Why Whales and Dolphins are Eating Plastic – New Insights
Why have so many whales and dolphins been found in recent years with their guts packed with plastic? Is this only because of horrifying amounts of plastics in their ocean habitats or are there other factors at play? Recent research provides some new insights and illustrates again the terrible damage that plastic wastes cause.
Over recent years, numerous stranded whales or dolphins (collectively known as cetaceans) have been found with remarkably high levels of plastic wastes in their alimentary canals. In some cases, these materials are known to have contributed to the deaths of the animals concerned. The plastic items include portions of rope, netting, plastic sheeting, plastic bags and bottles. This has led to much speculation about why the animals concerned are ingesting this alien material.
Plastic ingestion – a lethal habit
Deep diving species, mainly beaked and sperm whales, are among those most affected and so one theory is that the areas where these animals were feeding are so highly polluted with plastic wastes that they simply could not avoid ingesting it with their prey (for example, deep sea schooling squid), and especially as they are suction feeders. The poor animals could simply be accidentally sucking in the plastics along with their prey.
Another possibility was that they actually enjoy chewing on the plastic materials and then ingested them as a by-product of this play behaviour. There is a famous film for example of a young sperm whale chewing on an old plastic bucket, which is eventually taken away from it. This was shown in one episode of the BBC series, Blue Planet II and, generally, there is no doubt that many cetaceans play with natural and unnatural objects that they find in their environment, and this may put them at risk of ingesting these items.
Neither of these theories can be completely ruled out and certainly the ubiquity of plastics in deep water feeding habitats must play a role in their ingestion but recent research has now found what seems likely to be the primary driver for this aberrant and life-threatening behaviour. These animals hunt for their prey using their remarkably acute sense of hearing and a new study shows that the acoustic profiles of degraded pieces of plastic in their environment are very like those of their prey. Hence, they may in fact be simply mistaking pieces of dangerous plastic for squid or fish – because to them they sound the same – and then eating them believing them to be prey.
Matching acoustic profiles
The research was conducted by a team of researchers at Duke University in the USA. They compared the acoustic ‘target strength’ of squid and squid beaks with naturally weathered and fouled plastics from the North Carolina coastline. They found that 100 % of the plastic debris tested had ‘either similar or stronger acoustic target strengths’ compared with that of the prey items, concluding that their findings supported “the hypothesis that consumption of plastic by deep-diving odontocetes is driven by a misperception of acoustic signals”.
Plastics in cetacean breaths
A further recent piece of research has confirmed the presence of microplastics (tiny pieces of plastic) in the blow (the exhalations) of bottlenose dolphins sampled in Sarasota Bay in Florida and Barataria Bay in Louisiana. This, sadly, confirms, that the airways of these animals are contaminated with this material. In humans, inhaled microplastics can cause tissue damage and inflammation potentially leading to disease and these is concern now that dolphins may be affected in the same way.
Addressing the plastic pollution threat
OceanCare has been campaigning for many years to address the many threats posed by plastic pollution to our environment, ecosystems and wildlife. It is deeply disturbing to now hear that cetaceans in their dark deep undersea world are eating plastic in mistake for their prey with sometimes lethal consequences. This is an unexpected consequence of plastic pollution, there may be others.
The ubiquity of plastics, including microplastics, is truly disturbing.
From November 25 to December 1 the fifth and final session of the Intergovernmental Negotiating Committee (INC) to develop an international legally-binding plastics treaty to end plastic pollution, including in the marine environment will take place in Busan, Republic of Korea.
OceanCare has been involved in this process since it first began, and we will be there at this meeting too, to address the issue of plastic pollution along the entire lifecycle of plastic. We will be a voice for the cetaceans and all the living beings now living in a world filled with plastic pollution.
We need a comprehensive, ambitious and effective treaty that addresses this terrible threat in all its stages and to reduce production of virgin plastics, use and release into the wider environment.
Scientific information
The new paper about the acoustics of plastics can be found here.
For a recent review of the interactions between cetaceans and plastics go here.
The study of microplastics in dolphin breaths is discussed here.
