The number of stranded marine mammals with marine debris such as plastic and nets found in their stomach is on the rise. Last week, a shocking finding of a 100 kg litter ball in the stomach of a stranded sperm whale went through the news. Earlier this month, we covered the story about a juvenile sperm whale washed ashore in Wales with plastic sheets and ropes in its stomach. In spring, two separate cases of young stranded whales have been found with several pounds of plastic in their digestive system. And almost exactly one year ago, the necropsy report of several stranded sperm whales in Germany was published, linking their deaths to “stomachs full of plastic and car parts” as we stated here. Additionally, many stories covered strandings due to entanglement like the case of these two baleens whales in Orkney or this report by the Natural History Museum in the UK.
But macroplastic is not the only problem. Researchers recently examined seven beluga whales in Canada. Their findings of microplastics in the digestive systems of the whales further supported the global pollution problem. The issue of increased plastic pollution in the marine ecosystems is a well-known fact. But the extent of its impact on the marine wildlife is still not clear.
We know that macroplastic is one of the main threats for all marine mammals, as entanglement can lead to decreased mobility and potentially fatal injuries. But toothed whales can also mistake it for prey, thus ending up in their stomach. Since it cannot be digested, the marine debris accumulates there, decreasing the space for actual food or even obstructing the bowels. Stranded marine mammals with plastic in their digestive system are often emancipated and weak. The ingested debris can also lead to inner injuries, decreasing the animal’s strength further.
Microplastic, on the other hand, poses an immense threat to the baleen whales. They filter thousands of cubic meters of water every day, catching the small particles in their baleens. This filtering process is initially meant to trap the massive amounts of krill the whale feeds on. But even these tiny organisms tend to mistake the plastic for prey and ingest it. By feeding on contaminated organisms, the big whales consume masses of microplastic every day. Those particles might be too small to obstruct the animal’s digestive system, but they are being absorbed in the animal’s tissue instead. Over time, this bioaccumulation can reach toxic levels, leaving the big animal prone to weakness and disease. A study of the Royal Society Open Science even suggested that baleen whales are in “potentially greater danger from plastic pollution that from oil” due to the plastic’s affinity to the baleens.
We still do not know about the extent of plastic and debris in our oceans. But with the increase in affected marine mammals stranded on our beaches, its bad impact is strikingly obvious. Nevertheless, the ones washed ashore are only the tip of the iceberg. Many more whales and dolphins are suffering and dying unseen underneath the surface with plastic in their stomach.
The fact that these big animals at the top of the food chain are suffering “shows that our marine ecosystems in general are in peril”. Suffering of smaller fish are often overlooked by casual observers and their quick decomposition means they are rarely investigated. If we want to preserve the ocean’s health, we need to see the bigger picture and start paying attention. Suffering marine mammals are just the start. But “even for casual observers, a dead whale blocking a beach vacation photo is pretty hard to ignore”.
The mechanisms and consequences of plastic in marine mammals are more detailly explained in this article: https://www.vox.com/2019/5/24/18635543/plastic-pollution-bags-whale-stomach-beached
The mentioned study by the Royal Society Open Science can be found here: https://royalsocietypublishing.org/doi/10.1098/rsos.182194
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