Why is sound such a vital tool in the marine world - and how do animals utilise this?
Importance of sound underwater
Sound is arguably the most efficient tool under the oceans surface, and marine mammals have evolved to utilise this potential. In a medium where sound travels better than any other modality, they use sound both actively and passively. Many use sound from natural sources for navigation and finding prey/avoiding predators, but have also adapted to use sound as a means for communication and sensing.
Examples:
Toothed whales use highly evolved and sophisticated echolocation to sense and track prey, alongside complex communications with members of their own species.
Baleen whales utilise long-range acoustic communication systems in social interactions and mating rituals. They can produce intricate songs that continue for several hours or days.
Bowhead whales use sound to initiate mating during the winter, and have been recorded singing 24 hours per day to attract a mate.
Narwhals use sound for echolocation for navigation and hunting, and roughly spend 27% of their lives using echolocation.
Humpback whales engage in songs for communication and socialisation.
Some dolphin species have behaviour-specific and signature whistles that can be distinguishable from other sounds.
Orca's (Killer whales) have cultural differences in their dialects, so different that we can actually distinguish between populations living in the same area.
Natural vs Anthropogenic Noise
The ambient (natural) background noise of the ocean varies at many different points. Waves, wind, ice, currents, even details such as water depth all dictate how loud ambient noise is. Anthropogenic sounds, as detailed in the Noise Pollution blog, are grouped into categories: (a) explosions, (b) ships and vessels, (c) airguns and seismic exploration devices, and (d) sonars.
Impacts of noise pollution on marine animals
A research team at the University of Victoria, Canada, analysed 42 studies from around the world on noise pollution and its effects on fish behaviour and physiology. They found that anthropogenic noise was the largest compromising factor in foraging, predator evasion and reproduction. Another study focusing directly on Beluga whales showed that they can lose hair cells in their ears when exposed to excessive noise.
Behaviour and physiological impacts are some of the largest consequences to anthropogenic noise, and so are detailed further in the Behaviour under the surface blog.
Monitoring, Conservation and Awareness
NOAA (The National Ocean and Atmospheric Administration) is a scientific agency in the United States that runs many studies and projects to protect the oceans. Their Ocean Acoustic's Program works closely with other governmental bodies studying and supporting research on anthropogenic impacts on marine animals. Their primary aims are to increase awareness of how marine animals use sound and how that is changing (for better or worse) based on human activities. They use passive acoustic techniques to compare how much ocean noise is increasing with human noise versus ambient sounds.
The Joint Nature Conservation Committee produced seismic guidelines in 1995, invoking thresholds and guidelines for sound sources such as pile driving and explosive use. These guidelines have since been replicated by multiple countries around the world.
The Cetacean Assessment and Ecology Program in Alaska establishes baseline information on marine mammals in Alaskan waters to make decisions about their marine resources.
The Pacific Islands Fisheries Science Center has a cetacean research program which uses a multitude of passive acoustic methods to monitor and assess the health and status of cetacean populations in that region.
Other scientific research programs:
- Ocean Acoustics Program
- The international Maritime Organisation
- The European Union
- The International Whaling Commission
- The Artic Council
- The Convention on the Conservation of Migratory Species of Wild Animals
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