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Passive acoustic monitoring of epinephelids in Little Cayman, Cayman Islands


Marine fish are a valuable nutritional and economic resource for many communities world- wide. However, many populations have declined due to excessive exploitation and limited regulations. More than 800 species of fish produce sound which enables the use passive acoustic methods to monitor these species. Epinephelids, commonly known as groupers, are a family of fishes that account for a significant percentage of the commercial and artisanal fisheries worldwide but have experienced population declines due to high fishing pressure. Their life-history features, such as long life and formation of spawning aggregations, make them vulnerable to fishing pressure. A number of species within this family produce sound including Nassau grouper (Epinephelus striatus), red hind (E. guttatus), black grouper (Mycteroperca bonaci), and yellowfin grouper (M. venonosa). These four species are common throughout the Caribbean and targeted by fishing. I used passive acoustic data collected in Little Cayman, Cayman Islands from 2013 to 2017 to study the calling and spawning behavior and acoustic communication of these fishes. I applied signal processing and machine learning techniques and passive acoustic localization to reveal information about the calls of these species and their presence at a known Nassau grouper spawning site. I found that Nassau grouper, red hind, and black grouper calls were present all or the majority of the year with peak calling during the spawning season at this location. However, yellowfin grouper calls were scarce. Calling was correlated with lunar phase and, for most species, significantly different between tidal stages. These fishes likely use a combination of time, space, and frequency to partition their acoustic space. Localization enabled observations of small-scale movements during the spawning aggregations of Nassau grouper and red hind at night, a period previously unobserved, and showed that calling ceased for Nassau grouper after sunset and for red hind near sunrise. The first direct source level measurements for these species ranged from 144 to 155 dB re : 1μPa at 1 m. The methods and results that I present can be used to further study, monitor, and manage these species and other sound-producing fishes and may lead to improved or adaptive management strategies.

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