Fish chorusing patterns in California (USA) National Marine Sanctuaries

Marine soundscapes can be dominated by fish chorusing when many fish call concurrently, often for mating purposes. Passive acoustic data analysis allows us to determine spatiotemporal patterns of fish chorusing, providing insights into breeding areas, mating times, and species distributions. Our first goal was to determine which species, where, and when fishes chorused in California (USA) National Marine Sanctuaries (NMS), and our second was to assess whether fishes engaged in acoustic niche partitioning or clustering. Through the Sanctuary Soundscape Monitoring project, we collected passive acoustic data across 9 sites in Monterey Bay, Chumash Heritage, and Channel Islands NMS, each recording for approximately 2 years, totaling 18.3 recording-years. We identified (1) who: 5 distinct fish choruses including bocaccio rockfish, plainfin midshipman toadfish, white seabass, and 2 unidentified fishes; (2) where: spatial patterns varied across sites, including differences in chorus types, total number of choruses, and proportion of time with chorusing; (3) when: temporal patterns, showing primarily nocturnal and seasonal chorusing, largely aligned with reproductive cycles; (4) how: patterns of niche partitioning vs. clustering. Chorusing was clustered in time during prime chorusing season nights but was largely partitioned in peak frequency. However, for midshipman and bocaccio, which had similar peak frequencies, midshipman harmonic bandwidth increased as more choruses co-occurred, potentially due to masking. This frequency modulation may also reflect seasonal changes related to calling fatigue or temperature fluctuations. Passive acoustic monitoring of fish chorusing offers a powerful, noninvasive tool for understanding reproductive behavior, offering key ecological insights to guide effective management.