Crustaceans need ears too!

A preponderance of marine bioacoustic work has been focused on marine mammals – whales, dolphins, and pinnipeds. This is in large part due to the “charismatic megafauna” paradigm where big, complicated animals with recognizable expressions attract most human interest.

While fish – particularly large or colorful species can capture our attention under this same rubric, most scientific research on fish is advanced due to their commercial importance. Critters further down on the ‘charisma scale’ even while equally complicated in their adaptations are typically not studied, so it was great to hear OCR pal and Biologist Erica Staaterman’s presentation on mantis shrimp at the recent “Acoustic Communication by Animals” Symposium.

Even better was that her work was picked up by “Science Daily” and distributed to a wider public.

The mantis shrimp are visually intriguing; being some 8” to 10” (and up to 15”) long with a pair of incredibly complicated eyes that can sort out twelve colors and reconcile polarized light. Some species visually communicate by modulating fluorescence on their bodies, and some species live in monogamous pairs for up to 20 years!

With all of these attributes it is likely that vision is their dominant perceptual adaptation, but Erica found that they also communicate with sound through a low frequency rumble or purr. In the realm of human perceptions this isn’t Grammy material, but when pitch-shifted up an octave the call and response patterns become more apparent.

She also found that listening to the shrimp was very different in the wild from listening to them in a tank. The shrimps’ communications were, “so synchronized they sounded like a chorus.”

We can only speculate what they are expressing with these sounds, but Erica’s work has rolled back just a little more of the mystery of the deep. [Read Ocean-Noise post on ‘chorusing’]

Her paper was published in Aquatic Biology.

Acoustic Communication by Animals

Photo by "mali mish" on Flickr

Photo by Joe Shlabotnik on Flickr

I’ve just returned from a conference on “Acoustic Communication by Animals” at Cornell University. This was sort of a “vacation conference” for me as it was attended by a broad cross section of bio-acousticians outside of the usual marine mammals and fish folks found in the ocean noise-oriented meetings. With specialists in bats, birds, insects, frogs, hearing physiology and neurology etc., the meeting allowed me to indulge in my generalist predilections; in this case with a presentation on “chorusing.

Chorusing is usually defined as “acoustic signaling produced collectively by a group of individuals whose activity is clustered in both space and time… which may be temporally structured in alternating or synchronous formats.” The point of my paper was to expand the definition to:

Individual response to signals generated by another or other individuals within a group context that unifies the group in an aggregate behavior.

The reasoning behind this expanded definition is to move the discussion  outside of the usual “individual animal’s breeding and territory needs” and into a context of animals behaving as “acoustic communities.” I’m advancing this because I feel that animals subject to the impacts of human enterprise are much more than “bags of protein with behaviors” or “input devices” – definitions by which they often seem to be evaluated. This broader definition also helps explain the stunning flock behavior of starlings and equally stunning schooling behavior of sharks and forage fish.

In the presentation I qualify both of these behaviors as acoustically stimulated “spatial chorusing.” If you take an individual fish or bird out of these “choruses” and put them in a lab they cease being complete animals. While they are easier to evaluate as specimens, much of what community animals do – and how they are potentially compromised in their habitat by our actions – is lost in translation.

I believe that the aggregate behavior of an acoustic community can tell us much more about species vulnerabilities as well as resilience to human generated noise. Without this consideration we may be missing some opportunities.

Communication signals threaten marine habitat

Commnuication and navigation beacons.

Back in the mid 1970’s Physical Oceanographer Walter Munk was evaluating the acoustical transmission characteristics of the ocean “sound channel” – an isothermal layer in the deep ocean that baleen whales use for long distance communication.

His visionary work in this field developed into a 1991 experiment called the “Heard Island Feasibility Test” which produced the first sound that was literally heard around the world – under water.

The utility of this ocean feature for long distance communication was something Dr. Munk had been advancing ever since 1978 when he proposed a “Sea Net” – an acoustic based ocean internet system that could be used – and heard around the world.

It was along this trajectory that the “Acoustic Thermography of Ocean Climates” (ATOC) was proposed, and then deployed in 1992 despite the misgivings many of us had about projecting very loud sounds throughout the entire Pacific Basin.

ATOC turned out to be relatively benign, but for me it was the harbinger of things to come; where all manner of acoustic signals would be used for research, military, and industrial communication –crowding out the important bio-acoustic signals of marine animals.

The signals and technologies continued to develop, and it was in 2000 with a US Navy proposal of a long distance sonar system called “SURTASS” (which would ensonify the entire ocean with military noise) that the public became aware of the problem.

Public hearings were conducted, lawsuits filed, and demonstrations ensued. It was in the midst of this gambit that the Bahamas Stranding occurred – alerting us all that despite the assurances of our Navy that there was indeed a problem.

It is the continuous association between military operations and marine mammal strandings that has kept the Ocean Noise Pollution issue in the public conversation. While most of this conversation orbits around military sonar and seismic surveys, the exponential advance of other acoustical communication and navigation signals threatens to seriously compromise the marine bio-acoustic habitat.

This link describes one such signal, but there are many others being developed and deployed for research, industrial, and military applications.

While some of these signals may not be pernicious – even while overlapping some odontocete communication and bio-sonar bands, it would be good to know this prior to saturating biologically significant habitat with sounds generated by expensive equipment.

Tools to make this determination is one of OCR’s banner projects which we hope to complete this year pending support from funding agencies.

When we do complete these tools it will be none too soon, as underwater communication systems are springing up like mushrooms all over the sea.

Stay tuned!

Report from the May 2009 Acoustics Society meeting

Density of two months of large commercial vessel traffic in the sanctuary, with peak densities seen in the shipping lanes

Density of two months of large commercial vessel traffic in the sanctuary, with peak densities seen in the shipping lanes

“Thrilling” is not a word I thought I would ever use in describing an Acoustical Society meeting, but there were moments last week that bordered on just that. Driving this is an intersection of rapidly increasing computer processing power and advancing sensor technologies – put in the hands of some of the nimble intellects that are making up the current crop of bio-acoustic post-docs.

Over the five days of the meeting there were many sessions on “Passive Acoustic Monitoring” (PAM) which presented many of the aspects of putting sensors in the ocean, collecting the data, and then making sense of it all. In practice this often means collecting the vocalizations of whales or dolphins over a period of time and watching the population dynamics change as a consequence of environmental conditions.

The output of these studies can be time-compressed animations of the peregrinations of dolphin schools or whale pods,[i] or in the case of Chris Clark, the acoustical impacts of ship traffic on humpback, fin and right whales.[ii] Dr. Clark’s animated display was a stunning “spatial-temporal” graphic of the changes in the hearing and communication range of these three whale species as a cargo ship passed over their habitat. I will make these graphics available on the OCR website once I get them from Chris, but meanwhile you can find out about the program here:

Another telling presentation by Manolo Costellote came from his PAM study of the seasonal migration of fin whales in the Mediterranean Sea over a three year period. During one of the seasons there happened to be a concurrent seismic airgun survey. The monitoring clearly demonstrated that the whales avoided their traditional winter feeding areas throughout and even after the survey. This indicates the acoustical impacts of airgun surveys reach over hundreds of kilometers for these animals.

Of course Manolo wanted to know where the surveys were taking place, and something about the sizes of the airgun arrays. He managed to locate the company doing the work, but they were predictably uncooperative. Not to be discouraged, he did a little sleuth work and found a “blog” of one of the crew members, which included the entire equipment list; airgun capacities, photographs of the ship, and pretty much everything he needed to calibrate his findings except for the exact locations of the survey (which he derived through some clever data evaluation).

It is work like this which may eventually put the current practices of airgun surveys “on the ropes” until the oil industry can find more benign ways of locating offshore oil.

Many other breakthroughs were presented and new ideas introduced over the course of the week across the field of acoustics. While overall the meeting was still pretty high on the “pencil-pocket” index, our field of marine bioacoustics is going through a thrilling sea change.

Stay tuned!

[i] Kaitlin E. Frasier “Acoustic tracking of whistling dolphins offshore of Southern California”

[ii] Christopher W. Clark “Result ad insights from operational monitoring networks”

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