title: A comparison of acoustic and visual metrics of sperm whale longline depredation.
abstract: Annual federal stock assessment surveys for Alaskan sablefish also attempt to measure sperm whale depredation by quantifying visual evidence of depredation, including lip remains and damaged fish. A complementary passive acoustic method for quantifying depredation was investigated during the 2011 and 2012 survey hauls. A combination of machine-aided and human analysis counted the number of distinct “creak” sounds detected on autonomous recorders deployed during the survey, emphasizing sounds that are followed by silence (“creak-pauses”), a possible indication of prey capture. These raw counts were then adjusted for variations in background noise levels between deployments. Both a randomized Pearson correlation analysis and a generalized linear model found that noise-adjusted counts of “creak-pauses” were highly correlated with survey counts of lip remains during both years (2012: r(10) = 0.89, p = 1e-3; 2011: r(39) = 0.72, p = 4e-3) and somewhat correlated with observed sablefish damage in 2011 [r(39) = 0.37, p = 0.03], but uncorrelated with other species depredation. The acoustic depredation count was anywhere from 10% to 80% higher than the visual counts, depending on the survey year and assumptions employed. The results suggest that passive acoustics can provide upper bounds on depredation rates; however, the observed correlation breaks down whenever three or more whales are present.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Thode
authors.forename: Lauren
authors.initials: L
authors.lastname: Wild
authors.forename: Delphine
authors.initials: D
authors.lastname: Mathias
authors.forename: Janice
authors.initials: J
authors.lastname: Straley
authors.forename: Christopher
authors.initials: C
authors.lastname: Lunsford
mesh_terms: D000162:Acoustics; D000818:Animals; D005398:Fisheries / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D010473:Perciformes; D011235:Predatory Behavior / Q000502:physiology*; D013018:Sound Spectrography; D050661:Sperm Whale / Q000502:physiology*; D014741:Video Recording / Q000295:instrumentation / Q000379:methods*; D014828:Vocalization, Animal