Manta and devil rays are filter-feeding elasmobranchs that are found circumglobally in tropical and subtropical waters. Although relatively understudied for most of the Twentieth century, public awareness and scientific research on these species has increased dramatically in recent years. Much of this attention has been in response to targeted fisheries, international trade in mobulid products, and a growing concern over the fate of exploited populations. Despite progress in mobulid research, major knowledge gaps still exist, hindering the development of effective management and conservation strategies. We assembled 30 leaders and emerging experts in the fields of mobulid biology, ecology, and conservation to identify pressing knowledge gaps that must be filled to facilitate improved science-based management of these vulnerable species. We highlight focal research topics in the subject areas of taxonomy and diversity, life history, reproduction and nursery areas, population trends, bycatch and fisheries, spatial dynamics and Stewart et al. Research Priorities for Mobulid Rays movements, foraging and diving, pollution and contaminants, and sub-lethal impacts. Mobulid rays remain a poorly studied group, and therefore our list of important knowledge gaps is extensive. However, we hope that this identification of high priority knowledge gaps will stimulate and focus future mobulid research.

Environmental DNA (eDNA) analysis is a rapid, non-invasive, cost-efficient biodiversity monitoring tool with enormous potential to inform aquatic conservation and management. Development is ongoing, with strong commercial interest, and new uses are continually being discovered. General applications of eDNA and guidelines for best practice in freshwater systems have been established, but habitat-specific assessments are lacking. Ponds are highly diverse, yet understudied systems that could benefit from eDNA monitoring. However, eDNA applications in ponds and methodological constraints specific to these environments remain unaddressed. Following a stakeholder workshop in 2017, researchers combined knowledge and expertise to review these applications and challenges that must be addressed for the future and consistency of eDNA monitoring in ponds. The greatest challenges for pond eDNA surveys are representative sampling, eDNA capture, and potential PCR inhibition. We provide recommendations for sampling, eDNA capture, inhibition testing, and laboratory practice, which should aid new and ongoing eDNA projects in ponds. If implemented, these recommendations will contribute towards an eventual broad standardisation of eDNA research and practice, with room to tailor workflows for optimal analysis and

Mobulid rays have a conservative life history and are caught in direct fisheries and as by-catch. Their subsequent vulnerability to overexploitation has recently been recognized, but fisheries management can be ineffective if it ignores habitat and prey preferences and other trophic interactions of the target species. Here, we assessed the feeding ecology of four mobulids (Manta birostris, Mobula tarapacana, M. japanica, M. thurstoni) in the Bohol Sea, Philippines, using stomach contents analysis of fisheries specimens landed between November and May in 2013–2015. We show that the mobulids feed heavily on euphausiid krill while they are in the area for approximately six months of the year. We found almost no trophic separation among the mobulid species, with Euphausia diomedeae as the major prey item for all species, recorded in 81 of 89 total stomachs (91%). Mobula japanica and M. thurstoni almost exclusively had this krill in their stomach, while M. tarapacana had a squid and fish, and Ma. birostris had myctophid fishes and copepods in their stomachs in addition to E. diomedeae. This krill was larger than prey for other planktivorous elasmobranchs elsewhere and contributed a mean of 61 364 kcal per stomach (±105 032 kcal s.e., range = 0–631 167 kcal). Our results show that vertically migrating mesopelagic species can be an important food resource for large filter feeders living in tropical seas with oligotrophic surface waters. Given the conservative life history of mobulid rays, the identification of common foraging grounds that overlap with fishing activity could be used to inform future fishing effort.

The characterization of diet for the giant manta ray Manta birostris has been problematic given their large-scale movement patterns and the difficulty in obtaining stomach contents from this species. The large majority of existing information is based on observational data limited to feeding events at the sea surface during daylight. Recently discovered aggregation sites for the giant manta ray off mainland Ecuador are some of the most accessible to date and provide a unique opportunity for researchers to gather much needed information on this elusive species. To assess how important surface zooplankton is to giant manta ray diet, we conducted stable isotope analysis (15N and 13C) on M. birostris muscle and surface zooplankton. Trophic position estimates placed M. birostris overall at a secondary consumer level of approximately 3.4 but there was large variation in δ15N and δ13C values among individuals. Manta birostris muscle tissue δ13C values were also not consistent with this species feeding predominantly on surface zooplankton and suggest that the majority of dietary intake is of mesopelagic origin. Given the conservative life history and fisheries pressure on large planktivores, knowledge of their trophic role and foraging strategies is essential to better understand their ecology and develop effective conservation measures.

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Mobulids have been poorly studied, but most are listed by the International Union for the Conservation of Nature as Near Threatened or of greater concern. Here we fill critical knowledge gaps surrounding reproduction for Mobula kuhlii cf. eregoodootenkee caught at 29°S -200 km south of their proposed range -off eastern Australia by bather-protection gillnets deployed for 6 mo from December 2016. M. kuhlii cf. eregoodootenkee was the second most abundant netted species (all adults: n = 63), with catches peaking in April. There was no sexual segregation, but females (disc width [DW]: 92.5 to 130.0 cm, mean ± SD 112.8 ± 7.8 cm) were significantly larger than males (99.0 to 123.0 cm, 109.4 ± 6.3 cm). Of those caught, 45 died (71% mortality), of which 20 females and 11 males were assessed for reproduction. Nine females were pre-ovulatory and non-gravid with 7 to 23 oocytes in their left ovary, while 11 had 14 to 40 ovarian oocytes and 1 embryo (DW: 7.0 to 21.2 cm) in their left uterus. The diameter of the largest ovarian follicle in gravid females was not correlated with embryo size, indicating ovulation may not occur immediately after parturition. The development of the largest embryo (DW: 21 cm) suggests parturition occurs well above this size. Males had calcified claspers and exhibited large variation in their testes weights, which might imply seasonal fluctuation in sperm production. In addition to extending the distribution of the species and increasing maximum DW to 130 cm, the data provide further evidence of the low reproductive output of M. kuhlii cf. eregoodootenkee, and a need for their effective management.

Ethanol storage and lipid and urea extraction had no effect on bluespotted maskray Neotrygon kuhlii muscle δ C values whereas urea-removal and ethanol storage increased δ N values. Results presented here show a significant δ N increase post-urea removal and provide additional support for this approach in future elasmobranch stable-isotope analysis (SIA) studies. Further experimental work on other elasmobranch species is needed to assess extraction and preservation effects on stable-isotope (SI) values.

Manta rays (Manta spp.) are among the largest elasmobranch fishes and currently comprise two recognised species, the reef manta ray Manta alfredi and the giant manta ray Manta birostris. Both Manta spp. have circumglobal distributions in tropical and temperate oceans, however, M. alfredi is more commonly encountered in coastal environments, whereas M. birostris is generally more elusive and typically sighted offshore. As such, collection of information on the feeding ecology, and the identification of drivers of habitat use for M. birostris has been difficult, particularly given the paucity of accessible and predictable locations where this species occurs. A newly discovered aggregation site at Isla de la Plata, off mainland Ecuador, hosts the largest known population of M. birostris from June to October each year, with over 2400 individuals recorded since 2009. However, the drivers for this seasonal aggregation within the Humboldt upwelling system are unknown. As aggregative behaviour of planktivorous elasmobranchs is often attributed to food availability, the aim of this study was to examine whether feeding opportunities constitute the primary driver of this sizeable aggregation of M. birostris at Isla de la Plata. We first define the inter-annual and seasonal variation in recorded numbers of M. birostris and investigate the relationship between M. birostris sightings and environmental variables at Isla de la Plata. The primary source of variability in physical processes and biological production in the Humboldt Current upwelling system is the El Niño-Southern Oscillation (ENSO), where primary production declines during the negative El Niño phase, and increases during the positive La Niña phase. Data comprising the daily sightings of M. birostris were collected over a five-year period (2011-2015), and a generalised linear model was used to identify the effect of El Niño on the presence of individual M. birostris. Overall, month and ENSO activity explained 27.7 % of the variability in M. birostris sightings between years. The number of individual M. birostris sighted off mainland Ecuador was significantly higher during years with La Niña and neutral ENSO conditions in comparison to El Niño conditions, suggesting that overall food availability in this region is likely to be important for this species. To investigate the importance of local food availability and occurrence of M. birostris at Isla de la Plata, we determined near-surface zooplankton biomass, size structure and community composition in relation to M. birostris daytime foraging activity. When M. birostris was feeding there was higher zooplankton biomass in comparison to background non-feeding events. However, foraging activity was rarely observed at this aggregation site (6 % of all observations), which suggests that local food iii availability at Isla de la Plata during the day is not a major driver of M. birostris aggregative behaviour. In comparison, cleaning was the most common behaviour recorded during daytime hours (54 % of all observations), wi...