Regional Movements of Reef Manta Rays (Mobula Alfredi) in Seychelles Waters
Total Page：16
File Type：pdf, Size：1020Kb
fmars-07-00558 July 10, 2020 Time: 16:32 # 1 ORIGINAL RESEARCH published: 10 July 2020 doi: 10.3389/fmars.2020.00558 Regional Movements of Reef Manta Rays (Mobula alfredi) in Seychelles Waters Lauren R. Peel1,2,3,4*, Guy M. W. Stevens3, Ryan Daly4,5,6, Clare A. Keating Daly4, Shaun P. Collin1,7, Josep Nogués8 and Mark G. Meekan2 1 School of Biological Sciences, Oceans Institute and Oceans Graduate School, The University of Western Australia, Crawley, WA, Australia, 2 The Australian Institute of Marine Science, Crawley, WA, Australia, 3 The Manta Trust, Corscombe, United Kingdom, 4 Save Our Seas Foundation – D’Arros Research Centre, Geneva, Switzerland, 5 South African Institute for Aquatic Biodiversity, Grahamstown, South Africa, 6 Oceanographic Research Institute, Durban, South Africa, 7 School of Life Sciences, College of Science, Health and Engineering, La Trobe University, Bundoora, VIC, Australia, 8 Island Conservation Society, Pointe Larue, Seychelles The decline in numbers of reef manta rays (Mobula alfredi) throughout their range has highlighted the need for improved information on their spatial ecology in order to design effective conservation strategies for vulnerable populations. To understand their patterns of movement in Seychelles, we used three techniques—archival pop-up satellite tags, acoustic tags, and photo-identification—and focussed on the aggregation at D’Arros Island and St. Joseph Atoll within the Amirantes Group. M. alfredi were photographed within six of the seven Island Groups of Seychelles, with 64% of individuals being Edited by: resighted at least once between July 2006 and December 2019 over timeframes of Lars Bejder, 1–3,462 days (9.5 years; median = 1,018 days). Only three individuals from D’Arros University of Hawai’i at Mânoa, United States Island were resighted at a second aggregation site located more than 200 km away at Reviewed by: St. François Atoll during photo-identification surveys. Satellite-tracked M. alfredi (n = 5 Nuno Queiroz, tracks; maximum 180 days) remained within the boundary of the Seychelles Exclusive University of Porto, Portugal Philip D. Doherty, Economic Zone, where they spent the majority of their time (87%) in the upper 50 m University of Exeter, United Kingdom of the water column in close proximity to the Amirantes Bank. The inclusion of acoustic *Correspondence: tagging data in the models of estimated satellite-track paths significantly reduced the Lauren R. Peel errors associated with the geolocation positions derived from archived light level data. [email protected] The insights gained into the patterns of horizontal and vertical movements of M. alfredi Specialty section: using this multi-technique approach highlight the significance of D’Arros Island and St. This article was submitted to Joseph Atoll, and the wider Amirantes Group, to M. alfredi in Seychelles, and will benefit Marine Megafauna, a section of the journal future conservation efforts for this species within Seychelles and the broader Western Frontiers in Marine Science Indian Ocean. Received: 07 February 2020 Accepted: 17 June 2020 Keywords: spatial ecology, acoustic telemetry, satellite telemetry, geolocation, Western Indian Ocean, Published: 10 July 2020 conservation Citation: Peel LR, Stevens GMW, Daly R, INTRODUCTION Keating Daly CA, Collin SP, Nogués J and Meekan MG (2020) Regional Movements of Reef Manta Rays Reef manta rays (Mobula alfredi; Marshall et al., 2009; White et al., 2017) are large, zooplanktivorous (Mobula alfredi) in Seychelles Waters. elasmobranchs with a circumtropical distribution (Couturier et al., 2012; Stewart et al., 2018). Front. Mar. Sci. 7:558. Aggregations of these mobulid rays (Family Mobulidae; Notarbartolo di Sciara, 1987; Couturier doi: 10.3389/fmars.2020.00558 et al., 2012; White et al., 2017) occur at numerous locations around the world, however, they are Frontiers in Marine Science| www.frontiersin.org 1 July 2020| Volume 7| Article 558 fmars-07-00558 July 10, 2020 Time: 16:32 # 2 Peel et al. Regional Movements of Seychelles Mantas being increasingly exploited for their gill plates for use in the M. alfredi populations occur (Kashiwagi et al., 2011; Couturier Asian medicinal trade (White et al., 2006; O’Malley et al., et al., 2012). 2017). This fishing pressure, coupled with the impacts of Acoustic telemetry offers an alternative to archival pop-up other anthropogenic threats, including boat strike, accidental satellite tagging as a means of describing movement patterns entanglement, and by-catch, has resulted in global declines of of M. alfredi (Clark, 2010; Braun et al., 2015; Couturier et al., M. alfredi populations (Couturier et al., 2012; Croll et al., 2016; 2018; Setyawan et al., 2018; Andrzejaczek et al., 2020). Acoustic Stewart et al., 2018). In the last decade, positive conservation tags transmit a uniquely coded signal that is passively detected measures for M. alfredi have been taken at the international level whenever the tagged individual moves within the detection (Croll et al., 2016; Marshall et al., 2018). However, at local (i.e., radius of receivers deployed at the study site (Heupel et al., 2006). regional and national) scales, where intensive fishing practices Although many more animals can be monitored using acoustic can cause rapid and persistent declines in populations (Dewar, tags due to their lower cost (relative to satellite tags), acoustic 2002; Rohner et al., 2017; Marshall et al., 2018), management tracking is restricted to the spatial extent of the receiver array strategies are less defined and can be difficult to establish. Local that is deployed to detect tagged individuals (Stewart et al., 2018). management is further complicated by the ability of M. alfredi Additionally, receivers must be recovered and downloaded to to travel large distances away from the aggregation sites at obtain detection data (Heupel et al., 2006). which they are commonly sighted (50–1,150 km; Couturier In contrast to the cost and logistics involved with satellite et al., 2011; Deakos et al., 2011; Jaine et al., 2014; Armstrong and acoustic tagging, photo-identification offers a simple means et al., 2019). Such movements highlight the difficulty associated to examine site-fidelity and movement patterns of M. alfredi with quantifying the magnitude and impact of anthropogenic (Marshall and Pierce, 2012). Photographs of the unique and pressures on M. alfredi populations throughout their range. permanent ventral markings on individual M. alfredi can be An understanding of the patterns of movement and habitat used to examine levels of site fidelity and residency exhibited by use of M. alfredi not only at aggregation areas, but also away cohorts of a population, and to assess the frequency at which from these sites, is therefore critical to the design of effective individuals travel between aggregation sites (Kitchen-Wheeler, conservation measures aimed at protecting their populations 2010; Deakos et al., 2011; Marshall et al., 2011; Marshall and from unsustainable exploitation at local scales. Pierce, 2012). This technique is, however, usually biased to Satellite tracking represents an effective means to monitor the areas where M. alfredi are already known to aggregate, and movement patterns of megafauna (Hays et al., 2016; Sequeira information on the fine-scale (hours to days) movements of et al., 2018) and is providing researchers insights into both individuals between locations is often absent (Deakos et al., the large (100s to 1000s of km) and fine (0.1s to 1s of km) 2011). Additionally, it can be logistically difficult to gain access scale movement patterns of M. alfredi (Braun et al., 2014, to and continuously survey aggregation sites, particularly in 2015; Jaine et al., 2014; Kessel et al., 2017; Andrzejaczek et al., remote locations. These challenges can result in seasonally biased 2020). Datasets retrieved from archival pop-up satellite tags datasets that may not be completely representative of the annual can be used to visualize the horizontal extent of movement of movement patterns of the population. individuals throughout their home range, and can also reveal Some of the shortcomings of satellite and acoustic tagging, and the drivers of horizontal and vertical movements through the photo-identification techniques, may be overcome by combining water column (Canese et al., 2011; Jaine et al., 2014; Kessel these approaches (Meyer et al., 2010; Kneebone et al., 2014; et al., 2017; Andrzejaczek et al., 2018; Lassauce et al., 2020). In Vianna et al., 2014; Braun et al., 2015). Detections of acoustic contrast to satellite tags that communicate solely with satellites tags within receiver arrays, individually or combined with to report the locations tagged individuals (e.g., SPOT tags), pop- sighting records of tagged individuals at aggregation sites, can up archival tags are also programmed to log light, temperature, be used to reduce the uncertainty surrounding location estimates and depth data for a predetermined period of time. Upon derived from geolocation analyses (Werry et al., 2014; Cochran release from the individual, archived data are transmitted from et al., 2019). This combined approach improves the accuracy the tag in segments via satellite, or downloaded in full when of individual tracks provided by archival pop-up tags. In turn, the tag is retrieved. Geolocation processes are then used to tracking data can provide a better picture of both large-scale estimate the most-likely track path of tagged individuals based movement and home range of individuals, allowing