Monitoring fin and blue whales in the Lower St. Lawrence Seaway with
onshore seismometers
Abstract
The Lower St. Lawrence Seaway (LSLS), in eastern Canada, is an important
habitat for several species of endangered baleen whale. As we seek to
reduce the hazards that these endangered species face from human
activity, there is increasing demand for detailed knowledge of their
habitat use. Only a sparse network of hydrophones exists in the LSLS to
remotely observe whales. However, there is also a network of onshore
seismometers, designed to monitor earthquakes, that have sufficiently
high sample rates to record fin and blue whale calls. We present a
simple method for detecting band-limited, regularly repeating calls,
such as the 20 Hz calls of fin and blue whales, and apply the method to
build a catalog of fin and blue whale detections at 14 onshore
seismometers across the LSLS, over approximately a four-year period. The
resulting catalog contains >600000 fin whale calls and
>60000 blue whale calls. Individual calls are rarely
detected at more than one seismometer. Fin whale calls recorded onshore
appear to travel mainly through solid earth, rather than only entering
the earth at the shoreline, and they often have a complex
~2 s sequence of P-like and S-like phases. Onshore
seismometers provide a valuable, previously unused source of data for
monitoring baleen whales. However, in the LSLS, the current seismometer
network cannot provide high-precision whale tracking alone, so a denser
deployment of onshore and/or offshore seismometers is required.