Cleveland Bay is an important reproductive area for six shark and two ray species.

Cleveland Bay functions as a communal nursery for multiple shark and ray species. Due to the highly productive environment, the abundance of prey and evidence of niche partitioning among species suggests that competition is reduced, allowing sharks and rays to coexist (Simpfendorfer & Milward 1993; Harry et al. 2011a; Kinney 2011; Knip et al. 2011a, 2011b; Chin 2013; Simpfendorfer et al. 2014; Tobin et al. 2014; Simpfendorfer 2022).

Between 1986–1990, historical data were collected from commercial gillnetters using 10–15 cm monofilament nets, research surveys using 5–15 cm monofilament gillnets, and incidental catches of demersal otter trawls (Simpfendorfer & Milward 1993). Additionally, between 2007–2014, fishery-independent surveys and observer data from vessels operating in the commercial gillnet sector of the Queensland East Coast Inshore Finfish Fishery were compiled to characterise the shark and ray assemblage in coastal bays spanning ~400 km of Queensland’s north coast (Harry et al. 2011a; Kinney 2011; Knip et al. 2011a, 2011b; Chin 2013; Simpfendorfer et al. 2014; Tobin et al. 2014; Simpfendorfer 2022). In the fishery-independent surveys, sharks and rays were sampled across size classes using benthic gillnets and longlines between dawn and dusk. A minimum of five longlines or four gillnets were deployed per surveyed day, with daily transects selected by randomisation (Simpfendorfer et al. 2014). Gillnets of 200 m (4-6.5’ mesh size) were set for ~1 h and checked every 15 min. Longlines (800 m mainline, gangions every 8–10 m, 14/0 baited circle hooks) were set simultaneously for ~40–60 min. Both gears were used in 0.5–5 m depth; longlines were deployed parallel to shore and gillnets perpendicular to shore or contours (Simpfendorfer et al. 2014). Captured sharks were identified, tagged, measured, sexed, and released. Life-stage (neonates, young-of-the-year [YOY], juvenile, mature) was assigned from length-at-age, umbilical scar condition, and clasper calcification (Harry et al. 2011a; Simpfendorfer et al. 2014).

Between 2007–2014, a total of 241 Pigeye Sharks ranging in size between 61–197 cm total length (TL) were recorded by fishery observers (n = 5) and captured during fishery-independent surveys (n = 236) within the area (Harry et al. 2011a; Knip et al. 2011a, b; Chin 2013; Simpfendorfer et al. 2014; Tobin et al. 2014). Neonates (n = 53, 22%) ranging in size between 61–80 cm TL were identified based on size (n = 7), presence of an open umbilical scar (n = 19), or a partial open umbilical scar (n = 27). Young-of-the-year (n = 42, 17.5%), ranged in size between 72.5–80 cm TL. Size-at-birth for the species is ~60–72 cm TL (Ebert et al. 2021) and YOY reach 80 cm TL (Tillett et al. 2011). Neonates and YOY were captured across years in 2007 (n = 1), 2008 (n = 5), 2009 (n = 24), 2010 (n = 12), 2011 (n = 4), 2012 (n = 16), 2013 (n = 14), and 2014 (n = 19). Although captures of these life-stages occurred almost every month of the year (except July, October, and November), 85% of captures occurred between January–March. Habitat use by YOY Pigeye Sharks (n = 34) was studied using acoustic telemetry with 58 receivers deployed in Cleveland Bay between January 2009–May 2010 (Knip et al 2011a). Neonates and YOY Pigeye Sharks use creek mouths as primary nursery areas, remaining resident for several months before gradually expanding their range into deeper bay habitats as they grow (Knip et al. 2011a, 2011b). YOY occupied significantly shallower and turbid waters than older juveniles, with a median depth of 2.05 m compared to 2.83 m in 2-year-old sharks and movements were influenced by tidal dynamics, remaining within shallow habitat as water depths fluctuated (Knip et al. 2011a). Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay contained a high abundance of early life-stage Pigeye Sharks (Harry et al. 2011a; Simpfendorfer et al. 2014).

Between 1986–1990, a total of 35 Creek Whalers were sampled. All animals were smaller than 58 cm TL and captured during the months of February, November, and December (Simpfendorfer & Milward 1993). Size-at-birth for the species is ~45–55 cm TL (Ebert et al. 2021) and YOY reach ~70 cm TL (Smart et al. 2013). Between 2007–2014, a total of 181 Creek Whaler ranging in size between 29–150 cm TL were recorded by fishery observers (n = 3) and captured during fishery-independent surveys (n = 178) within the area (Harry et al. 2011a; Simpfendorfer et al. 2014; Tobin et al. 2014). Neonates (n = 13, 7.2%) ranging in size between 50.5–55 cm TL were identified based on size (n = 8), presence of an open umbilical scar (n = 3), or a partial open umbilical scar (n = 2). Young-of-the-year (n = 49, 27%), ranged in size between 55.6–70.0 cm TL. Neonates and YOY were captured across years in 2007 (n = 9), 2008 (n = 7), 2009 (n = 17), 2010 (n = 2), 2012 (n = 5), and 2013 (n = 22). Although captures of these life-stages occurred almost every month of the year (except June, July, October, and November), 59.7% of captures occurred between March–May (Harry et al. 2011a; Simpfendorfer et al. 2014). Additionally, 10 Creek Whalers ranging in size between 68–137 cm TL (seven YOY, three immature) were acoustically monitored within Cleveland Bay between September 2012 to May 2014 (Munroe et al. 2015). Presence by individual in Cleveland Bay ranged from 1 to 452 days (mean ± standard error [SE] = 205 ± 53 days), residency index ranged from 0.002 to 0.740 (mean ± SE = 0.34 ± 0.09), and there was no significant relationship between residency and size (Munroe et al. 2015). All resident individuals exclusively used the eastern side of Cleveland Bay (within the area), spending most of their time in seagrass habitats, which are typically highly productive and may serve as an important foraging area for this species (Munroe et al. 2015). Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay contained a high abundance of early life-stage Creek Whalers (Harry et al. 2011a; Simpfendorfer et al. 2014).

Data on Blacktip Shark and Australian Blacktip Shark are grouped together as they are morphologically similar species and are indistinguishable in the field (Harry et al. 2011a). Based on molecular studies, these two species occur in approximately equal frequencies in northern Australia (Ovenden et al. 2010). Size-at-birth for Australian Blacktip Shark is 60 cm TL (Ebert et al. 2021) and size for YOY ranges between 60–70 cm TL (Harry et al. 2013). In contrast, Blacktip Shark size-at-birth is 38–72 cm TL (Ebert et al. 2021) and size for YOY is 83.2–89.9 cm TL (Smart et al. 2015). The length-at-age estimates for Australian Blacktip Shark were used for Blacktip Shark/Australian Blacktip Shark neonates and YOY (<70 cm TL), or the presence of open or partially open umbilical scars to ensure that no juvenile sharks were misclassified. Between 1986–1990, a total of 133 Australian Blacktip Sharks were sampled with ~126 being smaller than 70 cm TL and were mainly caught from November–February (Simpfendorfer & Milward 1993). Between 2007–2014, a total of 305 Blacktip Shark/Australian Blacktip Shark ranging in size between 49.5–170.0 cm TL were recorded by fishery observers (n = 1) and captured during fishery-independent surveys (n = 304) within the area (Harry et al. 2011a; Simpfendorfer et al. 2014). Neonates and YOY (n = 98, 32.13%) ranging in size between 49.5–71.8 cm TL were identified based on size (n = 53), presence of an open umbilical scar (n = 31), or a partial open umbilical scar (n = 14). Neonates and YOY were captured across years in 2008 (n = 41), 2009 (n = 7), 2010 (n = 5), 2011 (n = 8), 2012 (n = 13), and 2013 (n = 24). Although captures of these life-stages occurred almost every month of the year (except March, May–August), 81.4% of captures occurred between December–January (Harry et al. 2011a; Simpfendorfer et al. 2014). Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay and Repulse Bay contained a high abundance of early life-stage Blacktip Sharks/Australian Blacktip Sharks (Harry et al. 2011a; Simpfendorfer et al. 2014).

Between 1986–1990, a total of 146 Milk Sharks were captured year-round in the area, with ~15% (n = 10) of them presenting open umbilical scar and sizes ranging between 34–46 cm TL (Simpfendorfer & Milward 1993). Size-at-birth for the species is ~25–40 cm TL (Ebert et al. 2021) and YOY reach ~60–88 cm TL (Harry et al. 2010). Between 2007–2014, a total of 51 Milk Shark ranging in size between 46.3–91.0 cm TL were captured during fishery-independent surveys within the area (Harry et al. 2011a; Simpfendorfer et al. 2014). Young-of-the-year (n = 49, 96%) ranging in size between 46.3–88.0 cm TL were identified based on size. These individuals were captured across years in 2007 (n = 4), 2008 (n = 13), 2009 (n = 29), 2010 (n = 1), and 2011 (n = 2). Although captures of these life-stages occurred in most months of the year (except in January, February, June, and August), 57.1% of captures occurred between September–November (Harry et al. 2011a; Simpfendorfer et al. 2014). Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay contained a high abundance of early life-stage Milk Sharks (Harry et al. 2011a; Simpfendorfer et al. 2014).

Between 1986–1990, a total of 112 Scalloped Hammerheads were sampled in the area, with ~48% (n = 43) of them presenting open umbilical scar with sizes between 46–54 cm TL (Simpfendorfer & Milward 1993). Almost all captured individuals (~ 90%) were under 74 cm TL and were captured year-round except in October (Simpfendorfer & Milward 1993). Size-at-birth for the species is 31–57 cm TL (Ebert et al. 2021) and YOY reach ~78 cm TL (Harry et al. 2011b). Between 2007–2014, a total of 106 Scalloped Hammerhead ranging in size between 40–225 cm TL were captured during fishery-independent surveys within the area (Harry et al. 2011a; Simpfendorfer et al. 2014; Tobin et al. 2014). Neonates (n = 63, 59.4%) ranging in size between 40–59.9 cm TL were identified based on size (n = 34), presence of an open umbilical scar (n = 17), or a partial open umbilical scar (n = 12). YOY (n = 11, 110.3%) ranged in size between 57.2–73 cm TL. Neonates and YOY were captured across years in 2007 (n = 13), 2008 (n = 22), 2009 (n = 3), 2010 (n = 7), 2011 (n = 6), 2012 (n = 10), 2013 (n = 10), and 2014 (n = 3). Although captures of these life-stages occurred every month of the year (between 2007–2014), 80.3% of captures occurred between December–March. Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay contained the highest abundance of early life-stage Scalloped Hammerheads (Harry et al. 2011a; Simpfendorfer et al. 2014).

Between 2007–2014, a total of 89 Narrow Sawfish ranging in size between 66–148 cm TL were recorded by fishery observers (n = 32) and captured during fishery-independent surveys (n = 57) within the area (Harry et al. 2011a; Simpfendorfer et al. 2014; Adkins et al. 2016). One neonate measuring 95.5 cm TL identified based on the presence of an open umbilical scar was captured in the area. Young-of-the-year (n = 84, 94.3%), ranged in size between 66–148 cm TL. Size-at-birth of the species is 43–70 cm TL (Last et al. 2016) and YOY sizes are estimated at <150 cm TL, based on growth curves (Peverell 2009). Neonates and YOY were captured across years in 2007 (n = 2), 2009 (n = 26), 2012 (n = 1), 2013 (n = 53), and 2014 (n = 2). Although captures of these life-stages occurred every month of the year, 54.8% of captures occurred between February–March and 38.1% between June–August. Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay contained a high abundance of early life-stage Narrow Sawfish (Harry et al. 2011a; Simpfendorfer et al. 2014; Adkins et al. 2016).

Between 2007–2014, a total of 80 Giant Guitarfish ranging in size between 41.4–285.9 cm TL were recorded by fishery observers (n = 2) and captured during fishery-independent surveys (n = 78) within the area (Harry et al. 2011a; Simpfendorfer et al. 2014). Young-of-the-year (n = 20, 25%) ranged in size between 41.4–89.0 cm TL. Size-at-birth of the species is 38–40 cm TL (Last et al. 2016) and YOY are estimated at 40–90 cm TL (D’Alberto et al. 2019). YOY were captured across years in 2008 (n = 3), 2009 (n = 10), and 2010 (n = 7). Although captures of these life-stages occurred in February, March, May, July, September, and November, 50% of captures occurred in May. Among the coastal bays in the Townsville region across 400 km of coastline, Cleveland Bay contained a high abundance of early life-stage Giant Guitarfish (Harry et al. 2011a; Simpfendorfer et al. 2014). Further, a total of 15 Giant Guitarfish (5 YOY, 1 juvenile, 9 adult females) were acoustically monitored in the area during 2009–2012 (White et al. 2014). YOY ranged between 50.8–86.0 cm TL (White et al. 2014). Giant Guitarfish were monitored between one and 766 days (mean ± SE = 333 ± 69 days) and were present at the site from one to 198 days (mean ± SE = 73 ± 25 days). Although YOY and juveniles (<100 cm TL) had low residency indexes, philopatric behaviour was exhibited by adult females (six out of nine), leaving the bay in the first weeks of December prior to the wet season and returning in October the next year (White et al. 2014). Additionally, contemporary records of YOY (n = 4; <90 cm TL visually estimated) were collated from the citizen science database iNaturalist in 2023 (n = 3) and 2025 (n = 1). These records come from direct observations with photo evidence and corroborate the contemporary presence of early life-stages of the species in the area.