Passive Acoustic Monitoring

The following article deviates from my conventional posts about homemade water treatment, but it is an important issue in the environmental realm- and could give scientists a clearer picture of endangered species.

“Within the field of cetacean research, a passive acoustic monitoring (PAM) system can be defined as a set of acoustic and electronic devices aimed at detecting and tracking marine mammals by listening to their vocalizations” – Brunoldi, et. al.

Last month, I spent three days at the Louis Stokes Alliance for Minority Participation (LSAMP) conference in Indianapolis, along with many other dedicated researchers, motivational speakers, and even some graduate school survivors. A couple of students used passive acoustic monitoring (PAM) technology in their research on endangered species, which made me wonder: How else do we monitor endangered species? And how does PAM work?

Sounds of whales and boats from Stellwagen Bank National Marine Sanctuary.

PAM is different from sonar technology, which involves sending out echolocation pulses. Instead, scientists are receiving the echolocation pulses produced by animals and analyzing the sound’s characteristics in an attempt to individually identify animals. In other words, PAM picks up animal “voices”.

Historically, methods of population counting have had advantages as well as disadvantages, and would sometimes result in incorrectly labeling species as “extinct”.  There are four main methods of estimating wildlife population: complete counts, incomplete counts, indirect counts, and mark-recapture.

  1. Complete counts involve aerial views of the entire population through either a large group of surveyors or photography, and is typically very expensive.
  2. Incomplete counts entail counting the number of individuals in one area and extrapolating that number to represent the entire area.
  3. Indirect counts require evidence of a species’ presence, such as recording the amount of fecal matter, nests, or dens that an animal creates.
  4. Finally, mark-recapture methods are those we see frequently shown in wildlife reserves where individuals are tagged and monitored. In some cases individuals are recaptured after a specific period to develop the birth and death rate of the population.

Passive acoustics can be considered either an indirect count or an incomplete count. So far passive acoustic monitoring technology can only be used to record sounds up to 100 meters away. High frequency sounds also dissipate quickly. Nevertheless, passive acoustic monitoring is beneficial for monitoring species whose habitat is protected or difficult to traverse. The best part is that recording wildlife sounds, also known as bioacoustics, isn’t just for aquatic species. It can be used to monitor birds, too. There is an entire peer-reviewed journal from the UK dedicated to bioacoustics titled Bioacoustics – the International Journal of Animal Sound and its Recording.

Whales of the World by National Geographic.

I used to see inaccurate population counts as blessings. Researchers would announce a species as extinct, and people would understand the true consequences of over-hunting, deforestation, and urbanization. Twenty years later, the said species would be spotted somewhere completely unexpected, and faith was restored. It was like a second chance. Now, my view has shifted. I understand that as population counts become more accurate representations of the animal kingdoms that surround us, wildlife refuges can allocate resources to the particular species that truly are endangered and perhaps we can better protect the species that need protecting. What are your thoughts? Comment below 🙂

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