Elasmobranchs (sharks, skates, and rays) are an evolutionarily conserved, diverse, and threatened vertebrate group (Dulvy et al., 2021; Sherman et al., 2023). Threats encompass direct and indirect fisheries activities (Worm et al., 2024), ocean warming (Rosa et al., 2017; Osgood et al., 2021), and habitat degradation, including disturbances to coastal breeding and pupping grounds (Sherman et al., 2020; Simpfendorfer et al., 2023).

Elasmobranchs have developed nine distinct reproductive strategies (Awruch, 2015) over their 400-million-year evolutionary history (Kriwet et al., 2008). Batoids, the most diverse group of cartilaginous fishes (Aschliman et al., 2012), comprise four orders, 23 families and 663 species, with many more yet to be described (Last et al., 2016a). While the largest order, Rajiformes (skates), is strictly oviparous, the remaining orders (Myliobatiformes, Rhinopristiformes, and Torpediniformes) are viviparous, with lecithotrophic and matrotrophic modes of reproduction (Conrath and Musick, 2012; Awruch, 2015). Myliobatiformes, including the family Dasyatidae (stingrays), rely on lipid histotrophy via trophonemata. Stingrays contain 19 genera, 86 extant species (Last et al., 2016a), and represent the most abundant group of rays occurring in tropical and subtropical coastal waters (White and Dharmadi, 2007). Stingrays produce broods of one to 10 with gestation periods up to 11 months, while smaller tropical species have shorter gestation periods of three to six months (Fahy et al., 2007; Pierce et al., 2009; Mull et al., 2010; Furumitsu et al., 2019). The duration of reproductive cycles varies among stingrays (Walker, 2020), and annual and biannual cycles have been confirmed in wild populations (Ramírez-Mosqueda et al., 2012; Schieber et al., 2023). However, batoid ecology and life history are comparably less understood than in sharks (Bräutigam et al., 2016; Martins et al., 2018; Jorgensen et al., 2022), with more than 250 Data Deficient species in the International Union for Conservation of Nature (IUCN) Red List (IUCN, 2023).

The Oceania fantail ray, Taeniura lessoni, (Last, White & Naylor, 2016) was described in 2016 (Last et al., 2016b), marking the second species within the genus alongside the widely-distributed bluespotted lagoon ray, T. lymma, (Forsskål, 1775). The disc width (DW), defined as the maximum distance between the wingtips (Serra-Pereira et al., 2010), ranges between 18 cm to 22 cm in female T. lessoni paratypes (Last et al., 2016b). The mature male holotype has a 20.9 cm DW, with large claspers measuring 21.2% of this width, while the immature paratype male measured 18.5 cm (Last et al., 2016b). T. lessoni is smaller than T. lymma and lacks the pair of vivid blue longitudinal stripes found along the tail. Also, the species appears to be restricted to Melanesia, including Papua New Guinea, Solomon Islands, Vanuatu, and Fiji (Last et al., 2016a; Hylton et al., 2017). T. lessoni inhabits shallow-water coral reefs, usually at depths of 20 m and less, typically shelters in caves during the day, and forages at night (Last et al., 2016a). In T. lymma, the embryos are initially nourished by the yolk sac and subsequently feed on uterine secretions (Hamlett et al., 2005; Musick et al., 2005; Abel and Grubbs, 2020). Fecundity has been reported with brood sizes of one to seven in wild individuals (Ferreira, 2013; Pereira et al., 2017). However, reproductive biology data for T. lessoni is lacking, and this species is classified as Data Deficient by the IUCN (Kyne and Finucci, 2018). In Fiji, T. lessoni is regularly observed during snorkeling trips and dives. Sightings are reported from across the archipelago (Glaus et al., 2024a), and the species is caught in small-scale fishing activities (Glaus et al., 2024b). To expand upon the limited life-history data for this range-restricted species, this study represents preliminary observational data focusing on the distribution and reproductive condition of female T. lessoni.

T. lessoni were observed in 71 surveys (67.6% of the total number surveys). Number of sightings by location varied: Sunrise Beach (n=47), Goat Beach (n=9), Lagoon Beach (n=6), Manta Beach (n=6), and Sunset Beach (n=3). At Sunrise Beach, mature females were sighted 38 times, six times at Goat Beach, and once each at Manta Beach and Sunset Beach. Mature males were observed three times each at Sunrise Beach and Goat Beach, and once at Sunset Beach. Neonates were sighted from early March onwards: six times at Lagoon Beach, two times at Manta Beach, and one time each at Sunrise and Sunset Beach ( Supplementary Figure 2 ). CPUE was highest at Goat Beach (0.9 T. lessoni observed per survey), followed by Sunrise Beach (0.7 T. lessoni observed per survey), Manta Beach (0.7 T. lessoni observed per survey), Lagoon Beach (0.6 T. lessoni observed per survey), and Sunset Beach (0.4 T. lessoni observed per survey).

Snorkelling recorded the highest number of sightings (n=48), followed by beach walks (n=15), and dives (n=8) ( Table 1 ). Mature females and males were mostly observed during snorkelling surveys, while immature specimens were predominantly sighted during beach walks ( Table 1 ).

At Sunrise Beach, four females in advanced gestation with conspicuously convex dorsa ( Figure 2 ) were recorded, occurring in shallow waters down to eight m depth. These four females were collectively recorded 24 times at the same site from the beginning of January until the end of March 2024. Individual 1 was recorded 13 times, Individual 2 six times, Individual 3 four times, and Individual 4 once, accounting for 63.2% of all female T. lessoni sightings at Sunrise Beach (n=38, Supplementary Figure 2 ). The DW of Individual 1 was estimated to be 24 cm to 25 cm, DW of the remaining three individuals in advance gestation was estimated between 21 to 25 cm.

The first indication of parturition was noted on February 29, 2024, when Individual 1 was photographed with a concave dorsum ( Figures 3A, B ). Over the following two weeks, Individual 3 (March 4) and Individual 2 (March 12) followed suit ( Figures 3C-F ). Additionally, Individual 1 exhibited a visible dermal abrasion on the left pectoral fin ( Figure 3B ; Supplementary Figure 3 ).

During the study period, the water temperature ranged from 28.22°C to 33.08°C. The lowest temperature was recorded at Sunrise Beach in January with an average of 29.94°C, while the highest temperature was measured at Sunset Beach with an average of 30.52°C in March.

This study represents the first documentation of advanced gestation in a stingray species in Fiji. We recorded four pregnant T. lessoni ( Figure 2 ), of which three gave birth between the end of February and mid-March, based upon photographic evidence ( Figure 3 ). The presence of neonates from early March onwards coincided with the estimated parturition period inferred from the rays’ condition. We were unable to determine the periodicity of the reproductive cycle and the gestation period, but T. lessoni may reproduce asynchronously and aseasonally. In a captive stingray species (formerly known as Dasyatis kuhlii and Neotrygon kuhlii) mating was observed immediately after parturition, suggesting the absence of a specific breeding season (Janse and Schrama, 2010). Based on bycatch data from eastern Indonesia, neither distinct seasonal reproductive cycles nor synchronicity in three stingray species could be determined, indicating a continuous reproductive cycle (White and Dharmadi, 2007). The dermal wound around the pectoral fin in Individual 1 ( Figure 3B ; Supplementary Figure 3 ) suggests a bite or abrasion from a pectoral grip or pre-copulatory biting, indicating that copulation may occur soon or immediately after parturition, as observed in captive T. lymma (Smith et al., 2017). Therefore, a continuous cycle with the potential for multiple pregnancies annually seems likely. However, long-term data, ideally combined with ultrasound diagnostics (Murakumo et al., 2020), are required to document gestation and to determine whether T. lessoni follows a continuous reproductive cycle or exhibits seasonal peaks around Drawaqa Island. To ensure practicality and minimal invasiveness, we determined maturity levels based solely on in situ size estimates. Assaying sex steroid hormones instead, enables accurate determination of maturity levels and depiction of cumulative proportions across different developmental stages (Mull et al., 2010). The surveyed sites on Drawaqa Island exhibit similar average temperatures ranging from 29.94°C to 30.52°C. Neonates and presumably immature T. lessoni were mostly observed during beach walks ( Table 1 ), and at Manta Beach and Lagoon Beach ( Supplementary Figure 2 ). Manta Beach and Lagoon Beach have a similar habitat composition with areas of sandy patches, rubbles, and seagrass assemblages, which could provide shelter for neonate T. lessoni (Dabruzzi et al., 2013). Sunrise Beach, predominantly frequented by mature females, has narrower expanses of sandy patches. Except for Individual 4, which was sighted only once, the other three females remained at Sunrise Beach, indicating repeated use of the area. Interestingly, mature males were only encountered seven times ( Table 1 ). One possibility to explain the skewed sex ratio towards females could be attributed to the increased energetic requirements of females during gestation (Jirik and Lowe, 2012), and thus the selection of areas that offer favourable conditions, including prey availability (Delpiani et al., 2013) and protection from predators (Martins et al., 2018).

Moving forward, a small-scale passive acoustic telemetry study, combined with ongoing environmental data collection, could help better understand presence, activity patterns, sexual segregation (Simpson et al., 2021), and seasonal or long-term site fidelity (Schlaff et al., 2014; Elston et al., 2021; Kraft et al., 2023). The waters surrounding Drawaqa Island are home to at least nine batoid species: T. lessoni (Data Deficient), Mobula birostris (Endangered), Aetobatus ocellatus, M. alfredi, Pateobatis fai, Taeniurops meyeni and Urogymnus asperrimus (all Vulnerable), Rhynchobatus australiae (Critically Endangered), and Neotrygon sp (Gordon and Vierus, 2022; Glaus et al., 2024a). Our preliminary data indicate that Drawaqa’s nearshore waters likely serve as pupping grounds for T. lessoni. Considering this, along with the diversity of species, the easy accessibility, and the continued monitoring setup, this location is ideal for further studies to deepen our understanding of ray ecology and biology.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation upon reasonable request.

Ethical approval was not required for the study involving animals in accordance with the local legislation and institutional requirements because the study was non-invasive and did not include any handling of living animals. The findings solely derive from visual observations.

KG: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Visualization, Writing – original draft, Writing – review & editing. TV: Conceptualization, Data curation, Validation, Visualization, Writing – original draft, Writing – review & editing. RM: Data curation, Funding acquisition, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing.