Uses and Challenges

Mar 1

Photo by Rob McClelland (2019), Channel Islands, CA

Energy, Data, and Money

Certain audio recorders are limited by energy source and data storage (Küsel et al 2016). Continuous recording requires a greater amount of power and storage depending on how long your study needs to run. Continuous recording also generates larger files, which means more work to sort usable recording from unusable recording. Storage and management for audio data collected can be an issue as the higher the quality, the bigger the file and the more data to manage (Pijanowski et al, 2011). If you are considering having multiple recording devices across a broad range, Pijanowski et al (2011) recommend having a system set in place to remotely access data and to power recorders via some alternate form of energy such as solar or wind that is renewable and can be generated at its data collection site.

While Pijanowski et al (2011) mark high expense as a past limiting factor, Blumstein et al (2011) mentions declining prices. Whytock & Christie (2017) express that small scale studies are low cost while larger studies (requiring more recorders) are of course more expensive. It seems all aspects from the microphone, the software used to analyze the recordings, the computer boards, the memory cards, etc. all either exist in low-cost versions or are decreasing in price as technology advances.

The Environment

Another consideration for audio recorders is environmental conditions. While weather plays a serious role on land, water proofing is crucial in ocean studies (Küsel et al, 2016). If any leak occurs, all data can be lost and the technology can be damaged. In the ocean, audio recorders for passive acoustic monitoring need to be attached to objects that can withstand the challenges of the ocean (water, salinity, pressure, currents, etc). These objects can include gliders (Küsel et al, 2016) as well as buoys and stationary platforms (André, 2014). If your recorder is set to collect data on a memory card, and the glider is misplaced, so are all of your audio recordings. In addition, “hardware malfunctions” are harder to fix here until after the object is retrieved (Küsel et al, 2016). However, these uses of passive acoustic monitoring have a very low impact when recording marine mammals and don’t contribute massive amounts of noise to the already teaming soundscape (André, 2014).

Photo by Rob McClelland (2019), Reef Check, Channel Islands, CA

Photo by Rob McClelland (2019), Isla Guadalupe, Mexico

Distance and Frequency

When looking at an ecosystem, everything (wind, waves, ships, rain, animals, etc.) makes noise, but at all sorts of different frequencies (Lindseth & Lobel, 2018). For example, while snapping shrimp are at a high frequency, whales click at much lower frequencies (Lindseth & Lobel, 2018). In prime conditions, these low frequencies can be picked up >100km away by some audio recorders (André, 2014). However, if individuals make sounds past this distance, or if they are not making sounds in that space, they will not be picked up (Küsel et al, 2016). When individuals are within that distance and making clicks, having more than one recorder can allow you to calculate directionality of individuals making sound (Küsel et al, 2016). Lindseth & Lobel suggest audio recordings in the lab should be taken in conjunction with recordings taken in the field to “definitively describe” vocalizations within species that are not already thoroughly documented. While previous studies have used video to make this verification, water clarity can be an impeding/inhibiting factor.

Spectrograms

Audio recordings can produce “spectrograms”, which are graphs of sound showing frequency and intensity through time. Marine mammals, as well as birds, can be identified by these spectrograms (Pijanowski et al, 2011). Sometimes, glitches can mimic marine mammals in the spectrograms, and requires “close inspection” to parse out (Küsel et al, 2016). While trained scientists inspect recordings to identify sounds and species, in certain cases, software can be used to identify potential “calls of interest” (Küsel et al, 2016).

Framework

While much of the soundscape ecology field is new, there has not been ample time to streamline the framework. Sugai et al (2019) expresses the need for the development of cross-study sampling procedures, methods, and protocols to provide consistency across studies using passive acoustic monitoring. “As the field continues to grow, it is recommended that studies continue to use multiple parameters, each of which provides details about different aspects of a soundscape [75]. Determining which indices provides the most accurate description of the acoustic data, and by extrapolation biological patterns, remains one of the major challenges in soundscape ecology.” (Lindseth & Lobel, 2018).

Anna McClelland