Malarrimo-Guerrero Negro is an important reproductive area for two shark species.

This area is one of two confirmed nurseries for White Sharks in the Northeast Pacific and the only one in Mexico (Oñate-González et al. 2017). Between 1999–2025, incidental catches of White Sharks were recorded across the west coast of the Baja California Peninsula (Santana-Morales et al. 2012; Oñate-González et al. 2017; García-Rodríguez et al. 2021; O Sosa-Nishizaki et al. unpubl. data 2026). Of 353 White Sharks recorded between 1999–2013 for which sizes were available, 333 (94.3%) were caught inside the broader Bahía Sebastián Vizcaíno region with 89% (n = 296) being categorised as neonate or young-of-the-year (YOY; Oñate-González et al. 2017). Between 2014–2025, ~10 individuals per year of these early life-stages were recorded from artisanal fisheries operating in the area (García-Rodríguez et al. 2021; O Sosa-Nishizaki et al. unpubl. data 2026). Neonate/YOY were defined as individuals with the presence of an unhealed/healed umbilical scar or because they measured <175 cm TL which is the reported size for YOY White Sharks (Cailliet et al. 1985; Malcolm et al. 2001). Although neonate/YOY White Sharks have been recorded along the coast of Bahía Sebastián Vizcaíno, the largest catches of these life-stages are concentrated inside this area, from the mouth of the Guerrero Negro Lagoon to Malarrimo, at depths <25 m (García-Rodríguez & Sosa-Nishizaki 2020). Acoustic telemetry of 13 neonate/YOY White Sharks tagged inside the area showed that early life-stages mostly use nearshore waters near the mouth of the Ojo de Liebre Lagoon (inside this area; García-Rodríguez 2020). White Sharks are present year-round in the area, but neonates/YOY are mostly caught between May–September (Oñate-González et al. 2017; García-Rodríguez 2020; García-Rodríguez & Sosa-Nishizaki 2020). Acoustic and satellite telemetry of YOY and juvenile White Sharks tagged in California have shown back and forth movements to Malarrimo-Guerrero Negro especially during autumn and winter (White et al. 2019; Logan et al. 2024), also highlighting the importance of this area for individuals coming from the other known nursery for the species.

Artisanal fisheries operating in the area were monitored monthly at landing sites between August–November in 2014 and 2015, and between August 2016–July 2017 (Sosa-Nishizaki et al. 2014, 2015; O Sosa-Nishizaki et al. unpubl. data 2026). During this monitoring, 115 Smooth Hammerheads were recorded of which 78 were measured (O Sosa-Nishizaki et al. unpubl. data 2026). Individuals ranged between 45–190 cm TL of which 26 (33.3%) were between 45–70 cm TL and were classified as neonate/YOY because they had an umbilical scar or because their size was close to the reported size-at-birth for the species (49–63 cm TL; Ebert et al. 2021). The rest of the individuals were juveniles as these were below the reported size-at-maturity for the species (~210–265 cm TL; Ebert et al. 2021). Although artisanal fisheries operate across the whole Bahía Sebastián Vizcaíno, early life-stages of Smooth Hammerhead were caught inside this area (near the Ojo de Liebre Lagoon mouth) and were recorded in August and September. This is the only location where neonate/YOY individuals have been regularly recorded along the west coast of the Baja California Peninsula.