March 11, 2020 — In the U.S., there are five populations of beluga whales, all in Alaska. Of those five, the Cook Inlet population is the smallest and has declined by about seventy-five percent since 1979. Subsistence hunting contributed to this initial population drop, but this practice was regulated starting in 1999, with the last hunt in 2005. Still, the beluga whale population in Cook Inlet has yet to recover. This population was listed as an endangered species in 2008, with hopes that the population would begin to recover in the near future, but more than a decade later they continue to decline, with a current population estimate of 328 whales.
Like other toothed whales, beluga whales rely highly on sound. They produce acoustic signals to find prey and to communicate; consequently, scientists can use acoustic recordings to study beluga populations and behavior. In 2008, the NOAA (National Oceanographic and Atmospheric Administration) Alaska Fisheries Science Center, in partnership with the Alaska Department of Fish and Game, put together an acoustic research program to continuously monitor beluga whale habitat. This program has two main objectives: (1) studying beluga whale behavior and population size, and (2) understanding the extent to which human-generated noise is disrupting beluga populations.
In the past, with raw audio recordings collected by underwater moorings, NOAA scientists used a very basic detector — based on energy levels in certain frequencies — to detect acoustic signals from beluga whales. This detector was tuned toward high recall, i.e., it was tuned to make sure that it didn’t miss any beluga sounds, but consequently allowed many sounds to pass through that were false positives, i.e. uninteresting background noise. Consequently, manual validation was required for each of those detections. This validation process is very time-consuming and labor-intensive, which limits the number of sensors that the team can deploy, and also limits the speed with which the team can provide answers to critical conservation questions.