Beam Reach

Killer whale session at ASA meeting

Erica Beneze talks about clicks. (Note the reflection of co-author Jason, as well as session Chair David Mellinger.)

Beam Reach staff and alumni presented no less than six talks at the Acoustical Society of America (ASA) meeting held this week in Seattle. Setting a record that will be hard to beat, in one session on killer whale acoustics a full third of the 12 presentations involved Beam Reach! The talks ranged widely in their topics and methodologies (abstracts below). Bravo to the whole crew!

Three Beam Reach alumni were involved in this ASA meeting, up from one (Kenna Lehmann, fall 2007) at the 2008 ASA meeting in Paris.  Alumnus Erica Beneze (spring 2009) spoke about the relationship between the behavioral state of killer whales and their echolocation click rates and how it changes in versus out of areas proposed for marine protection. Alumnus Laura Madden (fall 2005) spoke first in a fisheries workshop session, comparing two ways to assess fish habitat restoration structures: non-invasive hydroacoustic methods versus the traditional electrofishing technique. Jason Wood and Peggy Foreman (fall 2006) asked whether the southern residents compensate vocally when ship noise increases using new recordings and ship track data from the Lime Kiln acoustic observatory maintained by The Whale Museum.

Val Veirs discussed ship noise signatures from a long-term study in killer whale habitat on Monday, and then introduced the concept of new underwater noise metric — the orca-weighted decibel — on Thursday.  Scott Veirs presented a model of killer whale signal masking by commercial ship noise (Prezi embedded below).

4pAB5. Masking of southern resident killer whale signals by commercial ship noise. Scott R. Veirs and Val R. Veirs

The endangered southern resident killer whales (SRKWs) emit sound to communicate with each other and to hunt fish. Communication or fishing are possible only within a distance R at which a signal can be detected.We determine detection distance by comparing the power spectra of the ambient noise and the received signal, with attention to the auditory response curve of the receiver. In Haro Strait, the center of the SRKW critical habitat, about 21 commercial ships per day, increases the ambient noise level by about 20 dB. To assess how ship noise may affect the SRKW communication and hunting, we define the fractional reduction in the zone of audibility at any location and time as the ratio of the area where signal detection is expected to occur in the increased noise regime to the maxi- mum detection area expected under ideal conditions R^2/Rmax^2. We map the decreased zones of audibility in Haro Strait during average and extreme ship noise by combining field measurements of spreading rates with source power spectra 1–100 kHz of common SRKW signals and typical ships.

1aABa8. Shipping noise signatures. Val Veirs, Scott Veirs, and Jason Wood

Throughout 2010, underwater recordings have been made of each ship passing two separate Haro Strait nodes of the orcasound.net hydrophone network. About 20 ships pass each day. Each ship has been identified in real time [automatic identification system (AIS)]. Measurements of received underwater noise levels and AIS variables are recorded as each ship passes the listening stations. Individual ships are observed multiple times moving in either northerly or southerly directions at times separated by a day or two and also by intervals of months. A database has been developed that contains the spectrum level of each ship 􏰃bandwidth 96 kHz at one location and 22 kHz at the other and the source level both in terms of intensity and angular distribution. Ship signatures in terms of frequency quantiles and angular distributions of emissions are quite reproducible. This database can be used to predict limitations on echolocating and vocalizing marine mammals’ active space due to specific ship noise emissions. In particular, predictions of marine mammal noise exposures in specific frequency bands can be made prior to specific vessels’ entry into an area opening the possibility of planning field observations to investigate correlations between behaviors and specific predicted noise exposures.

4pAB9. Are click rates in killer whales an indicator of group behavior and foraging hotspots? Erica L. Beneze, Jason Wood, Scott Veirs , and Val Veirs

Killer whales use sound to communicate, find food, and navigate through the ocean. Southern Resident killer whales are specialized hunters and predominantly target Chinook salmon. It is presumed that these whales use echolocation clicks to distinguish between different species of salmon and to navigate. If this is the case, then click rates should vary by group behavior as the need for locating prey and navigating change. It has also been suggested that certain areas are utilized heavily by this population for foraging (hotspots) and some of these areas have been included in NOAA’s proposed “no-go” zone. If click rates during foraging are distinct, then hotspots should be identifiable by click rates. This study tested if click rates varied by behavior state and geographic area. Group behavior was categorized into five states: foraging, traveling, milling, resting, and socializing. Click rate varied significantly by behavior state and by area. Socializing had the highest click rate followed by foraging, traveling, milling, and then resting. The Southern Residents had higher click rates in foraging hotspots.

4pAB6. Shipping noise and vocal compensation by Southern Resident killer whales: Haro Strait as a study case. Jason D. Wood (SMRU Ltd.), Peggy Foreman (Univ. of Washington), Val Veirs, and Scott Veirs

Southern resident killer whales (SRKWs) use acoustic signals to navigate, forage, and facilitate social dynamics. Researchers have published evidence that suggests SRKW compensate for increased background noise by increasing the source level and duration of their signals. Unpublished reports have also suggested that SRKW may compensate for background noise by repeating their signals and by preferentially using certain signal types. Most of this work has focused on noise from whale watching vessels or general background noise. Haro Strait is both the center of the summertime home range of the SRKW and an important shipping channel. From September 2009 to December 2010 almost 10 000 ships transited through Haro Strait with an average of 21 ships passing per day. Ship transits in Haro Strait can increase background noise by up to 20 dB and are detectable above back- ground noise for up to 30 min. This may be impacting the ability of SRKW to detect and utilize their acoustic signals. A five hydrophone array and Automatic Identification System receiver located at the Lime Kiln Lighthouse were used to record passing ships and SRKW in Haro Strait. This project investigates signal compensation strategies in SRKW in correlation with increased noise from passing ships.

4pAB7. Orca hearing weighted decibels: Underwater sound measurements appropriate to studies of Orcinus (killer whales). Val Veirs, David Bain, and Scott Veirs

In community noise studies, sound levels are usually measured under the dB-A weighting scheme, which was introduced 50 years ago in an effort to match noise measurements to the response of human listeners. Here we pro- pose an underwater noise decibel weighting scheme matched to the hearing sensitivity of killer whales (dB-O). This scheme is based on a convolution of the spectral energy of sound with the frequency-specific hearing detection thresholds of killer whales. The biological significance of noise sources may be more readily discerned if underwater sounds are quantified dB-O weighted. Further, use of this measure would emphasize the importance of broad-band measurement of noise rather than characterizing noise sources by the frequency with the peak power-spectral density and the source level of low frequency components. We compare the measures of representative noise sources, which have been recorded within the range of Southern Resi- dent Killer Whales, including small boats, ships, airguns, and mid-frequency sonar, using both flat and db-O weighted levels. While dB-O provides a more relevant characterization of noise than flat measurements e.g., for predicting noise-induced stress, more detailed measurements will be required to address masking of biological signals, whose frequency structure varies with type of phonation and direction.

4pFWa1. Evaluating freshwater habitat restoration with active acoustics. Laura E. Madden (School of Forest Resources and Appl. Res. Lab., The Penn State Univ.) and Jennifer L. Miksis-Olds (The Penn State Univ.)

The effectiveness of adding a submerged physical structure in order to increase fishery production is uncertain. Measuring fishery response to these alterations with conventional techniques is difficult. Electrofishing is a typical assessment method in freshwater fishery management and is often limited in sample size and sampling frequency. This study used active acoustic technology to evaluate the distribution and behavior of fish assemblages associated with added submerged rock structures in a reservoir currently undergoing habitat improvement. An acoustic water column profiler was deployed for three 1-week intervals at each of three replicate sites consisting of adjacent treatment areas with added rock structures and control areas without added structures. Electrofishing was conducted during each sam- pling interval. Fish abundance and behavior at each site were assessed from the volume backscatter time series and electrofishing data. Differences between areas with and without structures were compared. Combining acoustic technology with conventional assessment methods has enabled a more thorough evaluation of habitat restoration projects and helps guide the development of future conservation efforts.