UC San Diego

Sounds produced by fishes during reproductive periods are increasingly being discovered, highlighting the importance of acoustic communication within courtship and spawning behaviors across a diverse assemblage of fishes. While researchers have increased monitoring efforts of fish sounds to infer spatio-temporal patterns of spawning, habitat use, and abundance, a lack of knowledge about the relationships between recorded sounds, reproductive behaviors, and abundance has impeded progress in exposing the utility of fish sounds for understanding the reproductive biology and dynamics of regional populations.

This dissertation assesses the biological importance of sound production in Gulf grouper (Mycteroperca jordani) and Gulf corvina (Cynoscion othonopterus) and provides evidence that levels of fish sounds are indicative of reproductive activity and abundance. Long-term recordings of Gulf grouper sounds were coupled with observational data and acoustic propagation modeling to describe the mating system and acoustic behaviors of the species. Gulf grouper conformed to a protogynous life strategy and lek mating system with large males that established fixed territories, courted individual females, and pair spawned. Males produced sounds during courtship behaviors and spawning rushes that may have functioned to express fitness to prospective mates; this is the first account of sounds accompanying spawning in groupers. Rates of sound production were statistically related to measures of female abundance and reproductive activity, indicating that fish sounds can be used as estimators of relative reproductive activity and abundance of both sexes outside of observations. Mobile echosounder and passive acoustic surveys of the spawning aggregation site of Gulf corvina documented the sounds, spatial distribution, and abundance of aggregated fish. The site supported up to 1.55 million fish that contributed to a 21-fold increase in ambient noise levels through collective chorusing of the loudest fish sound yet to be documented, warranting future conservation and appreciation of acoustic communication in fishes. A predictive relationship between acoustic levels of chorusing and estimates of density was found, demonstrating that sound levels may be used to estimate the density of soniferous fishes at aggregation sites. In summary, my dissertation advances our understanding of the importance of sounds within reproductive behaviors and identifies future opportunities for improved population monitoring.