[MARMAM] New Paper: Detecting changes in distribution of calling bowhead whales

W. John Richardson wjr at lgl.com
Sun Jun 17 08:17:25 PDT 2012

The following new paper describes a statistical approach suitable for analyzing effects of disturbance from a stationary sound source (in this case, an oil production facility) on the distribution of localized calls from migrating whales:
  McDonald, T.L., W.J. Richardson, C.R. Greene Jr., S.B. Blackwell, C. Nations, R.M. Nielson and B. Streever.  2012.  Detecting changes in the distribution of calling bowhead whales exposed to fluctuating anthropogenic sounds.  J. Cetac. Res. Manage. 12(1): 91-106.

  PDF copies are available from tmcdonald at west-inc.com or wjr at LGL.com  

  This paper includes approaches to deal with lack of statistical independence among repeated calls from the same individual whale or group of whales, variable call detection probability, and confounding effects of covariates.  On the expectation that the strongest disturbance effects would be on the closest whales, it uses quantile regression to assess effects on the proximal edge of the distribution of calls.  

  Previous related papers describe the fluctuating anthropogenic sounds (S.B. Blackwell et al., 2006, J. Acoust. Soc. Am. 119(1): 182-196); procedures for detecting and localizing the bowhead whale calls (C.R. Greene Jr. et al., 2004, J. Acoust. Soc. Am. 116(2): 799-813); and basic features of the bowhead migration as evident from the acoustic monitoring (S.B. Blackwell et al., 2007, Arctic 60(3): 255-270).  
Abstract:  This paper describes an analysis approach designed to detect the effects of fluctuating anthropogenic underwater sound on the distribution of calling bowhead whales (Balaena mysticetus) during migration.  The anthropogenic sounds in this case were associated with an offshore oil production island (Northstar Island) in the Beaufort Sea northwest of Prudhoe Bay, Alaska, but the method has wider applicability.  In autumn, bowhead whales migrate westward at varying distances offshore where some are exposed to Northstar sounds.  Anthropogenic effects, if present, were hypothesized to be most pronounced in the southern (proximal) part of the migration corridor.  Underwater sound levels were measured continuously ca. 500 m from Northstar, and locations of calling whales were determined by a seafloor array of directional acoustical recorders.  Weighted quantile regression related the 5th quantile of offshore call distance to anthropogenic sounds and other covariates.  Case weights were inversely proportional to both probability of detection and location uncertainty.  Due to potential dependencies in call locations, block permutation of uncorrelated whale call clusters was used to assign significance levels to coefficients in the quantile regression model.  Statistical model selection was used to determine the anthropogenic sound measures most correlated with the 5th quantile of offshore call distances, after allowing for natural within-season variation quantified by day-night changes, distance of the call east or west of Northstar, and date.  Data used to illustrate the method were collected over 29 days in September 2003 and included 25,176 bowhead calls.  The estimated offshore distance of the 5th quantile call was 0.67 km (95% confidence interval 0.31 to 1.05 km) farther offshore when tones associated with Northstar were recorded in the 10-450 Hz band during the 15 minutes just prior to each call.  The method has been applied successfully to similar data collected near Northstar in other years, and may be useful in other studies that simultaneously collect data on animal locations and fluctuating stimuli.
W. John Richardson
LGL Ltd., environmental research associates
e-mail wjr at LGL.com    web www.LGL.com
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