Out of the blue: uncommon records of pelagic elasmobranchs near the MoNa Cagarras Hope Spot, a no-take Marine Protected Area in Southwest Atlantic

ABSTRACT

Pelagic elasmobranchs are usually underreported in tropical coastal ecosystems, particularly in urbanized regions where long-term monitoring is lacking. This study presents six confirmed records of two pelagic species-Isurus oxyrinchus and Pteroplatytrygon violacea-documented between 1999 and 2025 near the MoNa Cagarras Hope Spot (a no-take Marine Protected Area) off the Rio de Janeiro coast, Brazil. These records combine opportunistic observations, artisanal fishery captures, and a stranding event. All three I. oxyrinchus individuals were identified as immature, whereas all P. violacea specimens were adults. Although occasional, these occurrences suggest that the area may function as a temporary refuge or foraging ground for broadly moving elasmobranchs at different life stages. Spatial proximity of the records to the Cagarras Archipelago reinforces the potential conservation value of this region, even for species not specifically targeted by local management plans. Our study highlights the importance of integrating unusual records into marine biodiversity assessments and recommends future research efforts focused on oceanographic influences, habitat use, and community-based monitoring strategies for threatened marine megafauna.

Keywords:
Elasmobranchii; Pelagic; Rio de Janeiro; Conservation

INTRODUCTION

Marine Protected Areas (MPAs) are essential tools for biodiversity conservation and for mitigating anthropogenic impacts on marine ecosystems (Enright, 2024). The Cagarras Islands and surrounding waters, located off the Rio de Janeiro coast, Southeastern Brazil, represent a prominent conservation site. Designated as a Natural Monument (MoNa Cagarras) in 2010 and recognized as a Hope Spot by the international nonprofit organization Mission Blue (https://missionblue.org/hope-spots/), this no-take MPA harbors high biodiversity, including reef fishes, marine invertebrates, seabirds, and cetaceans (ICMBio, 2020; Moraes and Seoane, 2013).

Despite its legal protection, the MoNa Cagarras is located near a densely urbanized area (i.e., the Rio de Janeiro metropolis), leaving it vulnerable to various anthropogenic pressures such as plastic pollution, sewage discharge, and artisanal fisheries (Neves et al., 2024). Oceanographically, this region is influenced by the South Atlantic Central Water (SACW) brought to the surface by seasonal upwelling events, especially between spring and summer months (Valentin, 2001). These events enhance local productivity and may drive the temporary coastal occurrence of pelagic and deep-sea species (Forde, 2005; Rykaczewski and Checkley, 2008).

Among the large pelagic species occasionally recorded in this region is Isurus oxyrinchus (shortfin mako), distributed throughout tropical and temperate oceans (Compagno, 2001; Garrone-Neto et al., 2013; Kohler et al., 2002). In Brazil, this species is mostly reported in offshore waters, with higher frequency in the southern and southeastern coasts (Amorim et al., 2002). Due to population declines driven by overfishing and bycatch, I. oxyrinchus is listed as Critically Endangered (CR) (Barreto et al., 2024) and as Endangered (EN) globally (Rigby et al., 2019).

Similarly, Pteroplatytrygon violacea (pelagic stingray) is a circumglobal, epipelagic species with sparse and often anecdotal coastal records in Brazil (Gomes et al., 2019; Menni and Stehmann, 2000; Vaske-Jr. and Rotundo, 2012). In the Southeastern Brazilian coast, pelagic stingray has been occasionally observed in oceanic waters and nearshore islands in Rio de Janeiro, with few documented appearances (Siqueira and Sant’Anna, 2007). These sporadic events may reflect ecological connectivity between oceanic and coastal environments and suggest potential influence of oceanographic drivers, such as upwelling and current-mediated advection (Wang et al., 2023). The species is currently listed as Least Concern (LC) by both national (ICMBio) and global (IUCN) conservation agencies (ICMBio, 2025; Kyne et al., 2019).

Given this scenario, the documentation of rare elasmobranch occurrences becomes particularly valuable, as it may provide insights into habitat use, oceanographic connectivity, and species distribution across ecotonal marine environments (Queiroz et al., 2016). Additionally, documenting threatened species contributes directly to conservation efforts by improving knowledge of their spatial occurrence (Dulvy et al., 2021). Such records are particularly informative in highly dynamic regions influenced by both natural variability and anthropogenic disturbances, including seasonal upwelling and proximity to urban areas (Rykaczewski and Checkley, 2008; Valentin, 2001). Thus, identifying and contextualizing the presence of broadly moving species in ecologically sensitive areas like the MoNa Cagarras may inform adaptive conservation strategies and contribute to a broader understanding of pelagic elasmobranch biodiversity in the poorly known Southwestern Atlantic. Accordingly, this study investigated the occurrence of unusually reported pelagic elasmobranchs near the MoNa Cagarras Hope Spot and explored the potential ecological and conservation implications of these records for regional oceanographic dynamics.

METHODS

UNDERWATER SIGHTING

An underwater visual record of Isurus oxyrinchus was obtained near the Cagarras Islands Natural Monument (MoNa Cagarras) and Ipanema Beach, Rio de Janeiro, Brazil, on March 23, 2025, during a recreational dive operated by the Macau Dive center. Photographic and video records were subsequently made available to the Instituto Mar Urbano (IMU) for scientific analysis and inclusion in its long-term underwater monitoring database.

IMU has conducted systematic underwater monitoring along the Rio de Janeiro coast since 1993, with intensified and regular survey efforts in recent years. The primary monitoring sites are located within the MoNa Cagarras, focusing mainly on Comprida and Redonda islands, while also including Cagarras and Palmas islands. Additionally, the institute frequently surveys other coastal regions such as Praia Vermelha, Cotunduba Island, Laje do Arpoador, and the Ipanema Underwater Outfall. These activities consist of approximately 5-10 dives per month across these various sites, contingent upon favorable environmental conditions (e.g., underwater visibility, sea state, wind, and precipitation). This long-term monitoring framework provides the contextual basis for interpreting sporadic records of large pelagic species in coastal waters.

Photographic and video documentation were obtained using a GoPro Hero11 camera. The footage was recorded at a 5.3K resolution and 30 frames per second (FPS) and subsequently analyzed to confirm species identification based on external morphological characteristics, including the presence or absence of claspers to determine sex. Total length (TL) was estimated in situ by comparing the specimen’s dimensions with the diver’s size and scuba equipment, with estimates further refined during post-dive analysis of the high-resolution footage.

FISHING RECORD

Records of elasmobranch species were compiled via opportunistic encounters and reports provided by artisanal fishers from Colônia Z-13, located in Copacabana, Rio de Janeiro. The landing of sharks and rays at Colônia Z-13 has been opportunistically monitored since 2018, with particular emphasis on the documentation of rare or infrequently recorded species. Within this monitoring framework, two occurrences of Isurus oxyrinchus were reported by local fishers-the first in 2018 and another in 2025. Additionally, two captures of Pteroplatytrygon violacea were documented by the same fishing community-one in 2019 and another in 2025. All records were supported by photographic documentation and verified information provided by fishers at the time of landing. Biological data, including TL and weight, were obtained by direct measurements using a measuring tape and a manual scale at the time of landing. Sex was identified by the presence or absence of claspers via direct observation of the pelvic fins. While most specimens were not deposited in scientific collections due to logistical constraints, two individuals remain preserved (frozen) for future laboratory analysis.

STRANDING RECORD

A photographic record of a stranded I. oxyrinchus was obtained from a report of an individual found on Ipanema Beach in 1999. Photographs were analyzed to assess external morphology and potential signs of injury. Due to the retrospective nature of this record, TL of the stranded individual was estimated by comparing its proportions with the human figure present in the photographic record. This method provided an approximate size rather than an exact physical measurement.

SPECIES IDENTIFICATION

Species identification was conducted based on morphological criteria, including body shape and coloration patterns. Identification followed the guidelines established by Gomes et al. (2019). Photographic evidence from all records was cross-referenced with regional and global identification guides to confirm species identity. Additionally, geographic coordinates for each record were obtained and all observation points were georeferenced and mapped using QGIS software (v. 3.28) to visualize the spatial distribution of specimens in relation to the MoNa Cagarras Hope Spot (Figure 1).

Figure 1
Geographic distribution of the recorded occurrences of Pteroplatytrygon violacea and Isurus oxyrinchus, obtained from the Instituto Mar Urbano image collection between 1999 and 2025, indicating the location of each individual record.

RESULTS

SHORTFIN MAKO (ISURUS OXYRINCHUS)

Four confirmed records of Isurus oxyrinchus were documented along the Rio de Janeiro coastline over a 26-year period. The earliest record occurred in July 1999, involving a stranded individual (180 cm total length, 45 kg) at Ipanema Beach, the shoreline of which faces the Cagarras Islands (Figure 2A). In September 2018, a juvenile female (74 cm, 2.4 kg) was captured by artisanal gillnet fishers near the Cagarras Islands (Figure 2B). A subsequent record from March 2025 corresponds to a juvenile female (160 cm) visually observed during a scuba diving expedition at Ipanema Beach (Figure 2C). The most recent record, obtained in October 2025, refers to a juvenile male (83 cm, 4.3 kg) captured near Cagarras Islands by artisanal fishers from Colônia Z-13, Copacabana (Figure 2D).

Figure 2
Documented occurrences of shortfin makos (Isurus oxyrinchus) close to the Cagarras Islands Hope Spot: (A) an individual stranded at Ipanema Beach in 1999; (B) a specimen captured by artisanal fishers affiliated with Colônia Z-13, Copacabana, in 2018; (C) an individual recorded during a scuba diving expedition at Ipanema Beach in March 2025; and (D) a specimen incidentally captured by artisanal fishers from Colônia Z-13, Copacabana, in October 2025.

Despite limited data, all four individuals were immature, suggesting a potential juvenile presence in nearshore waters adjacent to the Cagarras Archipelago. The combination of different observation methods-stranding, artisanal fishing, and recreational diving-also highlights the importance of integrating multiple opportunistic data sources into conservation monitoring efforts.

PELAGIC STINGRAY (PTEROPLATYTRYGON VIOLACEA)

Two records of P. violacea were confirmed in 2019 and 2025 in the oceanic zone surrounding the Cagarras Archipelago. The first, in April 2019, involved a female captured by gillnet near the Guanabara Bay mouth, east of the islands (Figure 3A). The second, from April 2025, describes a male captured by handline near the Rasa Island, a prominent rocky island in the same region (Figure 3B).

Figure 3
Documented occurrences of pelagic stingrays (Pteroplatytrygon violacea) near the Cagarras Island Hope Spot: (A) an individual captured by gillnet and landed at Colônia Z-13, in Copacabana, in 2019; and (B) a specimen caught using handline by artisanal fishermen and landed at Colônia Z-13, in Copacabana, in 2025.

Both events occurred in proximity to the interface between coastal and oceanic waters and involved artisanal fishing operations based at Colônia Z-13, Copacabana. These records constitute rare confirmations of this epipelagic species in Southwestern Atlantic shallow waters.

DISCUSSION

Juvenile and adult pelagic elasmobranchs, including Isurus oxyrinchus and Pteroplatytrygon violacea, may occasionally utilize coastal transition zones for feeding and temporary refuge (Afonso et al., 2022; Scales et al., 2014). At the MoNa Cagarras, the interface between coastal and oceanic waters creates productive ecological conditions, favoring aggregations of small pelagic fishes and planktonic organisms (Rykaczewski and Checkley, 2008; Valentin, 2001). These productivity fronts may attract both I. oxyrinchus, which preys on teleost fishes, and P. violacea, which forages on the water column and benthic substrates in shallow coastal zones (Menni and Stehmann, 2000). These records suggest that the region near the Cagarras Archipelago serves as a temporary refuge or foraging ground connecting offshore and nearshore environments.

The 26-year interval covered by the present records-spanning from 1999 to 2025-highlights the occasional yet recurring presence of I. oxyrinchus and P. violacea near the Cagarras Islands (Table 1). This temporal distribution suggests that this region is not regularly inhabited by these species but may be used opportunistically, depending on environmental and biological drivers (Gomes et al., 2019; Heupel et al., 2015). Although based on a limited number of events, the rarity and temporal spread of these records underscore the importance of documenting incidental encounters in data-deficient tropical regions. The low number of records over nearly three decades reflects the natural rarity of these species in coastal urban environments and highlights the challenges of monitoring highly mobile megafauna without long-term systematic efforts. However, this apparent rarity may also reflect significant gaps in data availability, particularly due to the absence of systematic monitoring programs and limited assessments of artisanal fishing activities in the area (Araujo et al., 2020). Such knowledge gaps are common for elasmobranchs in tropical regions and may lead to underestimation of their ecological importance and functional roles in coastal ecosystems (Dedman et al., 2024; Dulvy et al., 2021). Moreover, the diversity of observation methods-including stranding reports, artisanal fishery captures, and recreational scuba diving-highlights the value of integrating citizen science with long-term data sources to detect rare or low-frequency events (Blanco-Parra et al., 2022). Each approach presents inherent limitations and detection biases, but jointly they provide a broader understanding of elasmobranch presence and habitat use in data-deficient contexts. These complementary approaches provide a broader and more reliable perspective on the presence of rare species than any single method alone.

Table 1
Confirmed records of Isurus oxyrinchus and Pteroplatytrygon violacea along the Rio de Janeiro coast, near the MoNa Cagarras Hope Spot.

Date	Species	Location	Coordinates	Total Length (cm)	Weight (kg)	Sex	Observation
10/07/1999	Isurus oxyrinchus	Ipanema beach (P9)	22°59’14”S; 43°12’14”W	180	45	NA	Stranding
30/09/2018	Isurus oxyrinchus	Cagarras Islands	23°1’28”S; 43°11’28”W	74	2.4	Female	Captured by gillnet
23/03/2025	Isurus oxyrinchus	Ipanema Beach	23°0’38”S; 43°11’18”W	160	NA	Female	Diving
17/10/2025	Isurus oxyrinchus	Ipanema Underwater Outfall	23°0’31”S; 43°12’37”	83	4.3	Male	Captured by gillnet
08/04/2019	Pteroplatytrygon violacea	Guanabara Bay mouth	22°58’12”S;43°8’46”W	NA	NA	Female	Captured by gillnet
09/04/2025	Pteroplatytrygon violacea	Ilha Rasa	22°59’36”S;43°8’11”W	73	3.3	Male	Captured by handline

The apparent rarity of these species in Rio de Janeiro may be influenced by a lack of systematic monitoring. In the neighboring state of São Paulo, for example, Vaske-Jr. and Rotundo (2012) documented a higher frequency of P. violacea (n=15), including several inshore occurrences at depths between 9 and 50 m. Similarly, the species has been reported by Marion et al. (2014), in shallow waters (1.0 m depth) in Todos os Santos Bay, Bahia, reinforcing its capacity to transition between oceanic and coastal habitats across the South Atlantic.

Beyond observation methods, the spatial distribution of records-ranging from surf zones to offshore islands-highlights the ecological heterogeneity of the Hope Spot region and warrants further investigation of habitat features and depth gradients. This environmental complexity may influence species occurrence patterns at local scales and support multiple ecological functions, including foraging and refuge.

The biological features of the individuals recorded here also offer valuable ecological insights. All four specimens of I. oxyrinchus were immature, including three juveniles (two females and one male), whereas the P. violacea records comprised both a male and a female of adult size. This ontogenetic variation suggests that the area may serve as different ecological functions depending on life stage. While immature I. oxyrinchus may occasionally exploit these nearshore waters as opportunistic feeding or transient habitats, the occurrence of adult P. violacea individuals likely reflects transient use of the area as a stepping-stone within broader coastal-oceanic movements, rather than consistent foraging activity. Although the few available data require more records to classify the region as a nursery ground, the repeated presence of immature I. oxyrinchus in coastal environments highlights the need for further investigation into the functional role of these habitats for pelagic elasmobranchs. Similar patterns have been observed along other parts of Southeastern Brazil where oceanic species occasionally approach the coast during specific developmental or migratory phases (Costa et al., 1996; Costa et al., 2002).

A notable aspect of P. violacea records here is that both specimens were documented through artisanal fishing in April, making the seasonal transition from austral summer to autumn. This timing and method contrast with other regional reports that link species occurrence to distinct water masses. In São Paulo, Vaske-Jr. and Rotundo (2012) found 14 out of 15 P. violacea specimens captured during summer (December to March), a period characterized by the coastal intrusion of the nutrient-rich South Atlantic Central Water (SACW). Conversely, strandings of P. violacea and I. oxyrinchus in São Paulo have been reported primarily during the austral winter (June to September), explicitly associated with the intrusion of warm water masses from the Brazil Current (Garrone-Neto et al., 2013). This warm-water influence was also cited to explain a shallow-water fishing record from Todos os Santos Bay, Bahia, in September (Marion et al., 2014), where the presence of the species was attributed to the Brazil Current and Tropical Water. Thus, the occurrences documented here in April may represent a specific environmental window between the summer productivity peak driven by SACW and the winter dynamics often associated with warm-water intrusions from the Brazil Current.

As such, Marine Protected Areas such as MoNa Cagarras, even when not explicitly designed for elasmobranch conservation, may offer indirect benefits to threatened species by spatial overlap with ecologically relevant habitats. Protecting stepping-stone habitats within MPA networks is particularly relevant for species with broad distribution ranges and complex life histories (Heupel et al., 2015). Moreover, long-term monitoring programs in such regions can support the detection of shifts in occurrence patterns and species composition, particularly in response to anthropogenic pressures and climate variability (Dulvy et al., 2021).

Altogether, these findings reinforce the ecological relevance of the Cagarras Archipelago as a multifunctional habitat for pelagic elasmobranchs in the Southwestern Atlantic. Community-based monitoring programs and systematic partnerships with artisanal fishers and dive operators could enhance data collection on elasmobranch occurrences and guide adaptive management strategies for the MoNa Cagarras region. While the number of records remains limited, the integration of spatial, temporal, and biological data contributes to a broader understanding of habitat use by rarely observed species. Future research efforts should incorporate environmental drivers, fisheries interactions, and movement ecology to clarify the role of transitional coastal habitats in the life cycles of I. oxyrinchus, P. violacea, and other large broadly moving marine fauna. Despite these contributions, additional records will be necessary to strengthen ecological interpretations and confirm the patterns suggested here.

CONCLUSION

The present study documents six confirmed occurrences of pelagic elasmobranchs near the MoNa Cagarras Hope Spot, including four Isurus oxyrinchus individuals and two Pteroplatytrygon violacea specimens between 1999 and 2025. Although limited in number, these records highlight the ecological relevance of transitional coastal-oceanic zones and MPAs in Rio de Janeiro and demonstrate the value of integrating opportunistic observations into biodiversity monitoring frameworks. The recurrence of these species, including threatened taxa, in nearby areas of a no-take MPA reinforces the potential indirect role that protected areas can play in supporting the transient presence of broadly moving marine fauna, even when not specifically designed for such purposes. Further research should incorporate environmental variables and movement ecology to better assess the functional role of coastal habitats in the life cycles of pelagic elasmobranchs in Southwestern Atlantic.

DATA AVAILABILITY STATEMENT

All data are available from the corresponding author upon reasonable request.

SUPPLEMENTARY MATERIAL

No supplementary material is associated with this article.

ACKNOWLEDGMENTS

The authors thank Colônia de Pescadores Z-13 from Copacabana, Manasi Rebouças and José Manoel Rebouças for providing access to artisanal fisheries landings, the dive operator Macau Dive for making underwater images available for scientific analysis, Dhara Avelino Alves for support on map building, the Graduate Program in Neotropical Biodiversity (PPGBIO) for institutional support, and the Raias da Guanabara Project for the citizen science supported by Embratur.

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• AI USE STATEMENT
  Artificial intelligence tools (ChatGPT) were used exclusively to refine the English writing of this manuscript. The content was carefully reviewed by the authors to ensure consistency and correctness, and the authors are fully responsible for the final version of the manuscript.
• FUNDING
  This research was funded by Instituto Mar Urbano through sponsorship provided by the Instituto OceanPact and supported by a doctoral scholarship granted by CAPES (Finance Code 001).

Edited by

• Associate Editor:
  Rosangela Lessa

Publication Dates

• Publication in this collection
  24 Aug 2026
• Date of issue
  2026

History

• Received
  17 Dec 2025
• Accepted
  25 May 2026