Marine plastic abundance has increased over the past 60 years and microplastics (< 5 mm) constitute a primary component of such litter. Filter-feeding megafauna, such as the whale shark, might be particularly affected by microplastic pollution as their feeding mode requires filtration of up to thousands of cubic meters of water. In addition, the habitat range of whale sharks intersects with several recognized microplastic pollution hotspots, among which is the Coral Triangle. Direct evidence for microplastic ingestion in whale sharks however, has not yet been presented. Here we show that whale shark scat collected in the Philippines from 2012 to 2019 contained a mean of 2.8 microplastics g− 1. Contrary to our expectations, the microplastic concentration in the scat remained consistent from 2012 to 2019. Water samples from the study site in 2019 indicated that the local microplastic pollution (5.83 particles m− 3) was higher than in surface waters in other whale shark habitats, but well below other pollution hot-spots found in Southeast Asia and China (range: 100–4100 particles m− 3). With the predicted growth in plastic use, leading to increased plastic marine pollution, whale sharks are expected to become more exposed to this form of pollution. To what extent microplastic ingestion impacts the overall health status of this endangered species remains an open question.
The whale shark is the world's largest fish that forms predictable aggregations across its range, many of which support tourism industries. The largest non-captive provisioned whale shark destination globally is at Oslob, Philippines, where more than 500 000 tourists visit yearly. There, the sharks are provisioned daily, year-round, allowing the human–shark interaction in nearshore waters. We used in-water behavioural observations of whale sharks between 2015 and 2017 to understand the relationship between external stimuli and shark behaviour, whether frequency of visits at the site can act as a predictor of behaviour, and the tourist compliance to the code of conduct. Mixed effects models revealed that the number of previous visits at the site was a strong predictor of whale shark behaviour, and that provisioned sharks were less likely to exhibit avoidance. Compliance was poor, with 93% of surveys having people less than 2 m from the animal, highlighting overcrowding of whale sharks at Oslob. Given the behavioural implications to whale sharks highlighted here and the local community's reliance on the tourism industry, it is imperative to improve management strategies to increase tourist compliance and strive for sustainable tourism practices.
The world’s largest extant fish, the whale shark Rhincodon typus, is one of the most-studied species of sharks globally. The discovery of predictable aggregation sites where these animals gather seasonally or are sighted year-round – most of which are coastal and juvenile-dominated – has allowed for a rapid expansion of research on this species. The most common method for studying whale sharks at these sites is photographic identification (photo-ID). This technique allows for long-term individual-based data to be collected which can, in turn, be used to evaluate population structure, build population models, identify long-distance movements, and assess philopatry and other population dynamics. Lagged identification rate (LIR) models have fewer underlying assumptions than more traditional capture mark recapture approaches, making them more broadly applicable to marine taxa, especially far-ranging megafauna species like whale sharks. However, the increased flexibility comes at a cost. Parameter estimations based on LIR can be difficult to interpret and may not be comparable between areas with different sampling regimes. Using a unique data-set from the Philippines with ~8 years of nearly continuous survey effort, we were able to derive a metric for converting LIR residency estimates into more intuitive days-per-year units. We applied this metric to 25 different sites allowing for the first quantitatively-meaningful comparison of sightings-derived residence among the world’s whale shark aggregations. We validated these results against the only three published acoustic residence metrics (falling within the ranges established by these earlier works in all cases). The results were then used to understand residency behaviours exhibited by the sharks at each site. The adjusted residency metric is an improvement to LIR-based population modelling, already one of the most widely used tools for describing whale shark aggregations. The standardised methods presented here can serve as a valuable tool for assessing residency patterns of whale sharks, which is crucial for tailored conservation action, and can cautiously be tested in other taxa.
Cleaning interactions are essential for healthy marine ecosystem communities. This study reports the first documentation of the whale shark Rhincodon typus cleaning behaviour in the Indo-West Pacific by two wrasse species, the blue-streak cleaner wrasse Labroides dimidiatus and the moon wrasse Thalassoma lunare in Cebu, Philippines. This study documented 36 cleaning interactions with 14 individual whale sharks. The cleaning interactions appear opportunistic rather than targeted by the sharks, unlike that observed in other species of elasmobranchs. Further work should focus on understanding the drivers of these unique cleaning interactions.
Little is known about the reproductive ecology of the whale shark Rhincodon typus. On 15 March 2020, a free-swimming neonate whale shark was found in the shallow, coastal waters of Donsol, Philippines. The total length of the male shark was 60 cm, falling within the species known size-at-birth. This is the third occurrence of neonatal whale sharks reported in the area, and coupled with the occurrence of juveniles and adults, and anecdotal mating and precopulatory behaviour reported herein, the importance of the site for this endangered species is highlighted.
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