Santa Catalina Island is an important resting area for two sharks and three ray species.

Horn Sharks rest in the area mostly during the day before moving to foraging areas at night according to active acoustic tracking and acceleration data loggers (ADL) deployed in 21 individuals during 2016 and 2017 in the area (Meese & Lowe 2020a). This process is also supported by calibrated laboratory experimentation for signal recognition of metabolic rates (Luongo & Lowe 2018). On average, females spent 88 ± 1.3% of the day resting while males spent 93.3 ± 2.2% of the day resting. Nighttime daily and core activity areas were significantly greater than during daytime, confirming resting during the day. In addition, underwater visual censuses (UVC; n = 55) consisting of 100 m transects were conducted in summer 2016 and 2017 (Meese & Lowe 2020b). In these surveys, 73 Horn Sharks were recorded with a frequency of occurrence of 56.5% in 2016 and 59.4% in 2017. All individuals rested in water temperatures between 15.7–23.0°C. Immature Horn Sharks (<58 cm TL) rested in shallower and warmer sites nearshore compared to larger individuals that were found in deeper and colder offshore reefs in the area (Meese & Lowe 2020b).

Aggregations of mature female Leopard Sharks occur regularly in the area during summer (Hight & Lowe 2007; May 2022). Between July–August 2003, visual surveys (conducted three times per day for 34 days) recorded the presence of resting aggregations of Leopard Sharks inside the area with an average (± standard deviation) of 22 ± 8 individuals and a maximum of 36 sharks recorded (Hight & Lowe 2007). In addition, during summer of 2018 and 2019, drone surveys (n = 84) were conducted in two locations inside the area, recording aggregations of 60.1 ± 7.3 and 21.5 ± 7.3 individuals (May 2022). These aggregations were associated with warm waters (22–24°C). Sixteen Leopard Sharks were tagged with a mix of acoustic tags for passive tracking (between 2004–2005) and tags with sensors to record body temperature and depth during short periods (<20 days in 2004; Hight & Lowe 2007). Tagged individuals showed an increased fidelity to thermal refugees in shallow coves inside the area during the day, compared to night when they moved outside of the area. This same pattern was already described during summer 1993 when 10 Leopard Sharks were acoustically tracked (1–23 days; Manley 1995). Individuals had smaller activity spaces and smaller movement rates in the area during the day, before moving outside the area at night and returning to the area the following morning (Manley 1995). Female Leopard Sharks use shallow and warm coves (e.g., Big Fisherman’s Cove) in the area during the day to rest before they move to deeper areas at night to potentially forage. These shallow waters in the area may provide thermal advantages that potentially increases digestion and gestation rate (Hight & Lowe 2007).

UVCs conducted in summer and fall of 2013 and 2014 revealed that Bat Rays, Shovelnose Guitarfish, and Haller’s Round Rays rest in the area (Meese & Lowe 2019). UVCs consisted of belt transects spanning 0.02 km² and extended up to 165 m from the shore at depths <20 m. Daily abundances recorded in UVCs showed the presence of aggregations composed of 38 ± 29 Bat Rays, 18 ± 10 Shovelnose Guitarfish, and 26 ± 16 Haller’s Round Stingrays. The three species were found together resting in sandy substrates at temperatures between 18.0–18.2°C but Bat Rays were most abundant at seafloor temperatures of 20°C and also rested in areas with macroalgae coverage and seagrass beds (Meese & Lowe 2019). All these species have been regularly recorded resting in the area by citizen scientists between 2020–2025 confirming their regular presence in the area (iNaturalist 2026b, 2026c, 2026d). These species have been observed shuttling between habitat types, utilising different substrates for their ‘hunt warm – rest cool’ bioenergetic strategy (Meese & Lowe 2019).