This week I came across an interesting review by Bauchi & Perry (2014) on the interaction of cetaceans and marine debris, most specifically plastics. Ingestion and entanglement of marine debris on cetacean species have been under reported, if you allow me to put it that way. But let me tell you, it’s not exactly anyone’s fault. You see, to verify the ingestion of debris by a cetacean, we depend on stranding events and although cetacean strandings can be common at certain times, they are most likely to be associated with other reasons than the ingestion of debris itself. Therefore, it is difficult to relate cause and effect. Stranded animals are usually very emaciated and it is extremely difficult to safely assert cause of death. These animals could strand due to multiple factors that do not always involve their current body condition. Their current body condition could be a reason for the stranding but it could also be a result of the stranding. Besides, to be able to evaluate a real impact on cetacean populations, we would need bigger sample sizes than what we get from strandings. Nevertheless, there is also the fact that a lot of strandings go unreported, not only by the local population, but sometimes by the authorities to the appropriate environmental body. But when they are reported, they can also be so late to the point that the animal is not suitable for necropsy anymore. To top up, sometimes necropsies are carried out in a way that data for plastics ingestion could be poorly collected if that is not the focus of the person conducting the necropsy.
All that is to say that yes, it is true, we have very few reports of cetacean encounters with plastic debris, especially when compared to other animals such as birds, for example. However, isn’t what we have so far enough to say there is an interaction and a negative impact? The above mentioned review attests so.
According to the review, debris ingestion has been reported for at least 56% of all cetacean species. The ingestion of debris can cause blockage or injury of the digestive tract, leading the animal to malnutrition and starvation. Debris ingestion can also impair the ability of the animal to float, feed or defend from predators. In addition to the physical impacts, toxic compounds which are added to plastic products to give them specific features such as durability or flexibility, for instance, can leach into the body of the animal and these compounds can also be biomagnified up the food chain. Another way that marine debris can impact cetaceans is via entanglement. The review states that at least 14 species of cetaceans have been reported to be found entangled in debris. Most of this debris is derelict fishing gear. It is however hard to tell if the fishing gear was derelict or active at the moment of entanglement and that is something that needs to be worked on to find out ways to distinguish active from derelict fishing gear when found.
Literature however fails to report ingestion of microplastics by cetaceans. Microplastics are <5mm bits of plastics that result from the breakdown by weathering of bigger pieces. Microplastics started to get more attention only recently and literature on the subject is peaking, though still in its infancy. Within the range of microplastics are synthetic fibres, which can be broken down during the washing of synthetic clothes, for instance, and also the microbeads. Microbeads are tiny spheres used in cosmetics such as facial scrubs and toothpaste. And although seen with the naked eye, nurdles or pellets, the raw material from which plastic products are made, once melted and shaped into user products, are also termed microplastics. It is supposed that filter-feeding animals are more prone to ingesting microplastics and since we are talking about cetaceans, baleen whales come to mind. A recent study (Fossi et al., 2012) has used phthalates to infer the presence of microplastics in baleen whales, as this is an additive (also known as plasticizer) used in plastic products. However, phthalates are used in the most diverse products and are known to be environmental pollutants, present in the air (as dust) and water and it is extremely hard to associate their levels to a single cause.
Despite the known gap in research, which is understandable and I am pretty sure it is being worked on (myself included), the review helps us to view more quantitatively the impact of marine debris on cetaceans and that allows us to look at it more critically and immediately know what could be done to improve our knowledge and research and awareness. As we say in Irish: bualadh bos 🙂
Dolphins at the Shannon Estuary, Ireland – Photo by Heidi Acampora
Published by Heidi Acampora