By Elitza Germanov
I study the impacts of plastic marine debris on large filter-feeding fish. So far my research has been focused on manta rays, in field locations that have predictable, year-round aggregations. But the story is different for whale sharks. In my current research locations, I would be extremely lucky to catch a fleeting glance of a whale shark as they glide through the waters of Nusa Penida and the Komodo National Park (and I have not been so lucky yet), so to investigate their feeding grounds and assess the level of plastic pollution they are exposed to, I had to go and find where they gather to feed.
Fortunately for me, I got a good tip on a location not too far away from Bali. Seasonally, whale sharks aggregate and feed off the coast of North East Java. The waters are rich in plankton after the winds and rains of the north-west monsoons bring nutrients to the coastal waters. What I am interested in is if these same rains also bring trash to the feeding grounds and, if so, are the sharks also munching on the smallest of the plastic marine debris – microplastics?
Although this was my first time visiting the area and researching these giants, I was grateful to have the support from Dika Himawan, Whale Shark Indonesia leader, who has been studying the whale sharks here for over a year.
On a windy and rainy morning, typical of February weather in Indonesia, we headed out to the site to see how we were going to carry out our work and straight away our first challenge was presented to us. How would we be able to identify the sharks and obtain the data we need when the water visibility is less than one meter?
Unfortunately, this meant that we were unlikely to gather any additional data that could be submitted to whaleshark.org, a global database that uses spot and pattern recognition software to identify individual whale sharks. This powerful tool, with the help of data collected by citizen scientists around the world, can track long distance migrations, but would be of no use to us if we are unable to take a clear photograph of the sharks in the water.
Looking down from the top of the boat the sharks’ dorsal fins were easily spotted above the surface while they were feeding (as well as their heads and tails as they sucked the surface of the water). This gives us hope that by using other identification features, such as scars and notches, we will be able to at least identify these animals in the short term. This is part of the challenge of working with nature. As biologists, even though we may have already established protocols, we need to be able to adapt to nature to accomplish our research goals.
From our research, we hope to be able to estimate the levels of large and micro-sized plastic found in the whale shark feeding environment and the levels of plastic-associated toxins these sharks are exposed to.
As feeding volumes of whale sharks are over 300 cubic meters per hour, finding just one piece of plastic per cubic meter can quickly add up to potential ingestion of over 300 pieces per hour. Recent estimates for potential plastic ingestion by whale sharks in Mexico have reported that these animals may be ingesting approximately 170 plastic pieces per day.
With plastic also come nasty toxins that plastic sucks up like a sponge. While we still have a lot of work to do to analyze our data, we hope that our findings will show a clear picture of the woes these endangered gentle giants face. With Indonesia ranked the second worst marine plastic polluter in the world, we are concerned about this emerging large-scale threat. Whatever results our research may uncover, we hope it will serve to raise awareness about the animals that are most vulnerable to Indonesia’s plastic problem.