Large filter feeders, such as baleen whales and basking sharks, could be particularly at risk from ingesting the tiny plastic particles, say scientists
Fiona Harvey The Guardian 5 Feb 17;
Whales, some sharks and other marine species such as rays are increasingly at risk from microplastics in the oceans, a new study suggests.
Species such as baleen whales and basking sharks, which feed through filtering seawater for plankton, are ingesting the tiny particles of indigestible plastic which now appear to permeate oceans throughout the world. Some of these species have evolved to swallow hundreds or even thousands of cubic metres of seawater a day, but taking in microplastic can block their ability to absorb nutrients, and may have toxic side-effects.
The new study, published in the journal Trends in Ecology and Evolution, advises more research on the megafauna of the oceans, as the effects of microplastics on them is currently not well understood. Scientists have found, for instance through examining the bodies of beached whales, large pieces of plastic in the guts of such creatures, but the effect of microplastics, though less obvious, may be just as harmful.
Elitza Germanov, a researcher at the Marine Megafauna Foundation and co-author the study, said: “Despite the growing research on microplastics in the marine environment, there are only a few studies that examine the effects on large filter feeders. We are still trying to understand the magnitude of the issue. It has become clear, though, that microplastic contamination has the potential to further reduce the population numbers of these species, many of which are long-lived and have few offspring throughout their lives.”
Many species of whale, filter-feeding shark and rays are already under threat from other problems, such as overfishing and pollution. The added stress from microplastics could push some species further towards extinction, the authors of the study warned.
One possibility is that the microplastics will convey toxins to the bodies of the megafauna, though this process is currently poorly understood.
Maria Cristina Fossi, a professor at the University of Siena and co-author of the study, told the Guardian that although there was no evidence currently that microplastics alone could kill filter-feeders, they could produce “sub-lethal effects” which would endanger their health.
She said research on whale sharks and fin whales had confirmed that filter-feeding species were exposed to toxic chemicals, perhaps through the breakdown of microplastics in their digestive systems. “Exposure to these plastic-associated toxins pose a major threat to the health of these animals since it can alter the hormones,” she said.
Plastic pollution: Scientists' plea on threat to ocean giants
Helen Briggs BBC 5 Feb 18;
Scientists say there needs to be more research into the impact of plastic pollution on sharks, whales and rays.
A study, in the journal Trends in Ecology and Evolution, says the creatures may be swallowing hundreds of tiny bits of plastic a day.
Microplastic pollution has the potential to further reduce the population sizes of the large filter feeders, they say.
Yet, there is very little research being carried out into the risks.
Researchers from the US, Australia and Italy looked at data on threats to large filter feeders from microplastics. These small plastic pieces less than five millimetres long can be harmful to the ocean and aquatic life.
The Gulf of Mexico, the Mediterranean Sea, the Bay of Bengal and the Coral Triangle are priorities for monitoring, according to a review of studies.
"The full magnitude of risks of ingesting microplastics are yet to be fully investigated," said Elitza Germanov of Murdoch University, Australia, and researcher at the US Marine Megafauna Foundation.
Possible risks include reduced nutritional uptake and damage to the digestive system when microplastics are ingested, she said.
In addition, toxin exposure through plastic ingestion could affect many biological processes, such as growth and reproduction, putting filter feeding populations "under even more strain", she added.
Flagship species
The study argues that large filter feeders, many of which are "charismatic and economically important species", should be prioritised for further research into risks from microplastics.
Filter feeders swallow hundreds of cubic metres of water a day to capture their food from water, and may take in microplastics during the process.
Microplastics are similar in size and mass to many types of plankton.
Studies have shown chemicals associated with plastics in the bodies of whale sharks and fin whales.
"Our studies on whale sharks in the Sea of Cortez and on fin whales in the Mediterranean Sea confirmed exposure to toxic chemicals, indicating that these filter feeders are taking up microplastics in their feeding grounds," said co-researcher Prof Maria Fossi of the University of Siena in Italy.
"Exposure to these plastic-associated toxins pose a major threat to the health of these animals since it can alter the hormones, which regulate the body's growth and development, metabolism, and reproductive functions, among other things."
Seven charts that explain the plastic pollution problem
Whale sharks feeding in the Sea of Cortez off Mexico's Baja Peninsula, which is an important breeding ground, are estimated to ingest under 200 pieces of plastic per day.
Fin whales in the Mediterranean Sea are thought to be swallowing closer to 2,000 microplastic particles per day.
The researchers say there have been reports of 800kg of plastic found in the carcass of a stranded whale in France and another in Australia contained six square metres of plastic sheeting as well as 30 whole plastic carrier bags.
The report highlights several key coastal regions for research and monitoring within the habitat ranges of the animals, including the Coral Triangle, the Gulf of Mexico, the Mediterranean Sea, the Bay of Bengal and other areas that have high microplastic concentration levels, such as the world's five oceanic gyres.
Whale sharks and other flagship species may act as a focal point for research, especially in countries that rely on wildlife tourism, say the researchers.
"It is worth highlighting that utilising these iconic species, such as whale sharks, manta rays and whales to gain the attention of and engage with communities, policy makers and managers will go far to enhance stewardship of entire marine ecosystems," said Ms Germanov, who is a PhD student at Murdoch University.
A number of filter-feeding sharks, rays and whales are on the edge of extinction. Many are long-lived and give birth to few offspring during their lives.
The whale shark, for example, is listed as Endangered on the IUCN Red List.
Found in tropical and warm temperate waters, it is the largest fish in the world, yet feeds on tiny plankton, crustaceans and small fish.
