Contribution of social media to cetacean research in Southeast Asia: illuminating populations vulnerable to litter

Marine debris is defined as any persistent manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment (Galgani et al. 2010). Plastics are typically the main component, accounting for approximately 60 to 80% by volume (Moore 2008), most of it derived from mismanaged waste from land (Jambeck et al. 2015). Plastic contamination of the marine environment was first reported in the 1960s and has significantly increased over recent decades (Ryan 2015). Due to its persistence and buoyancy, marine plastic can disperse great distances, and as a result has been detected worldwide in all major marine habitats (Moore 2008). Its ubiquitous presence is of increasing concern due to the negative consequences it has on marine ecosystems (STAP 2011). Although marine plastic has been commonly observed across all oceans (Ryan 2015), there is a vast amount of spatial variability. Southeast Asia is the third most populous geographical region globally with 70% of its human population living in coastal areas (Bryant et al. 1998). Coastal settlements, along with massive industrial development, contribute towards the large volumes of plastic released into the marine environment, often transported there by rivers, drainage systems or wind (Todd et al 2010). Six countries in this region are listed in the top 20 that mismanage their waste worldwide, with on average 79% of waste, primarily plastic, ending up in the ocean (Jambeck et al. 2015). Southeast Asia is a global centre of marine biodiversity, with many species suffering significant declines in recent years (Yamakita et al. 2017). However, marine plastic research in the ASEAN region (defined as Indonesia, Vietnam, Thailand, Singapore, Malaysia, Philippines, Cambodia, Laos PDR, Myanmar, and Brunei Darussalam (asean.org)) is still in its infancy. Five out of the ten ASEAN member states have no published studies on the ecological and environmental impacts of marine plastics (Lyons et al. 2019). Data on the sources and quantity of plastic waste are lacking, highlighting a need for urgent risk assessment and the identification of hotspots of plastic pollution to help mitigate release into the ocean (Lasut et al. 2018).

Marine megafauna (defined as marine mammals, seabirds, marine and estuarine reptiles, and large fish such as billfishes, sharks and tuna) are particularly vulnerable to plastic pollution (Provencher et al. 2017; Tavares et al. 2019). According to Gall and Thompson (2015) entanglement and ingestion of plastic are the most frequent ways in which megafauna interact with debris and the frequency of reported encounters is increasing. 17% of species reported to interact with plastic are classified as near threatened, vulnerable, endangered or critically endangered on the IUCN Red List. Crucially, marine plastic could be contributing to population declines. 78.9% of marine mammal species are reported to have ingested or become entangled in plastic; this includes cetaceans, many of which are already under threat from multiple anthropogenic activities (Poeta et al. 2017).

Plastic can impact cetacean populations in a diversity of lethal and sub-lethal ways. Entanglement can cause drowning, lacerations, amputations, infections and altered behaviour such as decreased ability to avoid predators and obtain food, prolonged illness and death (Laist 1987, 1997). Marine debris has been found in sperm whales since the early twentieth century, when fishing hooks were found in stranded individuals in Shetland, Scotland (Turner 1904). de Stephanis et al. (2013) reported a stranded sperm whale in Granada, Spain, which had a large mass of compacted plastics in its stomach. Between January and February 2016, 30 sperm whales also stranded along the coast of the North Sea. Nine of these whales had marine debris in their gastro-intestinal tract, with up to 25 kg of debris collected from a single individual (Unger et al. 2016). A study of North Atlantic right whales by van der Hoop et al. (2016), demonstrated how entanglement in fishing gear increases the energy requirements of an entangled whale by up to 102%. This substantial energetic cost has detrimental effects, possibly causing severe emaciation and mortality. Abreo et al. (2016) reported the necropsy of a rare Deraniyagala’s beaked whale (Mesoplodon hotaula) which had ingested a 133 cm polypropylene rope, leading to fatal blockage of the gastrointestinal tract. Plastic can remain in an animal’s stomach for long periods of time, and can consequently cause satiation, ulcerations and lacerations, resulting in infections, internal bleeding and consequently prolonged illness and suffering (Day et al. 1985). Plastics can also be a potential source for toxic chemicals when ingested (Ryan 1987).

Southeast Asia is a hotspot for cetaceans, but species distributions, threats and population status are not well characterised due to a lack of funding and infrastructure in many countries (SEAMAM III 2015). Southeast Asia also has an extensive and difficult to survey coastline extending over 100,000 km and Indonesia and the Philippines alone consist of 24,000 islands (Bryant et al. 1998).

In addition to a high diversity of marine megafauna in Southeast Asia, there are also several freshwater and estuarine species. For example, both Indo-Pacific humpback dolphin (Sousa chinensis) (Vulnerable) and Irrawaddy dolphins (Orcaella brevirostris) (Endangered) inhabit freshwater and estuarine ecosystems and face numerous threats that are implicated in their decline (Minton et al. 2017; Jefferson et al. 2017). These estuarine species often exist in fragmented and isolated populations with river pollution (both chemical and litter) causing significant conservation concern (Kreb et al. 2010). There is, therefore, an urgent need for more conservation-based research into the ecology, distribution and threats of plastic pollution on Southeast Asian cetaceans, encompassing estuarine, coastal and offshore species, to assess impacts at both the individual- and population- level (Abreo et al. 2019).

There is a lack of literature relating to cetaceans and litter, especially considering Southeast Asia’s large contribution of marine plastic pollution (Jambeck et al. 2015). According to the Web of Science, of the ASEAN member states, the Philippines was the subject of the most English language studies published between 2009 and 2019 (n = 4), followed by Thailand (n = 2). Singapore, Cambodia and Indonesia all had one relevant study; and the remaining member states none.

These studies include Obusan et al. (2016) who analysed strandings from 1998 to 2013 in the Philippines, with notes on the impact of fisheries interactions, and vulnerable cetacean species. The study reports that 33% of the strandings were confirmed to be related to human interaction. Aragones et al. (2010) discussed the causes of cetacean strandings in the Philippines but did not specifically focus on marine debris. Other studies focus on individual species; for example, Baird and Beasley (2005) revealed how bycatch is a threat to the Irrawaddy dolphin (Orcaella brevirostris) population in the Mekong River. Overall however, there are no standardised methods for assessing the extent of the marine litter problem (Nelms et al. 2015), and therefore, no comparison could be made from literature between each ASEAN member state.

To address a lack of data, both on plastics and cetaceans in Southeast Asia, we used data from social media posts. Social media is an efficient tool for this purpose due to its accessibility and global reach (Bik and Goldstein 2013), Facebook being the most widely used social media platform with 2.6 billion users at the start of 2020 (www.​statista.​com). Previous studies show the utility of social media for such research. For example, Sidlauskas et al. (2011) highlighted the utility of such platforms for successfully identifying thousands of fish specimens in South America. Citizen science in combination with social media has also provided valuable data on the interactions between roe deer and Northern chamois in the Italian Alps (Mori et al. 2018). Such studies indicate the efficacy of social media derived data that span a large temporal and spatial scale.

This study uses data from social media, specifically Facebook, to identify cetacean stranding events associated with marine litter across Southeast Asia and provides insights into cetacean distributions and foraging behaviour in regions where their biology is not well understood.

A total of 163 stranding events were posted on Facebook from 2009 to 2019 in Southeast Asia, which comprised the stranding of 221 individuals (including four mass stranding events). 25% of strandings (n = 41) showed signs of litter interaction (all data in Supplementary Materials). According to the Facebook data, of the estimated 47 cetacean species in Southeast Asian waters (SEAMAM III 2015), 15 species were recorded as stranding for reasons related to plastic (common and Indo-Pacific bottlenose dolphins are counted as one species), therefore, at least 32% of cetacean species in Southeast Asia are interacting with marine litter. These stranding events involved two mysticetes: a Bryde’s whale and an unidentified baleen whale; the remainder were all odontocetes. Seven species were recorded more than once. Species which stranded the most frequently in relation to litter were the Irrawaddy dolphin (n = 6), and the pygmy sperm whale (Kogia breviceps) (n = 5) (Table 1).

Of the total stranding events, 25.2% were related to marine litter, either ingestion (56.1%) or entanglement (41.5%) (Table 1). There was additionally a single case best categorised as entrapment (a Bryde’s whale trapped in a fish corral in the Philippines).

Ingestion in deep divers is much higher in comparison to species that forage closer to the surface, which appear more likely to become entangled (Fig. 1a). 94% of the plastic-related strandings involving deep diving species were due to ingestion (including sperm whales, pygmy and dwarf sperm whales, pilot whales and beaked whales), whereas 67% of strandings of species that forage nearer to the surface resulted from entanglement (Fig. 1b).

Out of the ten countries, the Philippines had the highest frequency of strandings (n = 102), with 28.4% (n = 29) in relation to litter. Litter interactions in the Philippines were the most frequent in the Davao region (Region XI) (n = 10). Indonesia had the most strandings following the Philippines (n = 20), of which four were litter related. The Philippines also had the most species recorded to interact with litter (n = 14), followed by Indonesia and Malaysia (n = 4). Five countries (Singapore, Myanmar, Vietnam, Brunei and Laos), however, had no Facebook posts on strandings related to litter and Brunei and Laos had no posted strandings at all. Singapore, Brunei and Laos have the three smallest coastlines (Laos being entirely landlocked) and the fewest numbers of Facebook users compared to the other member states. Our study also found Cambodia to have reported three litter-related strandings on Facebook (Table 2; Fig. 2).

The majority of stranding events were not necropsied, with only 22% (n = 36) reported as being necropsied by a trained professional. 78% of necropsied individuals had interacted with litter. Malaysia had the highest proportion of strandings necropsied (40%), followed by Cambodia (33%). The Philippines and Thailand, each had 25% necropsied. Facebook posts in Singapore, Vietnam and Myanmar all had no evidence of necropsies, and so the frequency of ingestion could not be ascertained (Table 2, Fig. 3). The most frequent litter-types found ingested in stranded individuals was plastic bags (23%), followed by packaging, which included food wrappers and containers (Table 3).

In this study, the most frequent species to experience litter-related strandings was the Irrawaddy dolphin which is found in coastal, lacustrine and riverine waters throughout Asia (Stacey and Arnold 1999). Each litter-related stranding involved entanglement in fishing gear. In Southeast Asia subsistence and commercial fisheries are extensive, and accidental bycatch in gillnets remains a significant threat to river dolphin populations (Lewison et al. 2004). The riverine populations include the Mekong River (Cambodia, Lao PDR and Vietnam), the Mahakam River (Indonesia) and the Ayeyarwady River (Myanmar). Irrawaddy dolphins as a species are now classified as Endangered by the IUCN, but freshwater populations that are isolated from the marine environment, face greater threat than their marine counterparts. Such freshwater populations, together with those in the Malampaya Sound in the Philippines, are considered Critically Endangered (Minton et al. 2017).

The Mekong River Irrawaddy dolphins are genetically distinct from the other riverine populations, possibly representing a subspecies (Beasley et al. 2005). Preserving the existing genetic diversity is a high priority to ensure long-term survival of the species (Krützen et al. 2018). As a result, the establishment of protected areas with no gillnet fishing have been recently implemented for the conservation of the dolphin in Cambodia. These areas are enforced by the Mekong River Guard Program. The program is thought to be a significant factor in the recent increase in calf survival but the authorities need to ensure that illegal fishermen are successfully prosecuted to achieve the goal of zero dolphin mortality caused by fishing (Limsong et al. 2017).

Of the six Irrawaddy dolphin litter-related strandings recorded from the Facebook search, two were in the Malampaya Sound (Philippines), one by the Mahakam River (Indonesia), two by the Mekong River (Cambodia) and one by the Batang Matu River, in Sarawak in Malaysia. All strandings of this species in the Philippines were recorded as a result of entanglement in discarded fishing nets, and all other posts appeared to be bycatch according to the text and images in the post. These results further emphasise that freshwater populations of Irrawaddy dolphins are more vulnerable than those in marine areas, and that entanglement in gill nets is still a substantial threat. The Sarawak stranding is of particular interest because the presence of Irrawaddy dolphins in this location is less well documented, this highlights a key knowledge gap in the species’ distribution which needs to be addressed to establish a better system for assessing and mitigating bycatch. River mouths are known to accumulate plastics, particularly during periods of low freshwater discharge (van Emmerik et al. 2020), making Irrawaddy dolphins particularly vulnerable at certain periods of the year. Whilst this study has aided understanding of the Irrawaddy dolphin’s spatial distribution, there has been no range-wide survey and further assessments of population dynamics are required for effective long-term management.