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Impact on marine species


Harbour porpoises (Phocoena phocoena). Photo: S. Gust
Harbour porpoises (Phocoena phocoena). Photo: S. Gust

Marine mammals in the North and Baltic Seas

The effects of impulse-like or permanent underwater noise pose a particular problem for acoustics-reliant whales and dolphins. The Habitats Directive prohibits any and all actions which could lead to the injury or death of specially protected species or which could cause significant disturbance to strictly protected species such as the harbour porpoise.

Impairment of hearing in harbour porpoises

Whales such as the harbour porpoises (Phocoena phocoena) that populate the North and Baltic Seas as highly reliant on their hearing. They use echolocation to find prey and a mate, and also to safely navigate the underwater world. Their hearing can be impaired by intensive noise occurrences (see: Impulse Noise) such those which arise with the use of air guns or marine construction projects. This can result in a temporary threshold shift (TTS) or a permanent threshold shift (PTS). Hearing damage can occur even when noise levels are below the hammer noise level reached in the construction of offshore wind farms.

Behavioural changes in harbour porpoises

The interactions between natural and anthropogenic noise can impair navigational and thus orientation ability in animals under water. Background noise can mask important acoustic signals. This masking can, among other things, make it difficult for animals to locate prey and communicate. It can also alter their social behaviour in that it can make finding a mate extremely difficult or even impossible.

In many cases, the only thing the animals can do is move to another area to escape the noise (scare effect). This draws on their energy reserves and can have fatal consequences for pregnant and nursing females who must invest huge amounts of energy in bearing and rearing their young.

Research on the impacts of underwater noise

Harbour porpoise with a data logger. Photo: J. Teilmann
Harbour porpoise with a data logger. Photo: J. Teilmann

BfN finances research into underwater noise as part of a large-scale research programme in the German EEZ of the North and Baltic Seas. A number of sub-projects look at how noise affects the hearing ability and behaviour of harbour porpoises (Phocoena phocoena) and grey seals (Halichoerus grypus). In addition, audiometric measures are taken and stress hormones measured in harbour porpoises following the use of an air gun in controlled noise input. The data logger stores information about water depth and swimming speed, the animal’s position and the surrounding noise (sounds made by the animal itself and other natural and anthropogenic underwater noise).

Impact of air guns and sonar equipment on whales

The use of air guns in seismic surveys and military activities affects marine mammals. Noise pressure from air guns can cause injury and death. Low-frequency sonar used in submarines and battle ships can lead to disorientation and can trigger flight reflexes in marine mammals – not without serious consequences. For example, it was found that beaked whales, whose blood contains extremely high levels of nitrogen, can develop the bends if they swim up to the surface too quickly after being scared by sonar input. They often become stranded as a result.

Other marine species

Animals which do not obviously rely on their hearing for survival can also suffer from the effects of noise.

Fish

The cuckoo wrasse (Labrus bimaculatus). Photo: S. Gust
The cuckoo wrasse (Labrus bimaculatus). Photo: S. Gust

Underwater noise can also affect fish. Studies conducted at the University of Bristol in the UK in 2011 showed that, in the fish studied, underwater noise leads to a significant lack of concentration which diminishes their ability to search for, find and take in food. The researchers also observed that the fish were more prone to ingest things that were harmful to their health.

Other effects of underwater noise that cannot be ruled out in fish include physiological damage (e.g. injury to their inner organs or rupture of their swim bladder). And as studies conducted at the University of Edinburgh showed back in 2005, fish larvae use sound to find protected reefs. If that sound is masked by background noise, it could impair fish larvae survival rates.

Cephalopods

Cuttlefish. Photo: F. Graner
Cuttlefish. Photo: F. Graner

In coleoidea, squid and octopus, researchers at the Polytechnic University of Catalonia in Barcelona, Spain, found evidence of serious trauma caused by noise. Their study published in 2011 showed that nerve fibres and fine sensory cells in the statocysts (small organs responsible for balance) are severely damaged by specific noise frequencies. As a result, the animals are unable to swim and their spatial orientation is impaired. Vital functions such as hunting, fleeing from scavengers and searching for a mate are made extremely difficult and even impossible over time because the damage caused to those sensitive organs cannot be repaired.

Shore crabs

Shore crab (Carcinus maenas). Photo: K. Wollny-Goerke
Shore crab (Carcinus maenas). Photo: K. Wollny-Goerke

In 2013, researchers at the University of Bristol in the UK published a study in which they showed that shipping noise can also cause stress in shore crabs (Carcinus maenas). Although the experiment was conducted under laboratory conditions and the animals got used to the ongoing noise over time, it cannot be ruled out that the constant coming and going of ships could cause shore crabs stress in their natural habitat. What is more probable, however, is that given the constant variability of underwater noise, the crabs suffer repeated exposure to stress.


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