Regional abundances of Nassau grouper Epinephelus striatus and yellowfin grouperMycteroperca venenosa have declined due to overfishing of their spawning aggregations, prompting permanent and seasonal fisheries closures in the US Virgin Islands (USVI). As both species produce sounds associated with reproductive behaviors (courtship-associated sounds; CAS), passive acoustic and acoustic telemetry methods were used to determine temporal patterns of reproductive activity, site usage, and fish movements in order to assess the effectiveness of current management strategies at 2 marine protected areas (MPAs) in the USVI: the Grammanik Bank (GB) and Hind Bank Marine Conservation District (MCD). Patterns of sound production and ultrasonic acoustic tag detections showed that both species formed spawning aggregations from January through May at the GB, highlighting the current seasonal regulations (1 February to 30 April) as insufficient for protecting spawning stocks during the entire reproductive season. Acoustic tagging confirmed connectivity between the GB and MCD and exposed the broad extent of habitat used, including non-protected areas, during the spawning season. Spawning did not likely occur within the MCD, but the MPA did support abundances of calling individuals during spawning periods, indicating that both species produce CAS away from their spawning sites. This finding coupled with the detection of routine migrations between spawning and non-spawning sites presents a potential mechanism to lead conspecifics to the aggregation site and thereby increase reproductive fitness and spawning output. KEY WORDS: Nassau grouper • Epinephelus striatus • Yellowfin grouper • Mycteroperca venenosa • Passive acoustics • Ultrasonic acoustic tagging • Fish movement patterns • Marine protected area Resale or republication not permitted without written consent of the publisher
Sound produced by fish spawning aggregations (FSAs) permits the use of passive acoustic methods to identify the timing and location of spawning. However, difficulties in relating sound levels to abundance have impeded the use of passive acoustics to conduct quantitative assessments of biomass. Here we show that models of measured fish sound production versus independently measured fish density can be generated to estimate abundance and biomass from sound levels at FSAs. We compared sound levels produced by spawning Gulf Corvina (Cynoscion othonopterus) with simultaneous measurements of density from active acoustic surveys in the Colorado River Delta, Mexico. During the formation of FSAs, we estimated peak abundance at 1.53 to 1.55 million fish, which equated to a biomass of 2,133 to 2,145 metric tons. Sound levels ranged from 0.02 to 12,738 Pa2, with larger measurements observed on outgoing tides. The relationship between sound levels and densities was variable across the duration of surveys but stabilized during the peak spawning period after high tide to produce a linear relationship. Our results support the use of active acoustic methods to estimate density, abundance, and biomass of fish at FSAs; using appropriately scaled empirical relationships, sound levels can be used to infer these estimates.
Annual spawning aggregations of red hind Epinephelus guttatus form at predictable times and locations and have historically succumbed to overfishing. Monitoring the status and restoration of aggregations is essential for evaluating the effectiveness of fishery management measures. Passive acoustic and diver-based underwater visual census (UVC) techniques were used to develop an efficient method for estimating red hind density from sound production at spawning aggregations. Red hind sound production was recorded from November 2010 to April 2011 at Abrir la Sierra, Puerto Rico. UVC surveys were conducted during the spawning season to assess changes in red hind density over a fixed time and area. Sound recorded from 18:00 to 19:00 h Atlantic Standard Time (UTC − 4) was representative of total daily changes in red hind sound production and was selected for the development of an efficient density estimation model. Pronounced daily changes in sound production and density were observed after the December 2010 and January 2011 full moons. Two hourly sound level measurements were compared to densities estimated by UVC surveys, yielding significant linear regressions, which were used to predict changes in fish density as measured at the aggregation site. Passive acoustic methods allowed to predict changes in red hind density and habitat use at a higher temporal resolution than previously possible with traditional methods. Red hind sound production and inferred densities can be monitored and analyzed efficiently for multiple aggregation sites simultaneously, documenting short-term and long-term changes in red hind densities at spawning aggregation sites and providing important information for the support or development of management strategies.
Group choruses of marine animals can produce extraordinarily loud sounds that markedly elevate levels of the ambient soundscape. We investigated sound production in the Gulf corvina (), a soniferous marine fish with a unique reproductive behaviour threatened by overfishing, to compare with sounds produced by other marine animals. We coupled echosounder and hydrophone surveys to estimate the magnitude of the aggregation and sounds produced during spawning. We characterized individual calls and documented changes in the soundscape generated by the presence of as many as 1.5 million corvina within a spawning aggregation spanning distances up to 27 km. We show that calls by male corvina represent the loudest sounds recorded in a marine fish, and the spatio-temporal magnitude of their collective choruses are among the loudest animal sounds recorded in aquatic environments. While this wildlife spectacle is at great risk of disappearing due to overfishing, regional conservation efforts are focused on other endangered marine animals.
Soundscapes offer rich descriptions of composite acoustic environments. Characterizing marine soundscapes simply through sound levels results in incomplete descriptions, limits the understanding of unique features, and impedes meaningful comparisons. Sources that contribute to sound level metrics shift in time and space with changes in biological patterns, physical forces, and human activity. The presence of a constant or chronic source is often interwoven with episodic sounds. Further, the presence and intensity of sources can influence other sources, calling for a more integrated approach to characterizing soundscapes. Here, we illustrate this complexity using data from a national-scale effort, the Sanctuary Soundscape Monitoring Project (SanctSound), an initiative designed to support collection of biological, environmental, and human use data to compliment the interpretation of sound level measurements. Using nine examples from this diverse dataset we demonstrate the benefit of integrating source identification and site features to interpret sound levels across a diversity of shallow water marine soundscapes (<150 m). Sound levels from sites in high human use areas reflect the anthropogenic influences on the soundscape, especially when measuring broad frequency bands, whereas sites with relatively low human activity and high sound levels reveal biological features of the soundscape. At sites with large tidal changes, sound levels correlated with the magnitude of tidal flow, and sound levels during high tidal flow periods were similar to sound levels at sites near commercial shipping lanes. At sites in relatively close proximity (<30 km), sound levels diverge because of the presence of different proximate sound contributors and propagation features of the site. A review of emerging methodologies for integrated soundscape analysis, including acoustic scenes, provides a framework for interpreting soundscapes across a variety of conditions. With a global growth in monitoring efforts collecting standardized measurements over widely distributed arrays, more integrated methods are needed to advance the utility of soundscapes in marine resource management.
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