Investigating the relationship between large scale oceanographic features and the presence of marine mammals in the Gulf of Alaska
The purpose of this study is to use a multiyear acoustic data set from the Gulf of Alaska (GOA) for sperm whales and other odontocetes, to determine potential seasonal occurrence patterns and examine the relationship between these patterns and environmental drivers.
Sperm whales are one of the most widely distributed marine mammals. Whaling has had a huge impact on their population so in the US, the sperm whale is listed as endangered species. However, the current population status for the N. Pacific is largely unknown. Especially at inaccessible areas like offshore the GOA and during winter season the rough weather conditions don’t facilitate visual surveys to study marine mammals.
Sperm whales produce loud, broadband and highly directional echolocation clicks that can be detected from several km away and that makes them well suited for passive acoustic monitoring. Even though there is a plethora of studies on sperm whales, it still remains unclear what oceanographic factors drive their distribution. Acoustic data were collected at the Ocean Station PAPA, located far offshore the GOA. The PAPA station is part of the Ocean Sites Network that provide us one of the oldest oceanic time series with a buoy that continuously measures a large variety of oceanographic parameters. This study area is of special importance being located at the south of the Navy’s training exercise area.
The hydrophone used, the PAL, was designed at the Applied Physics Laboratory of the University of Washington by Jeffrey Nystuen. It’s not a continuous recorder, it rather functions as an event detector that saves acoustic samples that contain transient sounds, like the biological signals are. It samples at 100 kHz and is deployed at around 200m depth where the bottom depth is more than 4Km. Using a 5 years long dataset we intent to identify odontocete vocalizations and then by using characteristic acoustic features like interclick interval and spectrum features we classify different species. Seasonal occurrence patterns derived and oceanographic measurements are used to evaluate the environmental drivers of the whales’ distribution. The ultimate goal is to understand potential effects of climate change to their populations and support conservation efforts.