A statistical acoustics approach for estimating population-scale bowhead whale migration speed and direction

Area of Science:

• Marine biology
• Bioacoustics
• Animal migration

Background:

• Assessing bowhead whale migration patterns is challenging due to low individual vocalization rates.
• Passive acoustic monitoring is often impractical for tracking individual whale movements.

Purpose of the Study:

• To develop and apply a statistical method for inferring population-level migration speed and direction.
• To analyze bowhead whale fall migration from the Beaufort Sea to the Bering Sea using acoustic data.

Main Methods:

• Utilized a network of vector sensors deployed off the Alaskan North Slope (2008-2014).
• Generated call density time series from distinct acoustic zones.
• Cross-correlated call density sequences between zones to determine travel time and speed.

Main Results:

• Consistent westward migration speeds of approximately 5 km/h were observed across multiple sites and years.
• Detected less prominent eastward movements and occasional week-long shifts in migration speed.
• Method proved effective regardless of zone separation distances (3.5 to 15 km).

Conclusions:

• Acoustic cross-correlation of call density provides a robust statistical method for estimating whale migration parameters.
• Bowhead whales exhibit predominantly westward fall migration with some variability in speed and direction.
• This approach overcomes limitations of tracking individual animals in large-scale migrations.