A recent study combined a large sample of behavioral data from 16 satellite-tagged Cuvier’s beaked whales (Ziphius cavirostris) with concurrent records of Mid-Frequency Active Sonar (MFAS) use by military surface ships and helicopters in Southern California, and used a generalized additive mixed-effects model to predict that dive durations, surface intervals, and the duration between apparent foraging bouts increased with MFAS proximity. MFAS records used in the analysis were coarse; however, a subset of these data occurred when both the whale and transmitting platform were within the Southern California Anti-Submarine Warfare Range (SOAR), where high-resolution platform tracks and ping-by-ping acoustic records exist for many operations. We reviewed detailed circumstances surrounding the most extreme behaviors observed during MFAS to identify factors that might have influenced the response. As predicted by the initial study, the two longest deep dives (137.5 and 164 min) were exposed to ship and helicopter-deployed MFAS, respectively, at ~ 9 km. Short deep dives (< 45 min) were uncommon during MFAS (6 of 71), but those that did occur were all unusually shallow, at ~300-650 m above bottom depth. Long inter-deep-dive-intervals (IDDI, a proxy for foraging disruption) usually overlapped with MFAS, with the longest, lasting 541 min and 641 min, recorded during helicopter-deployed MFAS use at ~17 km and ~11km, respectively. Short IDDIs overlapping with MFAS were rare, though there were three under 45 min, all truncated by unusual deep dives. MFAS use was rare during both very long and very short surface intervals; however, there were two long MFAS-associated surface intervals (74-75 min) and four short (< 1 min), with MFAS as close as 7 km. We suggest the timing of sonar onset within behavioral events may be important and certain individuals may favor responses not typical of the population.
Citation:
Schorr, G., E. Falcone, S. Watwood, S. DeRuiter, A. Zerbini, R. Andrews, R. Morrissey, E. McCarthy, D. Moretti. 2017. Factors associated with unusually strong responses to mid-frequency active sonar in Cuvier’s beaked whales. Abstract (Proceedings) 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.