Page 50 - January 2006

Standards News
WORKING GROUP ON PASSIVE ACOUSTIC MONITORING STANDARD
Aaron M. Thode
Marine Physical Laboratory, University of California, San Diego La Jolla, California 92093-0238
Members of the Working Group who were at the ASA Meeting in Minneapolis. Left to right: Aaron Thode, James Miller (standing), David Mellinger, Jeremy Nedwell (stand- ing), Ann Bowles, and Edmund Gerstein. Note that we need YOUR help. You are missing from the meeting and the photo.
It has been known for decades that many marine animals make underwater sounds ranging in frequency from 10 Hz to over 100 kHz. Associating various sounds with spe- cific species has been an active research topic to which mem- bers of the Acoustical Society of America (ASA) have made substantial contributions. A good start on this topic can be found in Reference 1 or by consulting the Macaulay Library of Sounds at Cornell University (http://www.birds.cornell.edu/macaulaylibrary/). Many researchers now focus their efforts to study under what behavioral, geographical, and seasonal circumstances an individual from a given species will produce a sound. For example, sperm whales (Physeter macrocephalus) produce a vocalization called a “coda,” which is a series of 3-10 clicks
2,3
arranged with a certain rhythm . Recording from groups of
sperm whales across the globe has shown regional variations
4,5,6
in coda activity . It is unclear at this point whether coda
differences can be used to describe genetically distinct popu- lations. In general there remain many uncertainties about the use of passive acoustic monitoring (PAM) for detecting individuals or estimating marine animal population sizes. For an example of one of the most successful attempts at acoustic censusing see Reference 7.
Despite these uncertainties, there have been many efforts over the past two-decades to use PAM as a tool to comple- ment visual observations as a means to detect the presence of marine mammals in areas where high-impact anthropogenic activity is underway, defined here as “mitigation.” The use of PAM methods, which typically involve towing a two- or three-element passive array a few hundred meters behind a ship, has spread beyond the research community and is now
being used by various government agencies, non-govern- ment organizations, and consultants. Several industry seg- ments are actively pushing for the development and imple- mentation of PAM procedures for marine mammal mitiga- tion. One of the most active proponents of PAM has been the seismic exploration industry, which often uses arrays of devices called airguns to produce high-amplitude impulses that are used to image sub-seafloor structure by recording the
1,8,9 reflected and refracted returns on passive hydrophones .
In June 2005 the ASA Standards committee formed a working group to determine whether certain implementa- tions of PAM technology have matured enough to warrant the development of an American National Standards Institute (ANSI) standard. The first meeting of the working group took place on October 19, 2005 during the 150th meet- ing of the ASA in Minneapolis, to begin discussions and draft a purpose and scope for a possible standard.
Based on comments from the seven people who attend- ed the meeting, the following statements were drafted to explain the rationale behind the proposed standard.
(1) To establish a set of minimum procedures that would enable a technical nonspecialist to increase the likeli- hood of acoustic detection of a marine animal vocaliza- tion, if such a vocalization is made. The nonspecialist may not have been responsible for the selection of the equipment provided. Thus this standard stresses proce- dures, not equipment.
(2) To define a set of data archiving, documenting, and reporting procedures so results and conclusions from
48 Acoustics Today, January 2006