Ships strikes are a persistent threat for large whales worldwide, but one that can be challenging to quantify due to ocean currents, carcass decomposition, and the propensity of some large whales to sink after death. While persistent mortalities due to ship collisions have been observed off the US west coast, they represent a fraction of the overall threat. The coast off southern California is highly productive which results in high whale abundance. Is also hosts internationally designated shipping lanes leading to and from the ports of Los Angeles and Long Beach, one of the busiest port complexes in the world. Due to this elevated risk, a system aimed at reducing ship strikes, Whale Safe, was developed by the Benioff Ocean Initiative. Whale Safe combines three data streams to assess whale presence in the region: visual observation information, habitat modeling predictions, and near real-time acoustic monitoring. This is the first time these three complementary data streams have been combined for the assessment of whale presence, serving as California’s first near real-time, automated whale notification system.
Acoustic monitoring system in Whale Safe relies on a moored buoy deployed in the Santa Barbara Channel. The buoy consists of a float with satellite transmitter and a bank of batteries used to power the underwater recorder deployed on the ocean floor. The recorder, digital acoustic monitoring (DMON) instrument, records the data continuously in addition to implementing an on-board detection and classification algorithm. The algorithm is used to extract time-frequency contours (pitch tracks) of signals of interest, which get relayed to shore via a satellite link, along with classification information. This information is reviewed daily to determine if any of the pitch tracks are whale calls. Each 15-minute period is classified based on having detections, possible detections, or no detections of endangered blue, fin, and humpback whale calls. Level of acoustic whale occurrence is determined based on the percent of 15-minute periods that have one or multiple species of whales present. This acoustic whale metric is combined with the other data streams to estimate the overall daily whale presence rating as: low, medium, high, or very high.
In the first year of deployment, Whale Safe system resulted in a one month extension of the duration of NOAA’s voluntary speed reduction zone in the area. Due to the persistent presence of blue whale and other acoustic detections into the fall of 2020, this speed reduction scheme that usually ends on 15 November was extended in 2020 to 15 December.