Written by: Renee Street – Our Amazing Friend, PADI Course Director, and Big Time Ocean Lover
It is not breaking news that our oceans are filled with plastic. Nor is it breaking news that many marine species are affected. But, a new study, focused solely on sharks and the results are yet another cause for concern and call to action.
Plastic In Our Oceans
It is estimated that between 4.8 and 12.7 million tons of plastic enter the oceans each year. A large portion of marine plastic debris is microplastics (plastic particles less than 5mm) which have been found in all marine environments.
Microplastics come from everyday items like cosmetics, polyester clothing, and, more commonly now, hygiene products such as face masks. Once in the ocean, they can float on the surface, remain in the water column, or accumulate on the seafloor. As a result, ingestion by marine species has become very common.
Microplastics have been found in turtles, marine mammals and many fish species. But microplastics in elasmobranchs (sharks and rays) have been largely understudied.
This new study examined four species of shark: small-spotted catshark, starry smooth-hound, spiny dogfish (pictured below), and the bull huss, which were captured as bycatch in a local fishery in the United Kingdom. An examination of the digestive tracts of these sharks found that 67% contained microplastics. A total of 379 microplastics were found in 46 sharks with one shark, a bull huss, having 154 fibers in its stomach and intestines. The study found that larger sharks contained more microplastics. Interestingly, the relative amount did not vary by species despite their differing habitats and prey.
It is not known how the sharks ingested the plastic although there are two possible avenues. First, through their food source which may have ingested the plastics prior to consumption by the shark. Second, through sediment which can be ingested when feeding. Another interesting note is that there have been multiple studies of bony fish in the same geographic region which found plastic ingestion rates across species between 1-47%; significantly lower than in the sharks.
Further study is needed to determine exactly how these microplastics might impact the health of sharks but evidence of microplastics in other marine creatures has been shown to negatively affect feeding behavior, development, reproduction, and life span.
Where Is All This Plastic Coming From?
A 2015 study found that the top five countries contributing to marine plastic debris are all in Asia: China, Indonesia, Philippines, Vietnam, and Sri Lanka. Indonesia, our home country, is responsible for over 3.2 million metric tons of mismanaged plastic waste and at least 1.29 million metric tons of that ends up in our oceans.
These numbers are from 2010, which likely means that today’s numbers are significantly higher.
Little By Little, A Little Becomes A Lot
We are doing our part to ensure that we aren’t contributing to Indonesia’s plastic problem both by increasing awareness of alternatives to single-use plastic and reducing the amount of plastic used on the Gili Islands. Check out our Plastic Free Paradise campaign!
We are also trying to help remove debris that has already found its way into the ocean. We are proud to have Adopted a Dive Site, Meno Slope, in the Gili Islands we work weekly to remove marine debris and report it to our partner, Project AWARE.
While no single action can end the marine debris problem, studies like this one help to educate people on the size of the problem and its consequences, and will hopefully continue to lead to small actions by all of us as well as larger actions by governments around the world.
To read the complete study as published in Nature, click here.