2. 1. Rutland Island
Rutland Island (11⁰20'00" N-11⁰32'00" N, 92⁰34'00" E-92⁰43'00" E) is one among the largest of the labyrinth group of islands in the southern region of the Andaman, separated by Duncan Passage from Little Andaman Island (Fig. 1). The island's total geographic area is about 120 Km2, with a shoreline of approximately 71 km. The study area has an estimated population of 347 people (Census 2011), with the primary occupations being farming and fishing. The study area is characterized by a tropical, hot, and humid climate with 3074.3 mm of rainfall on average per year. Besides, Rutland Island often encounters heavy gales, storms, and cyclones, unlike the rest of ANI’s (Goswami et al. 2020). The South-East Monsoon (SWM) brings substantial rainfall (76.35%) from May to September, followed by a short (22%) North-East Monsoon (NEM) from October to December, and a dry spell during the Pre-Monsoon (PM) between January and April (1.64%).
The study area receives minimum rainfall during the Pre-Monsoon as well. The wind speed would be 5 knots/hour in good weather conditions. However, during cyclonic storms, the wind speeds may exceed 120 to 130 knots/hour. The average annual relative humidity and air temperatures range is about 81%, and 23.9°C to 30.2°C respectively. Rutland Island experiences strong tidal currents ranging from 0.543 m/s (August) to 0.0109 m/s (April) due to the complex hydrological condition (https://marine.copernicus.eu). The study area also experiences semidiurnal tides (12hr and 20min), with mean wave heights of 1.90m and 0.5m during spring and neap tides, respectively. The tidal currents flow north to south during ebb tide and vice versa during flood tide. Due to the channels between the Labyrinth islands and cumulative effects of tidal range, strong surface currents are generated between 1) Rutland-Cinque Island (Manners Strait), 2) Twins island-Jahaji beach (Rutland), and 3) Labyrinth islands, South Andaman- Rutland (Mac Pherson Strait). As a result, the coastal waters around the study area are always turbulent.
The study area is a habitat for diverse fauna and an area of high biological productivity. Coral reefs, mangroves, sandy beaches, rocky shores, tropical evergreen forests, littoral forests, and deciduous forests exist within the study area. It also includes Mahatma Gandhi Marine National Park (MGMNP), established in 1983 to conserve varied fringing coral reef habitats and sea turtle nesting sites. The nesting ground of turtle species, saltwater crocodiles, and the Andaman water monitor lizard was commonly sighted in the study area and across the South Andaman Islands (Sivaperuman 2015; Samarasinghe et al. 2020).
2.2. Sampling strategies and macro litter survey
A macro litter survey (2.5cm to 1m) was carried out on thirteen sandy beaches on Rutland Island between February 2020 and March 2021. Three zones were established for the thirteen sandy beaches based on monsoonal currents. Katla Dera, Photo Nallah 1, Photo Nallah 2, Dhani Nallah, and Bakra Balu were all located in Zone I. Zone II included two beaches, Pharsa Dera and Machi Dera. Niranjan Balu, Kichad Nallah, Hathi level, Kumda Nallah, Bada Khari, and Jahaji were all included in Zone-III. The survey was conducted only under favorable weather conditions. The results were expressed as items per meter square for better understanding and comparison with earlier findings in India and worldwide. During the study period, a five-member reconnaissance team organized an orientation visit to each beach for planning the litter survey. Later, five members examined beaches with a coast length of less than 1 km in a day. On the other hand, a fifteen-member team inspected the beaches with more than 1km coastline in three to five days. The litters were counted, categorized (country-wise using the labels), and classified into six main groups (plastic, foam plastic, glass and ceramics, rubbers, cloths, and others) according to UNEP/IOC (Marine Conservation Society 2002; Cheshire et al. 2009).
2.3 Typology of macro litter
Several distinct litter types were distinguished according to material types and origin: plastics such as polyethylene terephthalate-PET (beverage bottles), packed drinking water plastic bottles, plastic buoys, foam buoys, engine oil jerry cans, polyvinyl chloride-PVC (toys and pipes), and fishing gears (ropes, nets, lures). The minor debris was the tube lights, light bulbs, liquor glass bottles, medicine glass bottles, cigarette lighters, toys, footwear, and toothbrushes. All litter items were counted individually.
2.4. Clean Coast Index
The data was compiled to assess the tidiness of the beach using the Clean Coast Index (CCI) (Alkalay et al. 2007) with minor modifications (instead of total plastic items, total litter items found on the beach were used).
CCI = (Total litter items on the beach/ Total area of the beach in Sqm) ×K
Coefficient K = 20 is a constant applied for statistical and convenience. According to the CCI, the following are the criteria: 1) 0–2: very clean-no litter observed, 2) 2–5: clean-no litter is witnessed over a large area, 3) 5–10: moderate-a few pieces of litter detected, 4) 10–20: dirty-much debris seen, 5) 20+: extremely dirty-most availability of litters on the beach.