Estimating Florida manatee (Trichechus manatus latirostris) abundance using passive acoustic methods

T.A.M.’s contribution was conducted under the ACCURATE project, funded by the U.S. Navy Living Marine Resources program (Contract No. N3943019C2176) with partial support by CEAUL (funded by FCT— Fundação para a Ciência e a Tecnologia, Portugal, through the project UIDB/00006/2020).Manatees are difficult to detect, particularly cryptic populations that inhabit areas with limited water clarity. The effectiveness of using vocal detections to estimate manatee abundance was evaluated in a clear water spring where manatees congregate seasonally. Vocalizations were extracted by a detection classifier that clustered sounds with similar spectral properties. Vocalization counts from recordings in Blue Spring, FL, USA were strong predictors of manatee abundance. The link between independent visual counts and abundance estimates from passive acoustic monitoring was used to provide an estimate of 1.059 (95% confidence interval 0.963–1.127) vocalizations/manatee/5-min, which might be used elsewhere for cue counting of manatees.Publisher PDFPeer reviewe

Acoustic methods improve the detection of the endangered African manatee

The African manatee (Trichechus senegalensis) is an elusive, data-deficient, and endangered species which inhabits marine and freshwater systems throughout Western and Central Africa. A major challenge in understanding the species ecology and distribution is the difficulty in detecting it using traditional visual surveys. The recent invasion of Giant Salvinia (Salvinia molesta) at the most important site for the species in Cameroon further limits their detectability and may restrict their movements and habitat use. To investigate methods’ effectiveness in detecting African manatees, we conducted monthly vessel surveys from which visual point scans, 360° sonar scans, and passive acoustic monitoring were conducted simultaneously at ten locations and over 12 months in Lake Ossa, Cameroon. Manatee detection frequency was calculated for each method and the influence of some environmental conditions on the methods’ effectiveness and manatee detection likelihood was assessed by fitting a binary logistic regression to our data. Detection frequencies were significantly different between methods (p < 0.01) with passive acoustics being the most successful (24.17%; n = 120), followed by the 360° sonar scan (11.67%; n = 120), and the visual point scan (3.33%; n = 120). The likelihood of detecting manatees in Lake Ossa was significantly influenced by water depth (p = 0.02) and transparency (p < 0.01). It was more likely to detect manatees in shallower water depths and higher water transparency. Passive acoustic detections were more effective in uninvaded areas of the Lake. We recommend using passive acoustics to enhance African manatee detections in future surveys

Comparison of the marine soundscape before and during the COVID-19 pandemic in dolphin habitat in Sarasota Bay, FL

Funding: Mote Scientific Foundation provided funding for the initial development of PALS. P.L.T. acknowledges support by the Office of Naval Research (Grant Nos. N000142012697 and N000142112096) and the Strategic Environmental Research and Development Program (Grant Nos. RC20-1097, RC20-7188, and RC21-3091).During the COVID-19 pandemic, decreases in large vessel activity and low-frequency noise have been reported globally. Sarasota Bay is home to a large and increasing number of recreational vessels, as well as a long-term resident community of bottlenose dolphins, Tursiops truncatus. We analyzed data from two hydrophones to compare the soundscape during the COVID-19 pandemic to previous years (March–May 2020 and 2018/2019). Hourly metrics were calculated: vessel passes, 95th percentile noise levels (125 and 16 kHz Third Octave Bands (TOBs) and two broadbands: 88–1122 Hz, 1781–17959 Hz), and dolphin whistle detection, to understand changes in vessel activity and the effect on wildlife. Vessel activity increased during COVID-19 restrictions by almost 80% at one site and remained the same at the other. Changes in noise levels varied between sites. Only the 125 Hz TOB and 88–1122 Hz band increased with vessel activity at both sites, suggesting this may be an appropriate measure of noise from small vessels in very shallow (<10 m) habitats. Dolphin whistle detection decreased during COVID-19 restrictions at one site but remained the same at the site that experienced increased vessel activity. Our results suggest that pandemic effects on wildlife should not be considered to be homogeneous globally.Publisher PDFPeer reviewe

Data from: A quantitative framework for investigating risk of deadly collisions between marine wildlife and boats

Speed regulations of watercraft in protected areas are designed to reduce lethal collisions with wildlife but can have economic consequences. We present a quantitative framework for investigating the risk of deadly collisions between boats and wildlife. We apply encounter rate theory to demonstrate how marine mammal-boat encounter rate can be used to predict the expected number of deaths associated with management scenarios. We illustrate our approach with management scenarios for two endangered species: the Florida manatee Trichechus manatus latirostris and the North Atlantic right whale Eubalaena glacialis. We used a Monte Carlo simulation approach to demonstrate the uncertainty that is associated with our estimate of relative mortality. We show that encounter rate increased with vessel speed but that the expected number of encounters varies depending on the boating activities considered. For instance, in a scenario involving manatees and boating activities such as water skiing, the expected number of encounters in a given area (in a fixed time interval) increased with vessel speed. In another scenario in which a vessel made a transit of fixed length the expected number of encounters decreases slightly with boat speed. In both cases the expected number of encounters increased with distanced travelled by the boat. For whales, we found a slight reduction (~0.1%) in the number of encounters under a scenario where speed is unregulated; this reduction, however, is negligible, and overall expected relative mortality was ~30% lower under the scenario with speed regulation. The probability of avoidance by the animal or vessel was set to 0 because of lack of data, but we explored the importance of this parameter on the model predictions. In fact, expected relative mortality under speed regulations decreases even further when the probability of avoidance is a decreasing function of vessel speed. By applying encounter rate theory to the case of boat collisions with marine mammals, we gained new insights about encounter processes between wildlife and watercraft. Our work emphasizes the importance of considering uncertainty when estimating wildlife mortality. Finally, our findings are relevant to other systems and ecological processes involving the encounter between moving agents

Monte_Carlo_Simulations.txt

This file includes R scripts to implement Monte Carlo simulations. It includes input information to reproduce results presented in the main text of the paper

Encounter_Rate_Expected_Mortality.txt

This file includes R scripts to estimate encounter rates and expected mortality. It includes input information to reproduce results presented in the main text of the paper and in Appendix S4

Correlated_Random_Walk_Simulations

This file includes R scripts to estimate encounter rates based on a simulation approach. It includes input information to reproduce results presented in the main text of the paper

Correlated_Random_Walk_Simulations

This file includes R scripts to estimate encounter rates based on a simulation approach. It includes input information to reproduce results presented in the main text of the paper