It is estimated that in the UK alone local authorities spend an average ~ £6000 per km per year (Mouat et al., 2010) on cleaning ports, harbours and areas of touristic importance; generating a growing interest in the use of mechanical devices to facilitate clean up. But while mechanical interventions are increasingly suggested as a means of removing plastic litter from aquatic environments; their performance is rarely evaluated.
Researchers from the International Marine Litter Research Unit set out to investigate the performance of the Seabin - a “trash skimmer” created for calm sheltered environments, such as marinas, ports, and yacht clubs - within a tidal marina location in Plymouth.
The Seabin was installed at 50.364233 and −4.131958 at Queen Anne's Battery marina between 21 April and 26 June 2021. Queen Anne's Battery marina sits within Plymouth Sound (Southwest UK) which is influenced by a semi-diurnal tide and temperate tidal ecosystems as well as heavy marine traffic and commercial and recreational boating activity (Langston et al., 2003) being a site of six marinas and western Europe's largest naval base. The Seabin was placed in an area where floating marine litter congregated and in a location that did not interfere with the marinas boating activities. A seaward facing wall and pontoon either side of the device protected it against strong wave action.
Manual versus mechanical cleaning
Staff at four marinas in Plymouth were asked a series of questions regarding their cleaning operations in order to draw further comparisons between mechanical devices and conventional manual cleaning approaches. The questions focused on the method, frequency and extent of cleaning operations, the size, composition, and extent of litter retained, and the cost of such operations. An approximate cost of these manual cleans were assessed and based upon the frequency, duration and litter retention (assuming a standard salary rate, depreciation, and age of vessels used and estimates of litter removed if accurate record not kept) compared with the Seabin.
Lastly, an estimate was made as to the number of Seabin devices that would be required to keep Queen Anne's Battery marina ‘free’ from floating litter, based upon litter density in the marina and the litter removal rate recorded by the Seabin.
When discussing study data results the following variables are taken into consideration:
- Seabin selectivity and performance during variable weather conditions.
- Retention of marine life.
- Average mass and average abundance of litter collected with operation time.
- Seabin function in variable weather conditions.
- The influence of Seabin devices on floating marine litter vs. other cleaning approaches.
- The experiences of end users in other locations.
- Current manual cleaning efforts in Plymouth marinas.
This study provides the first formal independent evaluation of the performance of the Seabin device.
Further evaluations of mechanical devices designed to intercept plastic litter flow in coastal environments are necessary to help indicate the efficacy of mechanical cleaning solutions for the removal of litter from the marine environment and inform key policy interventions such as the UNEA 5.2 Plastics Treaty.