Hinchinbrook-Palm Islands is an important reproductive area for three shark and five ray species.

The Herbert and Seymour rivers are important for early life-stage Bull Sharks (N Lubitz et al. unpubl. data 2025). Seven research fishing surveys using rod-and-line captured 28 neonates and young-of-the-year (YOY) (open and healed umbilical scars, 67–98 cm total length; TL) in these rivers between June 2021 to February 2025 (N Lubitz et al. unpubl data 2025). Most captures were during the austral summer which is the pupping season for Bull Sharks in this region (Lubitz 2023). Captures occurred between 8–16 km upstream from the river mouths and included freshwater sections of the rivers with notable absence of mangroves. The natal philopatry observed in females in eastern Australia means that multiple river systems along a coast can potentially be important for the reproduction of Bull Sharks (Tillet et al. 2012; Lubitz 2023). Genetic sequencing has shown relatedness between neonates/YOY in the Herbert and Seymour rivers, as well as between YOY from the rivers and acoustically tagged adults that exhibited year-round small home ranges within the marine parts of this  area,  further  supporting  natal philopatry (Lubitz 2023). No  neonate or  YOY were  caught  in nearby coastal waters outside the Herbert and Seymour rivers; only larger juveniles (>130 cm TL) and adults occur offshore around Hinchinbrook Island.

Blacktip Reef Sharks use the shallow reef flat of Pioneer Bay on Orpheus Island as a key reproductive area (George et al. 2019; Kanno 2023). Neonates and YOY occur year-round, with a peak in summer. Mating and parturition have been reported to occur between November–March (Chin et al. 2013; Schlaff et al. 2020). Long-term beach walk surveys confirm consistent use of the bay, with surveys often recording seven or more individuals between the mangroves and shallow beaches (Orpheus Island Research Station Staff pers. comm. 2025). Scientific fishing and acoustic tracking studies further demonstrate repeated use of this area by young Blacktip Reef Sharks. Between 2010–2013, 2017, and 2020–2021, sharks were captured using rod-and-line, multi-hook longlines, and seine netting, and were then monitored with passive and active acoustic telemetry (George et al. 2019; Schlaff et al. 2020; Kanno 2023). Each shark was measured, sexed, and assessed for maturity based on umbilical scar condition, body size, and clasper calcification (where possible). Between 2010–2013, 59 individuals were captured, of which 60% (n = 35) were immature (neonates, YOY, or small juveniles; 51.0–81.2 cm TL), found exclusively inside the bay. In contrast, any adults captured (99.8–145.2 cm TL) were recorded outside the bay (Schlaff et al. 2020). The regional size-at-birth estimate is ~50 cm TL, with maturity reached at 95–110 cm TL (Last & Stevens 2009), confirming these captures represented neonates, YOY, and small juveniles. Acoustic tracking also recorded six YOY (61.8–77.0 cm TL) tracked for >62 h in shallow (<1 m) water (George et al. 2019). Their movements were driven by the tide, swimming between mangrove roots at high tide and on the shallow reef flats at low tide (George et al. 2019). The adjacent mangrove root systems provide juveniles refuge from predators and access to foraging grounds, critical given the presence of large predators such as Great Hammerheads foraging in deeper reef flat areas (George et al. 2019; Kanno 2023; N Lubitz unpubl. data 2025). Adults are also regularly present in the area, likely migrating seasonally to inshore reefs for mating, although their home range extends further (Schlaff et al. 2020). Pioneer Bay is likely to be important for early life-stages of the species because of the proximity of refuge (mangroves) and foraging habitats (reef flat).

Multi-year recreational fisher knowledge with records from 2007–2025 indicates that neonate and YOY Scalloped Hammerheads occur regularly within the area (N Lubitz et al. pers. obs. 2025). Their size was visually estimated from photographs supplied by recreational fishers. Neonate and YOY were defined either by the state of the umbilical scar or by size, with individuals <80 cm TL classified as neonate or YOY. The size-at-birth for the species is 31–57 cm TL (Ebert et al. 2021).  In March 2025, a local fisher caught 12 neonate/YOY at Haycock Island, inside the narrow passage between Hinchinbrook Island and the mainland. At the same location, three YOY (56–80cm TL; healed umbilical scars) were tagged with acoustic tags in July 2025. Nearby, recreational fishers also reported neonates and YOY off beaches at the southern end of Hinchinbrook Island in March 2018, and near the Sugar Jetty in Lucinda, where they are observed, often in groups, annually between November–January. Anecdotal evidence suggests schooling behaviour as fishers always report catching multiple neonates/YOY. The entrance to, and the southern end of, the passage appears to be the key location for neonate/YOY Scalloped Hammerheads, as they were not captured elsewhere in this area despite widespread scientific fishing effort in 2023–2025. This location is characterised by turbid waters close to mangroves and rocky reefs, with availability of shallow and deep habitat close to each other. High turbidity was similarly an important driver of Scalloped Hammerhead juveniles in nearby Rockingham Bay (Simpfendorfer et al. 2014).

Spotted Eagle Ray YOY and juveniles are regularly observed on the Lucinda sandflats (B Nolan unpubl. data 2025). A total of 16 drone survey days between June 2024 and June 2025 recorded the species every day, with 97 individuals tracked that remained within 1.6 km of the high tide mark (B Nolan unpubl. data 2025). Size estimates were derived from still frames based on a calibrated relationship between drone altitude and pixel size. Size estimates of 20 individuals showed that most (n = 17; 85%) were YOY with a size of 60–85 cm disc width (DW). The size-at-birth for the species is 50 cm DW and YOY can be up to ~85 cm DW (Schluessel et al. 2010; Boggio-Pasqua et al. 2022). The other three individuals were juveniles <100 cm DW, further highlighting that this area is important for early life-stages of the species. YOY Spotted Eagle Rays were recorded across all survey months demonstrating their year-round presence in this area. Photo-identification confirmed that at least one individual remained in the area for six consecutive months from July–December 2024 and was resighted again in June 2025 (B Nolan unpubl. data 2025). These sightings indicate that the Lucinda sandflats constitute an important area for YOY and juvenile Spotted Eagle Rays, that may remain in the area for several months at a time. Additionally, two individuals (61 and 75 cm DW) were captured with seine nets at Lucinda between 2017–2018 (Crook 2020). Larger rays (>100 cm DW) also sometimes occur on the Lucinda sandflats, and three separate individuals with possible mating scars were observed in September 2024, including one individual with new mating scars on two days of observation (B Nolan unpubl. data 2025). Combined, this area is important for early life-stages and potentially for mating of Spotted Eagle Rays.

Giant Guitarfish neonates and YOY are regularly observed on the Lucinda sandflats in this area (Crook 2020; Myers et al. 2025a). Standardised seine net surveys from 2017–2019 captured 42 individuals ranging from 33–187 cm TL (mean 62 cm TL; Crook 2020), while 65 captures from 2022–2025 ranged from 30–115 cm TL (mean = 46 cm TL; Myers et al. 2025a). Out of the combined 92 captures (excluding re-captures of the same individual), 33 (30%) were neonates based on a size of 30–40 cm TL. Almost all others were YOY (n = 55; 60%) with a size of 41–65 cm TL. The size-at-birth for the species is 38–40 cm TL and YOY can be up to ~65 cm TL (White et al. 2014; Last et al. 2016). No adults were captured in either study, highlighting that this area is particularly important for early life-stages and juveniles of the species. Recaptures of neonates and YOY in different surveys support them remaining on the intertidal flat for at least 30 days post-capture (Myers et al. 2025a). Two Giant Guitarfish were captured in Pioneer Bay in 2016–2018 (Martins 2019), but they are uncommon outside the Lucinda sandflats. Acoustic tracking of three adult Giant Guitarfish (220–280 cm TL) shows that some individuals remain resident for multiple years in the larger area around the Lucinda sandflats (N Lubitz unpubl. data 2025), indicating that mating and/or pupping may also occur here.

Australian Whipray neonates and YOY are regularly observed in this area year-round. The species is one of the most common ray species across drone transect surveys, with 27 surveys each at Lucinda and Orpheus Island (Hazard Bay and Pioneer Bay) yielding a total of 230 observations during May–October 2021 (Myers 2024). Captures of at least 57 individuals using seine netting from 2022–2024 showed that around one third (18 individuals) were neonates or YOY with a size of <40 cm DW (Crook 2020; Myers et al. 2025b). Size-at-birth for the species is 35 cm DW (Last et al. 2016). Five active acoustic tracks of neonate and YOY individuals <40 cm DW show this species makes predictable tidal movements to and from the intertidal zone and spends 100% of their time in the shallows at Lucinda (Crook 2020). Additionally, 32 active drone tracks from 2018–2019 showed that 35 individuals <54 cm DW spent 100% of their time in the shallows at Lucinda. These data highlight the importance of the Lucinda sandflats for early life-stages of the species.

Broad Cowtail Ray YOY and small juveniles are regularly observed on the Lucinda sandflats within this area (Crook 2020; Myers et al. 2025a). Between 2016–2018, seine net surveys captured seven Broad Cowtail Rays at Lucinda, ranging 29–50 cm DW (mean = 39.5 cm DW). The size-at-birth for the species is 18 cm DW and fast initial growth suggests a size-at-one-year of ~35 cm DW (O’Shea et al. 2013; Last et al. 2016). From 2017–2025, additional seine net surveys recorded at least 160 individuals between 29–68 cm DW (mean ± standard error = 39.5 ± 0.6 cm DW) (Crook 2020; Myers et al. 2025a). Considering the small mean size near the size-at-one-year for the species, many of these individuals were YOY and small juveniles. From 2017–2019, drone tracking of 65 rays confirmed all spent 100% of their time in shallow habitats on the Lucinda sandflats. Additionally, the species is regularly seen in Pioneer Bay, with underwater video surveys recording Broad Cowtail Rays in 31.2% of samples and drone surveys showing that the species comprised 28.8% of all rays recorded (Kanno et al. 2019; Martins et al. 2020a, 2022; Myers 2024). Active acoustic tracking of seven YOY and juveniles (29–50 cm DW) also demonstrated complete residency in the shallow waters of Pioneer Bay (Martins et al. 2020a, 2022). Young-of-the-year and small juvenile Broad Cowtail Rays demonstrate strong site fidelity, predictable tidal movements, and seasonal peaks in abundance in this area (Martins et al. 2020a; 2022). Refuge behaviour is a likely driver, as Great Hammerheads forage extensively on rays on these shallow flats (N Lubitz et al. unpubl. data 2025). Collectively, these studies show that Pioneer Bay (Orpheus Island) and Lucinda’s intertidal flats serve as predictable reproductive habitats for Broad Cowtail Rays.

Mangrove Whipray YOY are regularly observed in Pioneer Bay within this area. A total of 35 individuals (27–61 cm DW) were caught between April 2016–March 2018 using seine and dip nets (Martins et al. 2022). Given a size-at-birth of ~14 cm DW and a size-at-maturity of ~55–65 cm DW (Last et al. 2016), as well as growth rates from similar species suggesting a size-at-one-year of ~30 cm DW (O’Shea et al. 2013), these captures were almost all YOY and juveniles. Twelve individuals (29–54 cm DW) were captured and tracked with towed-float GPS telemetry, spending 100% of their time in shallow reef flat and mangrove-edge habitats (Martins et al. 2020b). Another 12 Mangrove Whiprays (31–35 cm DW) were also captured with rod-and-line or seine nets and monitored with passive acoustic telemetry between 2020–2021 (Kanno 2023). Fine-scale tracking of four of these small juveniles showed regular use of the intertidal flats and mangroves as refuge from predators (Martins et al. 2020b, 2022; Kanno 2023). Additionally, a scientific study captured 24 Mangrove Whiprays in Pioneer Bay in 2022, with 71% (n = 17) YOY or very small juveniles with a size range of 30–35 cm DW (Myers 2024).