Noise impacts on fish and invertebrates workshop

I spent last week in San Diego attending a workshop sponsored by the Bureau of Ocean Energy Management (BOEM) on the impacts of human generated noise on marine fish and invertebrates. Having watched the field of ocean noise impacts roll slowly forward in fits and starts for 20 years, this workshop is really a breath of fresh air (or a gulp of fresh water).

Most of what has driven the ‘noise impacts’ discussion over the years has been concern for marine mammals – both from regulations such as the Marine Mammal Protection Act and Endangered Species Act, and from the concerns of the public for the critters that are called “marine charismatic megafauna” in the conservation business.

Of course the ocean is much more than a menagerie of iconic animals; it also includes a vast portion of the biota – from the simplest bacteria and archea to the most complex communities of fish, invertebrates, and marine mammals – upon which all life on earth depends.

We have afforded a modicum of protection for some members of this menagerie with regulations because they inspire us or feed us. But our regulatory frameworks do not protect all of the animals which are impacted by noise and that make up the web of ocean life.

This is why the BOEM workshop was so exceptional. It brought together many of the world’s experts on marine bioacoustics to spend a few days digging down into our concerns and understandings about the impacts of noise on the less charismatic, but nonetheless equally important members of the animal kingdom found in the sea.

Giant squid beached coincident to seismic surveys

Giant squid beached coincident to seismic surveys

BOEM’s objective falls under the recent “ecosystem based management practices” advanced by NOAA Director Jane Lubchenko “to make non-arbitrary management decisions that are scientifically informed.” Our objective as attendees was to form a basis of understanding and inquiry that informs BOEM about impacts of noise on the diverse species of marine fish and invertebrates.

While this meeting did not solve all of the ocean’s acoustic mysteries, it provided a substantial opening to bring biologists, acousticians, physicists, and engineers together to work toward common strategies on understanding and decreasing our acoustical impacts on marine life.

After a decade of inaction on federal ocean policy, this is really something to celebrate.

Tracking walrus’ movement using only one ear

A recent paper was published by marine research firm JASCO on localizing walruses using a single hydrophone. The technique they have refined is detailed in the article and involves assessing “multipath signals” – echoes from the sea surface and seafloor – along with the direct signal to track the movements of walruses in the Arctic. This is remarkable because locating a sound source usually involves two or more receivers.

For example, all terrestrial vertebrates have two ears which allow us to locate sound sources. We do this using a number of different cues. One of the obvious cues is amplitude: if the sound is louder in one ear over the other we assume that the sound source is closer to the louder ear. Another more subtle cue is ‘time of arrival’ which allows us to locate a sound source by the difference between the times it takes for the sound to arrive at one ear and the other.

These two cues serve to give us a general bead on the horizontal source of a sound – whether it is to the left or right, in front of us or somewhere in between. This method is adequate for birds, frogs, and lizards in the context of their survival needs.

But we mammals have more complex localizing needs from sound so we have developed outer ears that provide us with more subtle cues – allowing us to determine things such as how close or far, and the height or azimuth of a sound.

Mammals with movable ears such as cats and horses can use their outer ears like periscopes to hone in on a source of sound. Primates such as us humans have fixed ears, so we derive location cues from secondary reflections off the pinnae of our ear.

It happens that all the whorls on our outer ears collect and reflect sound into our ear canal with a tiny time delay after the primary sound hits our ear drums. This is a bit like the “multipath” cues that JASCO teased out in their work (but with much less math).

These three cues – amplitude, time of arrival, and delay of the secondary reflection allows us to pinpoint the source of a sound with uncanny accuracy.

Of course marine mammals (with the exception of sea lions, polar bears, and otters) do not have outer ears. We know that they have equal, or even more complex localizing needs from sound, especially the Arctic animals that spend a good amount of time in the deep and dark waters of the Arctic winter.

It has been less than 100 years that humans have started to use sonar in marine environments. The folks at JASCO are rolling back sonar frontiers, showing us that complex data can be derived from single receivers.

Marine mammals such as whales and seals have been adapting to their acoustic environment for 20-30 million years. It stands to reason that these animals have evolved some pretty complex adaptations to sound perception.

Hopefully we can come to understand and learn from some of these adaptations before we cloud out their arctic environment with sounds to which they have not adapted.

Jasco graph describing walrus localization

BBC Focus on Sounds of the Sea

Yesterday BBC News put out a feature article on ocean acoustics. I suspect that this is really making the rounds because many folks have brought it to our attention. For good reason too, as it includes some great embedded sounds, references to other useful resources, and a couple of conversations with folks in the field, such as Chris Clark with Cornell Ornithology Lab, and Michel Andre whose “Listening to Deep Ocean” we covered in a January 2011 Newsletter.

It is encouraging that ocean bioacoustics is increasingly becoming “main-stream,” particularly in light of the fact that the reach of human noise is ever saturating into further reaches of the sea – requiring all of us to be better informed about how marine animals use their acoustic habitat, and how human noise is transforming it.

© Copyright Ocean Conservation Research - Theme by Pexeto