In partnership with Ozeankind, Chumbe Island successfully carried out four beach clean ups, over the period of November and December 2020.
For these clean up events, the Chumbe Clean Up team introduced a systematic method of collecting and recording washed up marine litter with which our team was able to establish a baseline dataset for Chumbe Island that we can continue build up over time.
The method involves buddy teams who are collecting and recording litter along pre-defined transects (see demarcations of all 8 transects in picture). The collected litter is then sorted into three categories (glass, metal, plastic), weighted accordingly and then picked up by Chumbe’s partners Zanrec and Chako for recycling.
This approach allows us to analyse how much litter the ocean currents are bringing to the island, where the hotspots of accumulation are, as well as composition and origin of the litter. We can find out more about litter origin with the help of product bar codes if they are still present: The first 3 barcode digits represent an international code and describe where the product has originated.
As November and December lie in the season of short and heavy rainfalls and increased windspeed, we expected that litter from urban centres will be washed into the ocean in higher numbers than during other months. For Chumbe, this would mean that with every high tide, increased amounts of litter are washed up from two directions: from Dar es Salaam in the South-East or from Stone Town in the North-West.
This is what we found:
- In total, we collected 95,5 kg of marine litter across all four clean up events.
- Most of the litter was collected during our first beach clean up on 16th November. After that, we found stable but slightly decreasing amounts of litter.
- When comparing the east coast and the west coast, we found that the total weight washed up at the Chumbe shores was evenly distributed.
- In Transect 1, we found a total of 17,2 kg of broken glass and glass bottles with plastic caps during our first clean up. That was the biggest catch we made in all transects and all four clean ups.
- We think that this hotspot of litter accumulation may also be due to the geomorphological formation of the Bahari Breeze bay that lies in Transect 1. It acts like a catch basin for incoming currents and litter.
- When looking further into the individual categories of litter, we can see that the West coast is more heavily littered by glass items, whereas the litter at the East coast is dominated by plastic litter. This may also be explained by the weight of the different categories: While lighter, more volatile plastic items get washed up in the sheltered Zanzibar-facing coast, at the West coast, only the more heavy glass and metal items overcome the stronger ocean currents.
- Whenever possible, we also analysed the origin of marine litter. This is possible when an item still holds a label that includes a barcode. While most items that could be identified were plastic drinking bottles associated with producers from the East African region, some items were identified to have more distant origins:
- Most abundant item collected: Plastic Drinking Bottles
- The item that travelled the longest: A metal tin for lubricants from the United States