Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8322
Title: The relationship between vessel traffic and noise levels received by killer whales (Orcinus orca)
Author: J. Houghton, Marla M. Holt, M. B. Hanson, Deborah A. Giles, Candice K. Emmons, Jeff T. Hogan, Trevor A. Branch, G. R. Van Blaricom
Publication Year: 2015
Journal: PLoS ONE
Keywords: noise, whale watching, vessel traffic, vessel impact, killer whale, southern resident killer whales,noise,Whale Watching,vessel traffic,vessel impact,southern resident killer whales,killer whales

Whale watching has become increasingly popular as an ecotourism activity around the
globe and is beneficial for environmental education and local economies. Southern
Resident killer whales (Orcinus orca) comprise an endangered population that is
frequently observed by a large whale watching fleet in the inland waters of Washington
state and British Columbia. One of the factors identified as a risk to recovery for the
population is the effect of vessels and associated noise. An examination of the effects
of vessels and associated noise on whale behavior utilized novel equipment to address
limitations of previous studies. Digital acoustic recording tags (DTAGs) measured the
noise levels the tagged whales received while laser positioning systems allowed
collection of geo-referenced data for tagged whales and all vessels within 1000 m of
the tagged whale. The objective of the current study was to compare vessel data and
DTAG recordings to relate vessel traffic to the ambient noise received by tagged
whales. Two analyses were conducted, one including all recording intervals, and one
that excluded intervals when only the research vessel was present. For all data,
significant predictors of noise levels were length (inverse relationship), number of
propellers, and vessel speed, but only 15% of the variation in noise was explained by
this model. When research-vessel-only intervals were excluded, vessel speed was the
only significant predictor of noise levels, and explained 42% of the variation. Simple
linear regressions (ignoring covariates) found that average vessel speed and number
of propellers were the only significant correlates with noise levels. We conclude that
vessel speed is the most important predictor of noise levels received by whales in this
study. Thus, to aid recovery efforts, measures are needed that reduce vessel speed in
the vicinity of killer whales.

Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Characterize the interaction of human use and habitat distribution, quantity and quality.