Quantifying the Effects of Diver Interactions on Manta Ray Behavior at Their Aggregation Sites

Abstract

Manta rays (Mobula birostris, Mobula. cf. birostris, and Mobula alfredi), the largest mobulid rays, are subjected to exploitation and overfishing in certain parts of the world. Tourism has been supported as a sustainable alternative for the conservation of the species, and a potential source of economic spillover to local populations. Nevertheless, the effects of tourism over these highly social animals remains unknown. Manta rays aggregate at three sites in Mexico: Oceanic manta rays (M. birostris) in The Revillagigedo Archipelago and Banderas Bay in the Pacific. Caribbean manta rays (M. cf. birostris) around Isla Contoy National Park in the Caribbean. We analyzed the behavior of manta rays using video data collected by local researchers and tourism operators to determine how diver behaviors and techniques (SCUBA and free diving) affect them. Diver activities were grouped into passive and active categories. We described 16 behaviors and grouped them into four behavioral states: Directional, erratic, attraction and evasion to divers. We modeled the sequence of behaviors exhibited by manta rays via first order Markov chains. Our models accounted for passive and active diver behavior when modeling the changes in manta behavior. Manta rays in Banderas Bay and Revillagigedo displayed a higher frequency of erratic behaviors than at Isla Contoy, while Banderas Bay manta rays transitioned to evasion behaviors more often. Manta rays responded similarly in both sites to active divers. At freediving sites, manta rays from Isla Contoy displayed evasion less frequently than at Banderas Bay. Changes in manta ray behavior were similar for both sites, but mantas in Banderas Bay transitioned to evasion more with active divers. The increased food availability for Isla Contoy manta rays could be the reason for the reduced response toward divers in this site. The existence of additional stressors such as both traffic in Banderas Bay could be causing the mantas in this site to respond more frequently to active divers. This study, the first of its kind in oceanic and Caribbean manta rays, highlights that regulations and the use of best practices are vital for achieving longer and less disturbing encounters for both manta rays and divers.

Residency, movement patterns, behavior and demographics of reef manta rays in Komodo National Park

“…Further, tourism boats dropping off and picking up divers commonly drive over the shallow reef housing cleaning stations creating noise pollution, which startles cleaning rays (E. Germanov, 2017, personal observation). Excessive boats and divers on the site could substantially reduce the quality or length of cleaning station visits by manta rays, similar to the disturbance of feeding rays by swimmers elsewhere ( Gómez-García et al, 2021 ; Murray et al, 2020 ; Venables et al, 2016 ). Cleaning provides manta rays with a vital health service i.e ., removing parasites and facilitating wound healing, and its disruption could affect individual fitness ( O’Shea, Kingsford & Seymour, 2010 ).…”

Manta and devil ray aggregations: conservation challenges and developments in the field

“…In a recent study, avoidance responses by M. alfredi at Hanifaru were reported in 37% of the observations, and the animals' natural behavior was stopped or changed during in-water interactions with humans (Murray et al, 2020). In Mexico, M. birostris at aggregation sites showed higher probabilities of evasive behavior when interacting with divers actively chasing individuals (Goḿez-Garcıá et al, 2021). While several studies have described anthropogenic disturbances for manta rays at aggregation sites (Venables, 2013;Germanov et al, 2019;Murray et al, 2020;Goḿez-Garcıá et al, 2021), and addressed potentially problematic human-manta interactions by developing science-based best practices guidelines or codes of conduct (e.g.…”

“…Predictable aggregations of mobulids at specific locations offer opportunities to develop non-consumptive uses such as ecotourism focused on observing and swimming with mobulids. Tourist activities with mobulids at aggregation sites have been reported for several species worldwide: M. alfredi in Australia, Indonesia, and Maldives (Venables, 2013;Germanov et al, 2019;Murray et al, 2020), M. birostris in Mexico and Ecuador (Kumli and Rubin, 2010;Burgess, 2017;Goḿez-Garcıá et al, 2021;Harty et al, 2022), M. tarapacana in the Azores (Sobral, 2013;Solleliet-Ferreira et al, 2020), and M. munkiana in the Gulf of California (Palacios et al, 2021). Manta and devil ray tourism not associated with aggregation sites is also widespread globally (O'Malley et al, 2013).…”

“…In Mexico, M. birostris at aggregation sites showed higher probabilities of evasive behavior when interacting with divers actively chasing individuals (Goḿez-Garcıá et al, 2021). While several studies have described anthropogenic disturbances for manta rays at aggregation sites (Venables, 2013;Germanov et al, 2019;Murray et al, 2020;Goḿez-Garcıá et al, 2021), and addressed potentially problematic human-manta interactions by developing science-based best practices guidelines or codes of conduct (e.g. How to Swim with Manta Rays; swimwithmantas.…”

“…As a result, all mobulid species are listed as Endangered or Vulnerable on the IUCN's Red List of Threatened Species (IUCN, 2020). Furthermore, mobulid aggregations in coastal areas can lead to exposure to boat collisions (Germanov et al, 2019;Pate and Marshall, 2020;Strike et al, 2022), habitat degradation (Stewart et al, 2018a) and unregulated tourism impacts (Venables, 2013;Murray et al, 2020;Goḿez-Garcıá et al, 2021). The identification of aggregation sites for some species has led to the creation of Marine Protected Areas (MPAs) (e.g., UNESECO World Heritage Sites Revillagigedo Archipelago in Mexico, and Hanifaru Bay MPA in Maldives) and the establishment of management measures, such as best practices to reduce the mortality of mobulids caught incidentally by tuna purse seiners, or codes of conducts to ensure responsible tourism practices (Poisson et al, 2012;Lezama-Ochoa et al, 2019b;Murray et al, 2020;Cronin et al, 2022).…”