The Gulf of Montijo is an important reproductive area for three shark species.

Recent evidence indicates that the Gulf of Montijo is a nursery area for Scalloped Hammerhead. In a study analysing artisanal fishery landings during 2013–2014, this species represented 87% of sharks landed (n = 1,104) in this area (Rodríguez Arriatti 2014). Neonates and young-of-the-year dominated the catch (99% of records) and there was a clear increase in mean size throughout the sampling period from 47 cm total length (TL) in April, 50 cm TL in June, 54 cm TL in July, 55 cm TL in August, and 63 cm TL in November (Rodríguez Arriatti 2014). The smallest recorded individual was 40 cm TL (Rodríguez Arriatti 2014). In another study also carried out in 2013–2014 (March 2013 to January 2014), Scalloped Hammerheads represented 84% of sharks captured (n = 440) by small-scale fisheries operating in the area (Vega et al. 2023). Size ranged between 34–103 cm TL, with a mean of 54.6 cm TL. Reported size-at-birth of Scalloped Hammerhead in the Eastern Pacific includes 47–55 cm TL for Ecuador (Estupiñán-Montaña et al. 2021), although sizes captured in the Gulf of Montijo suggest a smaller size-at-birth locally.

Based on the size ranges of catches of Scalloped Bonnethead, the area is considered a nursery ground for this small species of hammerhead. Information comes from the monitoring of artisanal fisheries during 2013–2014 (Rodríguez Arriatti 2014; Vega et al. 2023). The minimum, maximum, and mean size of Scalloped Bonnethead were: 29.3, 77.5, 61.7 cm TL (n = 19; Vega et al. 2023). Additionally, 33 individuals of Scalloped Bonnethead were caught in another monitoring study with a minimum size of 28 cm TL (Rodríguez Arriatti 2014). Reported size-at-birth is 28 cm TL in the Eastern Pacific (Gilbert 1967) and 22–23 cm TL in Colombia (Orozco Guarín et al. 2015).

There are several contemporary records (since the year 2000) of Largetooth Sawfish in the Gulf of Montijo with the largest clustering of records in Panama (n = 11 records from eight sites; López-Angarita et al. 2021). Largetooth Sawfish regularly occur in the area, with contemporary records from the years 2004, 2005, 2007, 2009, and 2015 (López-Angarita et al. 2021). These records originate from interviews with local fishers who were able to provide location-specific details of where sawfish were caught. Largetooth Sawfish is the only sawfish species occurring in the Eastern Pacific, is distinctive from other shark and ray species, and recognisable based on its elongated, tooth-studded rostrum.

Outside of the Eastern Pacific, it has been documented that Largetooth Sawfish spend the first 4–5 years in freshwater environments before moving to estuarine and coastal marine waters (except for the unique but depleted Lake Nicaragua population where individuals may have spent their whole life-cycle in freshwater; Thorson 1976, 1982; Thorburn et al. 2007). Apart from Lake Nicaragua, pupping is generally thought to occur around estuaries and river mouths (Kyne et al. 2021).

Despite the lack of further detail on the size classes of contemporary Largetooth Sawfish records in the area (i.e., if these were neonates, juveniles, or adults), several factors infer that the Gulf of Montijo is a reproductive area for the species: (1) the largest clustering of contemporary records anywhere in Panama; (2) known life-cycle; (3) known habitat preferences with extensive areas of core mangrove and riverine habitat in the area; and (4) documentation of contemporary records across multiple years. Largetooth Sawfish are locally extinct from much of the Eastern Pacific (Kyne et al. 2013; López-Angarita et al. 2021; Yan et al. 2021), therefore the temporal and spatial scale of contemporary records in the Gulf of Montijo is regionally, if not globally, significant.