NoiseTracker: Tracking vessel noise and its implications for Southern Resident killer whales in the Salish Sea

Executive summary

Underwater noise is a primary threat limiting the recovery of critically endangered Southern Resident killer whales (SRKW). Degraded acoustic conditions can reduce communication efficiency and foraging success, with potential consequences for body condition, fecundity, and survival. In response, several mitigation measures have been implemented within SRKW habitat in the Salish Sea, including seasonal Vessel Restricted Zones (VRZs) and a voluntary commercial vessel slowdown program. This study evaluated long-term changes in underwater noise and SRKW occurrence in the Salish Sea over the past decade using hydrophone data from Pender and Saturna Islands. We quantified changes in vessel-related noise across biologically relevant frequency bands and compared acoustic trends with SRKW detection records and vessel traffic data from 2017 to 2025. 

Results indicate a sustained degradation of the acoustic environment, with consistent increases in underwater noise across all metrics and frequency bands relevant to SRKW. Despite existing management measures, these increases correspond with rising vessel traffic and changes in vessel composition and operation. Current management measures appear insufficient to offset cumulative vessel noise exposure in critical SRKW habitat, highlighting the need for more effective, enforceable, and biologically relevant reduction targets.

Glossary

Acoustic habitat: the sound environment that surrounds marine animals, characterized by typical noise levels and patterns.

Auditory masking: when a loud or overlapping sound makes it harder for an animal to detect or recognize another important sound. This happens because the interfering sound raises the level at which the quieter sound can be heard, or the “threshold” at which the second sound becomes noticeable, a process known as masking. For marine mammals, this can interfere with their ability to communicate, find food, or detect danger, for example, masking a call from a calf, an echolocation click or the sound of approaching prey

Broadband sounds: sounds that contain energy across a wide range of frequencies simultaneously. Examples include whale songs, breaking waves, or ship noise. Broadband noise can mask multiple types of marine mammal sounds because it overlaps with many frequency bands. 

Decibels: a unit for measuring sound intensity on a logarithmic scale, where small increases in dB represent large increases in actual sound energy. Underwater acoustic uses a difference reference pressure than airborne acoustics (1 µPa versus 20 µPa respectively), meaning decibel values for underwater sounds are not directly comparable to those reported for sounds measured in air.

Decidecade band: A standardized frequency interval used in underwater acoustics to measure and compare sound levels. The full range of audible frequencies can be divided into broad intervals called decades (each spanning a tenfold increase in frequency, e.g., 100 to 1,000 Hz). A decidecade is one-tenth of such an interval, providing a finer-resolution slice of the frequency spectrum. Decidecade bands allow consistent, detailed comparisons of noise levels across studies and are commonly used to characterize underwater noise across biologically relevant frequency ranges..

Echolocation: the natural sonar system used by dolphins, whales, and other marine animals to navigate and hunt by producing sounds and interpreting the echoes.

Excess Noise: the increase in underwater sound levels attributable to vessel activity above baseline environmental noise conditions. Excess Noise is calculated by comparing periods with detected vessel noise to temporally adjacent natural conditions to estimate vessel-driven increases in sound levels.

Frequency:  the number of sound wave cycles that pass a given point per second, measured in Hertz (Hz). Low frequencies (few cycles per second) produce low-pitched sounds; high frequencies (many cycles per second) produce high-pitched sounds. In underwater acoustics, frequency is biologically relevant because different marine animals produce and hear sounds within specific frequency ranges.  For example, Southern Resident killer whales use frequencies roughly between 0.5 and 100 kHz for communication and echolocation. One kilohertz (kHz) equals 1,000 Hz.

Listening Space Reduction (LSR): a measure of how much vessel noise reduces the acoustic space available to killer whales relative to baseline conditions, expressed as a percentage. LSR was calculated within the 0.5-15 kHz SRKW communication band.

Quiet Time: the proportion of time during which no detectable vessel noise is present, expressed as a percentage of total recording time (%). 

Sound Pressure Level (SPL): a standardized physical measure of the pressure fluctuations caused by a sound wave, expressed in decibels (dB). SPL allows consistent comparison of sound intensity across different environments and studies. 

Spectrogram: a visual representation of sound showing frequency (Hz) over time, with intensity typically represented by colour or brightness.

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