Estimating fish abundance at spawning aggregations from courtship sound levels

Abstract

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.

Potential for grouper acoustic competition and partitioning at a multispecies spawning site off Little Cayman, Cayman Islands

“…Since these epinephelids are known to produce courtship-associated sound (CAS), knowledge of how they share their acoustic space may lead to a better understanding of their reproductive ecology. Furthermore, it may aid in continued monitoring and management of these species as well as the discovery of other spawning aggregations (Rowell et al 2012(Rowell et al , 2017.…”

Recovery of critically endangered Nassau grouper ( Epinephelus striatus ) in the Cayman Islands following targeted conservation actions

“…The logistical challenges associated with collecting the types of data we present here over a decade or more of sampling will likely preclude the replication of our approach and findings at many, if not most, FSAs. On the other hand, emerging technologies, such as passive and active acoustics (75)(76)(77)(78), hold promise for providing alternative forms of fisheries-independent observations to document conservation success elsewhere. While we observed increases in FSA size on both Little Cayman and Cayman Brac, in neither case was the growth immediate or constant through time.…”

Freshwater ecoacoustics as a tool for continuous ecosystem monitoring

“… for an overview) and were recently used to estimate fish abundance in a marine fish species, the Gulf corvina ( Cynoscion othonopterus ) (Rowell et al . ); and Movement: acoustic monitoring has been used in marine systems to characterize spatiotemporal variation in Atlantic cod ( Gadus morhua ) via sounds associated with spawning (Hernandez et al . ).…”

“…• Species presence or absence: for instance, acoustic monitoring has been used in freshwater systems to detect invasive tilapia (Kottege et al 2015 Amorim et al [2015] for an overview) and were recently used to estimate fish abundance in a marine fish species, the Gulf corvina (Cynoscion othonopterus) (Rowell et al 2017); and • Movement: acoustic monitoring has been used in marine systems to characterize spatiotemporal variation in Atlantic cod (Gadus morhua) via sounds associated with spawning (Hernandez et al 2013).…”