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.
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.
KEYWORDS: ACOUSTICS; ARCTIC; BOWHEAD WHALE; MIGRATION; MODELLING;
MONITORING; MOVEMENTS; NOISE; SURVEY-ACOUSTIC
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