DOI: 10.5061/dryad.8cz8w9gxd
title: Data for: Manta rays in the Maldives foraging either in groups or solo

description: Flexibility in animal foraging strategies can increase overall feeding
 efficiency. For example, group foraging can increase the efficiency of
 resource exploitation; conversely, solo foraging can reduce intraspecific
 competition, particularly at low resource densities. The cost-benefit
 trade-off of such flexibility is likely to differ within and among
 individuals. Reef manta rays (Mobula alfredi) are large filter-feeding
 elasmobranchs that often aggregate to feed on ephemeral upwellings of
 zooplankton. Over three years in the Maldives, we free-dived to film 3106
 foraging events involving 343 individually identifiable M. alfredi.
 Individuals fed either solo or in groups with a clear leader plus between
 one and eight followers. M. alfredi were significantly more likely to
 forage in groups than solo at high zooplankton levels, and at certain
 locations. Both biotic and abiotic factors contributed to variation in
 group foraging. Within aggregations, individuals foraged in larger groups
 when more food was available, and when the overall aggregation was
 relatively small suggesting that foraging in large groups was more
 beneficial when food was abundant, and/or the costs of intraspecific
 competition were outweighed by the efficiency resulting from group
 foraging strategies. Females, the larger sex, were more likely to lead
 foraging groups than males. The high within-individual variance (over
 55%), suggested individuals were unpredictable across all foraging
 behaviours, thus individual M. alfredi cannot be classified into foraging
 types or specialists. Instead, each individual was capable of considerable
 behavioural flexibility, as predicted for a species reliant on spatially
 and temporally ephemeral resources.
description: Collected in the field via video clips. Briefly:
 We collected data on manta ray feeding behaviour at different
 times of day as part of the Manta Trust’s Maldives Manta Conservation
 Programme (https://www.mantatrust.org/maldives) during the Southwest
 Monsoon (May through November) when the highest numbers of mantas are
 present. Data collection lasted for 160 days in 2014, 156 days in 2015,
 and 155 days in 2016. We identified five sites on the eastern side of Baa
 Atoll that served as the main monitoring spots: Dhigu Thila, Hanifaru Bay,
 Hurai Faru, Reethi Falhu and Veyofushi Falhu. Due to the restriction on
 SCUBA diving at the main study site, Hanifaru Bay, all foraging data was
 collected by free diving. When we spotted foraging events, we free-dived
 beneath the animals to video their behaviour and record the unique
 identification spots on the ventral surface (Marshall & Pierce
 2012), taking care not to impede or alter this behaviour. If, on entering
 the water, we observed more than one <em>M. alfredi </em>in
 the immediate vicinity, we dived to be in position before the first animal
 in the group swam overhead. If the animal was feeding, we filmed
 continuously until feeding stopped, until the last member of the group
 passed from sight, or we ran out of breath. We terminated filming once
 reaching the surface, and a clear view of the ventral markings was lost.
 Clips lasted between 30 and 180 seconds and were collected between depths
 of five and 16 metres. As feeding events could last up to a few hours,
 video clips of individual feeding groups were recorded on a consecutive
 basis as they arose until the feeding event finished or until the weather
 or daylight deteriorated. We filmed using a GoPro Hero 3, or a Canon
 PowerShot S110 compact camera. It was not possible to record data blind
 because our study involved focal animals in the field.
description: # Data for: Manta rays in the Maldives foraging either in groups or solo
 [https://doi.org/10.5061/dryad.8cz8w9gxd](https://doi.org/10.5061/dryad.8cz8w9gxd) ## Description of the data and file structure The data file is an Excel spreadsheet containing the raw data collected in the field and extracted from video clips. Empty cells indicate that the data are not available - i.e., they were not collected in the field or could not be seen on the videos. Variable definitions: * npid and id: unique ID of the animal * day: Julian day * year and nyear: year of observation * site: Dhigu Thila, 1 = Hanifaru Bay, 2 = Hurai Faru, 3 = Reethi Falhu and Veyofushi Falhu * clips: video clip duration (s) * sex: 1 = Female, 2 = male * size: score of relative size * maturity: 1=juvenile, 2 = adult * group_ID: unique identifier code of group * group_size: number of mantas in observed group * position: position in group - 1= 1st etc * seconds: duration of observation (s) * time: time of day of recording * time_ht: time to high tide (minutes) * high_tide: time of high tide * no_mantas: number of mantas in group * manta_trans: number of mantas in group transformed * leader: the focal animal leading the foraging group? 0 = no, 1 = yes * follower: the focal animal a follower in the foraging group? 0 = no, 1 = yes * no_people: number of humans in water at aggregation * people_trans: number of people transformed * plankton: plankton score: 1 = low, 2 = medium, 3 = high * current: current strength was gauged using a scale from “no current” (0) to “strong” (3): (no current (0) – researcher able to hold position without finning; weak (1) – researcher able to hold position with little effort; medium (2) – researcher able to hold position with strong finning; Strong (3) – researcher unable to hold position (Manta Trust, unpublished data)). * clip: unique clip ID * injury: did the manta have an injury 0 = no, 1 = yes * shark_bite: If yes, did the injury appear to be a shark bite? 0 = no, 1 = yes * anthropogenic: did the injury appear to be from an anthropogenic source? 0 = no, 1 = yes * pregnant: 0 = not pregnant, 1 = pregnant ## Sharing/Access information NA ## Code/Software We conducted the analysis using the R 3.0.0 Statistics Package (R Core Team, 2020), aiming to answer these specific study questions. Full models are outlined in Table 1 in the main paper. All code for reproducing the statistical analyses and results is available on GitHub: [https://github.com/rroyaute/mantarays-iiv-analysis](https://github.com/rroyaute/mantarays-iiv-analysis)