An Ocean Growing Louder by the Decade

Since the mid-20th century, low-frequency ambient noise levels in the world's oceans have increased dramatically — driven primarily by the global expansion of commercial shipping. Some acoustic monitoring studies suggest that background noise in major shipping lanes has risen by roughly 10–15 decibels over the past 50 years. In the underwater world, where sound is the primary medium of communication, navigation, and hunting, this transformation has profound consequences.

The Main Sources of Human Ocean Noise

Commercial Shipping

The global commercial fleet numbers in the tens of thousands of vessels, each generating continuous low-frequency noise from propellers, engines, and hull vibration. Shipping lanes often overlap directly with critical whale habitat — feeding areas, migration corridors, and breeding grounds. Because ship noise falls in the same frequency range as the long-distance calls of baleen whales (roughly 10–500 Hz), it directly masks the very signals whales use to communicate and find mates.

Military Sonar

Mid-frequency active sonar, used by navies for submarine detection, emits intense sound pulses that can cause significant harm to cetaceans. Several mass stranding events have been temporally and spatially linked to nearby naval exercises, particularly affecting beaked whales. The proposed mechanism involves a form of decompression-like injury triggered by panic responses to the sonar signal, causing whales to surface too rapidly from depth.

Seismic Surveys

Oil and gas exploration uses air guns — devices that release bursts of compressed air to create sound pulses that penetrate the seafloor and reveal subsurface geology. These blasts, repeated every 10–15 seconds for days or weeks, produce some of the loudest human-generated sounds in the ocean and have been documented disrupting whale behavior, communication, and feeding over very large areas.

How Noise Affects Whales

The impacts of noise pollution on cetaceans span a spectrum of severity:

  • Masking — Background noise covers up acoustic signals, reducing the effective range over which whales can communicate. A blue whale's calls that once carried hundreds of kilometres may now only reach a fraction of that distance.
  • Behavioral displacement — Whales may abandon important feeding or breeding areas in response to persistent noise, reducing their access to critical resources.
  • Stress responses — Studies have found elevated stress hormone levels in whale feces collected from areas with high shipping traffic — a physiological indicator of chronic stress.
  • Acoustic adaptation — Some populations have been documented shifting their call frequencies or increasing call amplitude ("Lombard effect") to compensate for noise — a costly evolutionary pressure.
  • Physical injury — Acute exposure to intense sounds (sonar, air guns) can cause direct tissue damage, hemorrhage, and disorientation.

What's Being Done

Encouragingly, ocean noise is one of the more tractable threats to whale conservation because it can be reduced relatively quickly with policy and technology:

  1. Vessel speed reductions — Slowing ships even slightly can reduce propeller noise significantly. Voluntary slow zones in critical habitat have shown measurable acoustic benefits.
  2. Propeller and hull design — Quieter propeller designs and hull smoothness improvements can dramatically reduce chronic shipping noise.
  3. Seasonal routing adjustments — Shifting shipping lanes around known whale feeding and migration areas reduces acoustic overlap at critical times.
  4. Seismic survey restrictions — Some governments have introduced "soft start" procedures and exclusion zones, though campaigners argue these measures fall short of what's needed.
  5. International frameworks — The International Maritime Organization (IMO) has issued non-mandatory guidelines for reducing underwater noise from shipping, with ongoing pressure to make these binding.

The Urgency of Acoustic Conservation

For species like the North Atlantic right whale — of which fewer than 360 individuals survive — any additional stressor can tip the balance toward extinction. Reducing ocean noise is not a marginal concern; it is a fundamental part of giving threatened whale populations the space and silence they need to find each other, feed, breed, and recover.