Abstract
Though extremely valuable to the local marine tourism industry, there is a dearth of published information on the ecology and population dynamics of reef manta rays (Mobula alfredi) in Raja Ampat, West Papua, Indonesia. Knowledge of the movement ecology in particular of this large and scattered population is urgently needed to better manage the rapidly expanding manta-focused tourism. Here we report the results of an initial passive acoustic telemetry study designed to provide local managers with the first detailed knowledge of the site use and movement patterns of reef mantas in northern Raja Ampat. A total of 39 reef mantas were tagged with Vemco V16 acoustic transmitters over a 15-month period between 27 November 2013 and 22 February 2015. To monitor their movements, VR2W acoustic receivers were deployed at eight sites corresponding to known manta cleaning and feeding aggregation sites, with receivers downloaded every six months over a two-year initial monitoring period. The duration between tag deployments and last date of detections at sites ranged from 1 to 682 days (mean ± SE = 237 ± 27). The cumulative number of days of manta detections at receiver sites by individual mantas ranged from 1 to 188 days (mean ± SE = 42 ± 7). Manta Ridge was the most popular site with 565 days of detections. The tagged mantas demonstrated strong site fidelity to the observed aggregation sites, but also exhibited seasonal movements within an approximately 150 km long corridor between sites in the Dampier Strait and the northwest of Waigeo Island. Data analysed from a nearby array of six VR2W receivers in southern Raja Ampat (approximately 180 km to the south of the study area) confirmed that none of the tagged mantas were detected in this array, providing further evidence of strong site fidelity and limited movements within the Raja Ampat Archipelago. More than 96% of detections occurred during the daytime. The number of detections reached a peak around noon at Yefnabi Kecil and Eagle Rock and slightly earlier at Manta Ridge. These findings have been shared with the Raja Ampat Marine Protected Area Management Authority and are now being used in the formulation of a management plan for this vulnerable and economically important species to ensure the long-term health of Raja Ampat’s reef mantas and the sustainability of manta tourism in the region.
Highlights
Long considered a junior synonym of the oceanic manta ray Mobula birostris (Walbaum, 1792), the reef manta ray Mobula alfredi (Krefft, 1868) was shown by Marshall et al (2009) to represent a valid species based upon consistent morphological, meristic, colour pattern and behavioural differences
The 45 000 km2 Raja Ampat Archipelago in West Papua, Indonesia (Fig. 1) is home to a large population of reef manta rays (Mangubhai et al, 2012) and is one of only a handful of sites worldwide where both species of manta ray are regularly encountered (Kashiwagi, 2014), including at a number of cleaning stations utilised by both species simultaneously (Authors’ data)
Reef manta tagging A total of 39 mantas were tagged in three different periods, consisting of 14 mantas between November and December 2013, 13 mantas between April and May 2014, and 12 mantas in February 2015
Summary
Long considered a junior synonym of the oceanic manta ray Mobula birostris (Walbaum, 1792), the reef manta ray Mobula alfredi (Krefft, 1868) was shown by Marshall et al (2009) to represent a valid species based upon consistent morphological, meristic, colour pattern and behavioural differences. Mangubhai et al (2012) report known aggregations of M. alfredi from four of Raja Ampat’s eight marine protected areas (MPAs), while Stewart et al (2016) describe the movements of ten M. birostris individuals as revealed by satellite tagging. This relative dearth of information impedes effective manta conservation in the region, as understanding the movement patterns and habitat preferences of potentially migratory elasmobranch species is widely considered critical for determining effective management strategies (Graham et al, 2012)
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