title: Relationship between visual counts and call detection rates of gray whales (Eschrichtius robustus) in Laguna San Ignacio, Mexico.
abstract: Daily acoustic calling rates of Eastern North Pacific (ENP) gray whales were measured on 6 days during 1 mo of their 2008 breeding season in the sheltered coastal lagoon of Laguna San Ignacio in Baja California, Mexico. Visual counts of whales determined that the numbers of single animals in the lower lagoon more than tripled over the observation period. All call types showed production peaks in the early morning and evening with minimum rates generally detected in the early afternoon. For four of the five observation days, the daily number of "S1"-type calls increased roughly as the square of the number of the animals in the lower lagoon during both daytime and nighttime. This relationship persisted when raw call counts were adjusted for variations in background noise level, using a simple propagation law derived from empirical measurements. The one observation day that did not fit the square-law relationship occurred during a week when the group size in the lagoon increased rapidly. These results suggest that passive acoustic monitoring does not measure gray whale group size directly but monitors the number of connections in the social network, which rises as roughly M(2)/2 for a group size M.
authors.affiliation: Marine Physical Laboratory, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0238, USA.
authors.forename: Diana
authors.initials: D
authors.lastname: Ponce
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Thode
authors.forename: Melania
authors.initials: M
authors.lastname: Guerra
authors.forename: Jorge
authors.initials: J
authors.lastname: Urbán R
authors.forename: Steven
authors.initials: S
authors.lastname: Swartz
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D003625:Data Collection; D005260:Female; D008297:Male; D008800:Mexico; D008954:Models, Biological; D009622:Noise; D011156:Population Density; D012744:Sex Ratio; D013018:Sound Spectrography; D013997:Time Factors; D014828:Vocalization, Animal / Q000502:physiology*; D014907:Whales / Q000502:physiology*