Mario Rivera-Chavarria

The West Indian manatee is a threatened species throughout its known range. To improve its conservation, it is necessary to locate and count the individuals. This is a very difficult task due to the cryptic behavioral characteristics of the species and the environmental constraints, particularly in the Central American region, where muddy waters produce limited visibility. A method to estimate manatee population through vocalizations is an inexpensive, non-invasive, and novel option in the… Show more

The West Indian manatee is a threatened species throughout its known range. To improve its conservation, it is necessary to locate and count the individuals. This is a very difficult task due to the cryptic behavioral characteristics of the species and the environmental constraints, particularly in the Central American region, where muddy waters produce limited visibility. A method to estimate manatee population through vocalizations is an inexpensive, non-invasive, and novel option in the region. Digital signal processing techniques are proposed to denoise and detect manateevocalizations in field recordings. Also, a feature extraction and selection is performed together with the expectation maximization algorithm to estimate the number of individuals from a set of manateevocalizations. An F-measure of 0.90 is achieved using the detection method over 345 manatee calls. All calls are correctly classified and the exact number of individuals is estimated using the individual recognition method over 54 calls of four manatees. Show less

The Antillean manatee (Trichechus manatus manatus) is an endangered marine mammal that inhabits the Caribbean Sea and riverine systems in Central America. Their acoustic behavior is relevant for individual identification, mating and parental care. Manatees produce tonal sounds with highest energy in the second harmonic (usually 5 kHz), and their audiogram indicates sensitivity from 0.3 kHz to 90 kHz with lowest thresholds in the 16 to 18 kHz range. We recorded manatees in the San San River, a… Show more

The Antillean manatee (Trichechus manatus manatus) is an endangered marine mammal that inhabits the Caribbean Sea and riverine systems in Central America. Their acoustic behavior is relevant for individual identification, mating and parental care. Manatees produce tonal sounds with highest energy in the second harmonic (usually 5 kHz), and their audiogram indicates sensitivity from 0.3 kHz to 90 kHz with lowest thresholds in the 16 to 18 kHz range. We recorded manatees in the San San River, a highly polluted riverine system in Panama, using a stereo array. Frequency transmission experiments were conducted in four subhabitats, categorized using riverine vegetation. Incidental interactions of manatees and small motorboats were examined. Acoustic transmission was linearly related to tonal vocalization characters: correlations were stronger in freshwater than in transition and marine environments. Two bands, 0.6 to 2 kHz and 3 to 8 kHz, attenuate similarly in all subhabitats, and these bands encompass F0 (tone) and peak frequency respectively of manatee tonal calls. Based on our data we conclude that frequency transmission depends mainly on river depth and bottom characteristics, also motorboat sounds mask signals from 3.5 kHz to 8 kHz, which overlaps the peak frequency of tonal calls. In spite of differences between acoustic transmission in subhabitats of the San San River, manatees utilize bands that transmit efficiently in all subhabitats. Show less

Sciaenid passive acoustics are a demonstrated valuable tool for fisheries management. In spite of this, an efficient software tool to detect and identify fish sounds is not currently available. Such tool would be useful for autonomous recognition and array methodologies. For Neotropical environments this lack is even more conspicuous since the availability of corroborated sciaenid sounds is limited. We are developing such tools using corroborated Cynoscion squamipinnis (Pisces: Sciaenidae)… Show more

Sciaenid passive acoustics are a demonstrated valuable tool for fisheries management. In spite of this, an efficient software tool to detect and identify fish sounds is not currently available. Such tool would be useful for autonomous recognition and array methodologies. For Neotropical environments this lack is even more conspicuous since the availability of corroborated sciaenid sounds is limited. We are developing such tools using corroborated Cynoscion squamipinnis (Pisces: Sciaenidae) sounds. Our approach is based on timbre statistics, short and long-term partial loudness, and the 30 Hz typical pattern found on the signal's stridulations. Relevant fish drums are detected through empirically found fix thresholds for the timbre statistics and the 30 Hz pattern, and a dynamic threshold established by an unsupervised algorithm based on the long-term loudness. Current results show a recognition rate of 80%. Despite these promising numbers, there are still challenges ahead. In the future, we plan to incorporate other variables that affect underwater sound characteristics such as depth, source level distance, and physical chemical properties, which may be crucial to make a user friendly, accurate, and practical tool, for neotropical marine environmental managers. We also plan to extend this method to other soniferous coastal fish. Show less

We present a method to automatically identify sound emissions produced by sciaenid fishes, and in particular by Cynoscion jamaicensis. This species' sound emissions typically have a 24 Hz pulse repetition rate and a quasi-harmonic pattern can be appreciated in spectra, which produces a pitched quality in the sounds. The proposed method is based on long-term partial loudness, pulse repetition rate, pitch strength, and timbre statistics. Current results show an F-measure of 0.9.

Rivera Chavarría, Mario. 2012. Odontoscion xanthops Gilbert, 1898 (Pisces: Sciaenidae) sounds as reef disturbance indicators. Brenesia, Volumen 2012, Número 78:74-77

Although it has been hypothesized that reef fish reduces sound production during extreme environmental events, it is possible that fish sounds are still present but only masked by elevated environmental noise. Although available acoustic technology makes it difficult to address this question, we can still generate hypotheses about the impact of environmental noise on fish sound production. Is there a behavioral response to environmental noise, or are fish sounds present at the same levels but… Show more

Although it has been hypothesized that reef fish reduces sound production during extreme environmental events, it is possible that fish sounds are still present but only masked by elevated environmental noise. Although available acoustic technology makes it difficult to address this question, we can still generate hypotheses about the impact of environmental noise on fish sound production. Is there a behavioral response to environmental noise, or are fish sounds present at the same levels but masked and therefore undetectable without adequate filters? We recorded sciaenid (Pisces: Sciaenidae) sound production around Isla Tortuga, Costa Rica, during the "Nortes," a period of strong winds caused by cold fronts and extreme variation of atmospheric pressure. Sciaenid sounds apparently stopped with almost no emissions during strong winds (56 miles∕h) and transitioned to the normal emission rate on the next day when winds receded to 2 miles∕h. We hypothesize that fish sounds were present at all times, but masked by wind-produced noise instead of a biological modulation as described by Mann and Grothues (2009) in similar conditions. I present circumstantial evidence in support of this hypothesis and discuss possible methods to test it directly. Show less