Saint Peter and Saint Paul Archipelago is an important reproductive area for two shark and two ray species.

Between October 2010 and June 2015, 101 longline deployments were conducted during a fishery research survey across 60 days over 16 expeditions (Oliveira 2017). Of these, 65% occurred in the eastern part of the area, and 35% in the west. Each longline consisted of a 6 mm nylon monofilament mainline, 300–500 m in length, with 11–27 branch lines fitted with circle hooks (size 16 or 17) at their ends. Two fishing operations were conducted nightly: the first shortly after sunset, retrieved near midnight, and the second immediately after, retrieved before sunrise. The average soak time was four hours and 49 minutes (±1 hour and 38 minutes). In the 101 deployments, 129 sharks and rays were captured.

Silky Sharks comprised the majority of the captures (66.9%, n = 81), of which 76 individuals were measured and dissected (70–295 cm total length [TL]) (Oliveira 2017). Of these individuals, 24 were neonates/young-of-the-year (YOY) measuring <120 cm TL (Oliveira 2017). The smallest individual was a neonate with an umbilical scar measuring 70 cm TL. The size-at-birth of this species is 56–87 cm TL (Ebert et al. 2021). Historical data collected between September 1998 and April 2004 support the longstanding reproductive importance of this area (Hazin et al. 2007). From 96 Silky Sharks caught in this area, eight were classified as neonates/YOY (<120 cm) and ten females were pregnant. Embryo size from January–February varied widely (11–77.5 cm TL), suggesting no marked seasonal gestation cycle (Hazin et al. 2007).

For Cookie-cutter Shark, commercial fishing operations occurred at a maximum depth of 50 m during the day using handlines and trolling baited with flying fish and artificial bait, respectively (Santos et al. 2024). The survey spanned from March to September 2018, with effort distributed over four fishing cruises totalling 70 days at sea. A total of 200 individuals of five species of large pelagics (e.g., Wahoo Acanthocybium solandri and Yellowfin Tuna Thunnus albacares) were collected with bite marks from Cookie-cutter Sharks. The estimated size of sharks was calculated from the diameter of wounds using a linear regression of the shark’s mouth width to the TL of the sharks (Cadenat & Blache 1981; Muñoz-Chápuli et al. 1988). The length at 50% maturity (L50) for males was 34.6 cm TL and 41 cm TL for females (Compagno 1984). A total of 112 recent bites were used to estimate shark size. Cookie-cutter Sharks had an estimated length distribution from 6.2–23.3 cm TL and a mean estimated shark size of 13.8 ± 3.2 cm TL (Santos et al. 2024), indicating those were neonate/YOY. Size-at-birth for this species is 14–15 cm TL (Ebert et al. 2021). No other research focusing on Cookie-cutter Shark has been done in this area, but observations from researchers and fishers support their regular occurrence. Two juvenile Cookie-cutter Sharks were captured as incidental catch in the area, the first in August 2016 (~20 cm TL) and the second in August 2022 (23.5 cm TL) (Pinheiro et al. 2020; S Mendonça unpubl. data 2022). Size-at-maturity ranges between ~31–44 cm TL (Ebert et al. 2021). Between 2005–2015, during scientific cruises, at least 50% of big pelagic fishes captured had bite marks from Cookie-cutter Sharks (B Macena pers. obs. 2005–2015).

For Sicklefin Devil Ray, between December 2008 and June 2016, 38 expeditions of 15 days each (total = 570 days), were undertaken. The majority of expeditions (76%) occurred in the first half of the year – the period of greatest abundance of Sicklefin Devil Ray in the area (Mendonça et al. 2018; Mendonça et al. 2020). Sicklefin Devil Ray observations were performed mainly during the daytime and were restricted to one location on the western side of the islets. Observations were conducted from the deck of a fishing vessel or from an inflatable boat. Whenever the rays approached the survey point, free diving was conducted for underwater observation. From December 2008 to November 2010, sightings of 507 Sicklefin Devil Rays were recorded. Between December 2010 and June 2016, 320 sightings were recorded (Mendonça et al. 2018; Mendonça et al. 2020). Sex could be identified 361 times (43.6%), with females being more frequent (n = 215; 59.6%) than males (n = 146; 40.4%). The estimated disc width (DW) was recorded for 179 rays (22%) and ranged from 200–320 cm DW, with a mean ± SD of 260 ± 19 cm for both sexes pooled (Mendonça et al. 2020). Size at maturity is 270–280 cm DW for females and 198–250 cm DW for males (Notarbartolo-di-Sciara 1988; White et al. 2006; Rambahiniarison et al. 2018). Groups of 2–24 individuals were reported from 187 observations during the study (mean ± SD = 4.3 ± 3.6). The highest frequency of groups (n = 81) was observed in April and May. Solitary individuals were observed on 161 occasions (Mendonça et al. 2020). Evidence of mating was observed in both males (n = 7) and females (n = 6). In males, abrasions and swollenness/deformities were observed in the claspers while the females had scars in one or both pectoral fins. These potential mating scars were observed in April (2010, 2014, and 2015) and May (2014 and 2015), the same months when the largest groups were also seen (Mendonça et al. 2020). In addition to the mating scars, courtship behaviours were observed 14 times, mainly chasing trains, where sometimes the female was chased by one, two, or more males with the rays swimming in circles and overlapping with each other. Males made pelvic movements up and down, during courtship, in circles, apparently preparing for copulation although observations of chasing trains did not last more than a minute, with the rays moving away quickly (Mendonça et al. 2020). In some instances, during March and June, feeding behaviour (i.e., cephalic fins fully extended, and mouth opened) by single individuals or by groups of rays was observed concomitantly with other mobulid species that also feed on small pelagic organisms (Mendonça et al. 2018).

For Bentfin Devil Ray, one pregnant animal (180 cm DW) was caught by a commercial fishery boat in a small longline in March 2010. The left uterus contained one embryo at the initial stage of development (Mendonça et al. 2012). In May 2015, mating behaviour was recorded by drone during a scientific expedition, including both the ‘close following’ and attempted ‘pre-copulatory biting’ phase (McCallister et al. 2020). Additionally, aggregations of 3-15 animals, swollen claspers, and courtship events were observed between March and May in 2010, 2014, and 2015 (S Mendonça unpubl. data 2024).