Detection and localization of Goliath grouper using their low-frequency pulse sounds.

The goal of this paper is to implement and deploy an automated detector and localization model to locate underwater marine organisms using their low-frequency pulse sounds. This model is based on time difference of arrival (TDOA) and uses a two-stage approach, first, to identify the sound and, second, to localize it. In the first stage, an adaptive matched filter (MF) is designed and implemented to detect and determine the timing of the sound pulses recorded by the hydrophones. The adaptive MF measures the signal and noise levels to determine an adaptive threshold for the pulse detection. In the second stage, the detected sound pulses are fed to a TDOA localization algorithm to compute the locations of the sound source. Despite the uncertainties stemming from various factors that might cause errors in position estimates, it is shown that the errors in source locations are within the dimensions of the array. Further, our method was applied to the localization of Goliath grouper pulse-like calls from a six-hydrophone array. It was revealed that the intrinsic error of the model was about 2 m for an array spanned over 50 m. This method can be used to automatically process large amount of acoustic data and provide a precise description of small scale movements of marine organisms that produce low-frequency sound pulses.

Active acoustic surveys reveal coastal fish community resistance to an environmental perturbation in South Florida.

Coastal fish communities are under increasing levels of stress associated with climate variation and anthropogenic activities. However, the high degree of behavioral plasticity of many species within these communities allow them to cope with altered environmental conditions to some extent. Here, we combine meteorological information, data from hydroacoustic surveys, and recordings of goliath grouper sound production to examine the response of coastal fish communities to heavy rainfall events in South Florida, USA, that resulted in the release of excess storm water into surrounding estuaries and coastal waters. We observed a nearly 12,000% increase in water column acoustic backscatter following a heavy rainfall event of September 16th, 2015. Interestingly, estimates of school backscatter, a proxy for biomass, increased by 172% with the onset of the perturbation. Schooling fish density also increased by 182%, as did acoustically derived estimates of mean schooling fish length (21%). Following the perturbed period, school backscatter decreased by 406%, along with schooling density (272%), and mean schooling fish length (35%). Hydrophone and hydroacoustic data also revealed that goliath grouper (Epinephelus itajara) spawning aggregations were persistent in the region throughout the duration of the study and continued to exhibit courtship behavior during the perturbed period. Our observations demonstrate the high level of resistance common in coastal species but raises new questions regarding the threshold at which fish communities and reproductive activities are disrupted. As coastal land use continues to increase, and the effects of global climate change become more pronounced, more Before-After Control Impact (BACI) studies will provide improved insight into the overall response of nearshore communities to future perturbations and the cumulative effect of repeated perturbations over extended periods.

Localization and source level estimates of black drum (Pogonias cromis) calls.

A four hydrophone linear array was used to localize calling black drum and estimate source levels and signal propagation. A total of 1025 source level estimates averaged 165 dB(RMS) relative (re:) 1 µPa (standard deviation (SD)=1.0). The authors suggest that the diverticulated morphology of the black drum swimbladder increase the bladder's surface area, thus contributing to sound amplitude. Call energy was greatest in the fundamental frequency (94 Hz) followed by the second (188 Hz) and third harmonics (282 Hz). A square root model best described propagation of the entire call, and separately the fundamental frequency and second harmonic. A logarithmic model best described propagation of the third harmonic which was the only component to satisfy the cut-off frequency equation. Peak auditory sensitivity was 300 Hz at a 94 dB re: 1 µPa threshold based on auditory evoked potential measurements of a single black drum. Based on mean RMS source level, signal propagation, background levels, and hearing sensitivity, the communication range of black drum was estimated at 33-108 m and was limited by background levels not auditory sensitivity. This estimate assumed the source and receiver were at approximately 0.5 m above the bottom. Consecutive calls of an individual fish localized over 59 min demonstrated a mean calling period of 3.6 s (SD=0.48), mean swimming speed of 0.5 body lengths/s, and a total distance swam of 1035 m.

First report of lionfish prey from Western Florida waters as identified by DNA barcoding.

DNA barcoding was used to identify prey fragments recovered from the stomachs of lionfish harvested during the 2016 Sarasota Lionfish Derby. A total of 305 prey fragments were recovered from 50 stomachs (mean = 4.6 per stomach), of which 184 (60.3%) fragments could be identified to either species or genus when Cytochrome Oxidase I (COI) sequences were queried against the Barcode of Life Database. We identified 21 fish prey species which represented fourteen families and accounted for 95.7% of genetically identifiable prey items. The remaining prey items identified corresponded to six crustacean species. The four most common prey taxa in lionfish stomachs were Ptereleotris calliura (24.3%), an unidentified Microgobius species (20.4%), Diplectum formosum (14.3%), and Apogon aurolineatus (12.2%). The most frequently observed crustacean species, Metapenaeopsis goodei, was found in only three stomachs (6.1%). We also report eleven taxa as putative novel lionfish prey species, most of which are common in Florida waters. Sixteen prey items were identified as lionfish (P. volitans); however, it was not definitive whether these detections were due to cross contamination or cannibalization. This represents the first report of lionfish diets from Florida waters in the Eastern Gulf of Mexico based on barcoding efforts. Our results are largely congruent with previous COI barcoding based studies of lionfish diets, indicating these predators to be generalists exhibiting preferences for specific prey traits but with regional differences in their diets.

Effects of Hurricane Charley on fish chorusing.

Hurricane Charley, a category 4 hurricane, passed through Charlotte Harbor, Florida, directly over an autonomous underwater acoustic datalogger used to record sound production by fishes associated with courtship and spawning. Acoustic recordings made on 9 days prior to the storm, during and 3 days after the storm provided unprecedented documentation of the hurricane's passage and its effect on fishes' calling behaviour. The hurricane did not inhibit nightly chorusing events of spawning fish. Sound levels produced by spawning fish on the night of and 3 days after the hurricane were higher and lasted longer than any of the 9 days recorded prior to the hurricane.