Long-term random sampling confirms high-use areas and indicates declining abundance of juvenile smalltooth sawfish (Pristis pectinata) in Charlotte Harbor, Florida

Abstract

Abstract We evaluated 13 years of fishery-independent small juvenile (< 1.86 m stretch total length) endangered smalltooth sawfish sampling data from southwest Florida’s Charlotte Harbor estuarine system. From 2010 through 2022, within the sampling domain, estimated abundance declined, with an annual average across all seasons of 34 ± 11 individuals (range: 15–69). High-use areas were spatiotemporally stable and associated with well-oxygenated (dissolved oxygen > 7 mg/L), warm (25–33 °C), and brackish (salinity 5–27) waters between 5 and 15 km upriver along natural shorelines with concentrations of mangroves in both riverine nurseries. Adult female abundance, back-calculated from expected brood size (48 ± 16, range: 26–144) and stable age distribution (87 ± 30, range: 39–211), was low. Our findings of a significant declining trend in relative abundance of small juveniles and limited numbers of adult females are concerning considering ongoing threats from commercial shrimp trawl bycatch, destruction of nursery habitats, and major recent mortality events. Our model facilitates estimation of the number of individuals potentially exposed to harmful anthropogenic activities and identifies perennial high-use areas as priorities for permanent protection from habitat alterations and loss to promote recovery of the endangered smalltooth sawfish population in this unique estuarine system.