic fish community in a Marine Protected Area, the Professor Luiz Saldanha Marine Park (PLSMP), in Portugal. Three acoustic recorders were deployed between June 2021 and September 2022 in three sites with different rock/algae coverage within the marine park. Acoustic recordings were analysed for putative unidentified fish sounds and analysed for seasonal and diel patterns. We compared fish sounds occurrence and acoustic diversity indices (sound type Richness, Shannon, Simpson and Evenness) at the different temporal scales. Results show an increase in fish sound production and higher sound diversity indices at sunset and night, with no distinct seasonal patterns. We further explore the patterns in the occurrence of fish sounds relative to the type of habitat, and the influence of environmental factors like temperature, type of substrate or proximity to an estuary. Although spatial replicates are lacking, our results suggest that total occurrence and diversity of sounds were linked with habitat structure, as they were higher in Zone 1 (rocky habitat with kelp forest Saccorhiza polyschides ) compared to Zone 3 (interface rock/sand habitat with Treptacantha usneoides ). Other factors, such as the distance to the nearest estuary, also seemed to influence fish sound occurrence. In conclusion, our results highlight the patterns of occurrence of fish sounds in a marine protected area, highlighting the use of PAM as a supporting tool for monitoring and conservation efforts in the marine environment.