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

Abstract

Background The reef manta ray (Mobula alfredi) is a globally threatened species and an iconic tourist attraction for visitors to Indonesia’s Komodo National Park (NP). In 2013, manta ray fishing was banned in Komodo NP and its surroundings, preceding the nationwide manta ray protection in 2014. Over a decade ago, a previous acoustic telemetry study demonstrated that reef manta rays had high fidelity to sites within the park, while more recent photo-identification data indicated that some individuals move up to 450 km elsewhere. Characterization of manta ray demographics, behavior, and a focused assessment on site use of popular tourism locations within the park is vital to assist the Komodo NP Management Authority formulate appropriate manta ray conservation and management policies. Methods This study uses a long-term library (MantaMatcher.org) of photo-identification data collected by researchers and citizen scientists to investigate manta ray demographics and habitat use within the park at four sites frequented by tour operators: Cauldron, Karang Makassar, Mawan, and Manta Alley. Residency and movements of manta rays were investigated with maximum likelihood analyses and Markov movement models. Results A total of 1,085 individual manta rays were identified from photographs dating from 2013 to 2018. In general, individual manta rays displayed a higher affinity to specific sites than others. The highest re-sighting probabilities came from the remote southern site, Manta Alley. Karang Makassar and Mawan are only ~5 km apart; however, manta rays displayed distinct site affinities. Exchange of individuals between Manta Alley and the two central sites (~35.5 km apart) occurred, particularly seasonally. More manta rays were recorded traveling from the south to the central area than vice versa. Female manta rays were more mobile than males. Similar demographic groups used Karang Makassar, Mawan, and Manta Alley for foraging, cleaning, cruising, or courtship activities. Conversely, a higher proportion of immature manta rays used the northern site, Cauldron, where foraging was commonly observed. Fishing gear-related injuries were noted on 56 individuals (~5%), and predatory injuries were present on 32 individuals (~3%). Tourism within the park increased from 2014 to 2017, with 34% more dive boats per survey at Karang Makassar and Mawan. Discussion The Komodo NP contains several distinct critical habitats for manta rays that encompass all demographics and accommodate seasonal manta ray movements. While the present study has not examined population trends, it does provide foundational data for such work. Continued research into manta ray abundance, long-range movements, and identifying and protecting other critical aggregation areas within the region is integral to securing the species’ recovery. We provide management recommendations to limit undue pressure on manta rays and their critical habitats from tourism.

Population estimates of photo-identified individuals using a modified POPAN model reveal that Raja Ampat’s reef manta rays are thriving

“…Despite several studies reporting biennial or longer reproductive periodicities (Marshall and Bennett, 2010;Deakos et al, 2011;Stevens, 2016), a total of 16 female M. alfredi in Raja Ampat were recorded with annual reproductive periodicity, including one exceptional individual which had four consecutive-year pregnancies and a total of five pregnancies confirmed in seven years. Setyawan et al (2020;2022b) reported four M. alfredi nurseries in Raja Ampat, and 65 young-of-the-year (YoY) were identified between 2011 and 2019, a number that surpasses other published studies (Marshall and Bennett, 2010;Couturier et al, 2014;Stevens, 2016;Germanov et al, 2019;Germanov et al, 2022). These findings all support the suggestions of our models that M. alfredi (sub)populations are growing in both Raja Ampat MPAs studied here, with high fecundity and per capita recruitment rates.…”

Comparative population genomics of manta rays has global implications for management

“…These results are in line with recent studies demonstrating population differentiation between Western Australia and Mozambique (Venables et al, 2021) and between Eastern Australia and New Caledonia (Lassauce et al, 2022), together highlighting how large ocean basins form significant barriers to dispersal in coastal elasmobranchs (Hirschfeld et al, 2021). High site-fidelity has been widely reported in M. alfredi based on tagging and mark-recapture studies (Braun et al, 2015; Deakos et al, 2011; Germanov et al, 2022; Jaine et al, 2014; Knochel, Hussey, et al, 2022; Peel et al, 2019; Setyawan et al, 2018). However, the degree of residency has been shown to vary, with movements rarely exceeding a few hundred kilometres in some locations (Braun et al, 2015; Deakos et al, 2011; Kessel et al, 2017; Knochel, Hussey, et al, 2022; Setyawan et al, 2018) yet reaching over 1,000 km in others (Armstrong et al, 2019; Germanov & Marshall, 2014).…”

“…They comprise two described species estimated to have diverged less than 0.5 Mya as a result of distinct habitat preferences (Kashiwagi et al, 2012). The reef manta ray (Mobula alfredi) frequents near-shore tropical reef environments, such as coral atolls and barrier reefs (Kashiwagi et al 2011), with a high degree of residency (Deakos et al 2011;Jaine et al 2014;Braun et al 2015;Setyawan et al 2018;Peel et al 2019;Knochel et al 2022b;Germanov et al 2022). In contrast, while the oceanic manta ray (Mobula birostris) also inhabits near-shore environments, it is often found ranging into sub-tropical habitats along continental coastlines and at oceanic islands, usually adjacent to productive deep-water upwellings (Kashiwagi et al 2011;Andrzejaczek et al 2021).…”

Genomic evidence indicates small island-resident populations and sex-biased behaviors of Hawaiian reef Manta Rays

“…We reject the alternative hypothesis that the lack of exchange between island groups results from isolation by distance. The shortest distance between Maui Nui and Hawaiʻi Island is only 49 km, and linear movements up to 91 km have been documented elsewhere in Hawaiʻi [ 14 ] and more than 200 km between nearby islands in other archipelagos (Table S3 ) [ 11 , 12 , 16 , 60 , 75 , 76 ]. Along continental shelves with continuous coastlines, linear movements over 500 km are common [ 18 , 60 , 77 , 78 ].…”

“…However, these islands are only 0.2% of the area of Hawaiʻi Island (Table S3 ). Third, in contrast, regular inter-island movements up to 450 km have been recorded between relatively large islands in Indonesia that are connected by shallow shelves typically < 300 m [ 15 , 16 , 60 , 62 , 79 ]. These patterns reinforce the hypothesis that shallow channels and shelves create more continuous habitat that is crossed regularly, regardless of island size, but deep channels (> 300 m) are crossed infrequently and only when separating small islands or atolls.…”