Assessing residency time and habitat use of juvenile smalltooth sawfish using acoustic monitoring in a nursery habitat

Abstract

Highly productive, protected habitats have been shown to serve as nurseries for many marine fishes. However, few studies quantitatively measure the biotic characteristics that often drive a habitat’s function as a nursery. We used a combination of passive acoustic monitoring and quantification of biotic attributes to assess nursery habitat use of juvenile smalltooth sawfish Pristis pectinata. Acoustic receivers were deployed within Everglades National Park to quantify residency, identify the timing of emigration, and detect migration of juvenile smalltooth sawfish. Benthic grain size and organic content along with mangrove prop root density and limb overhang were quantified throughout the array to test for relationships between habitat attributes and smalltooth sawfish presence. Results indicated that sawfish moved quickly through deep water, narrow creeks, and rivers between shallow tidally influenced bays. A stepwise regression analysis of detections per hour indicated that sawfish had an increased probability of being encountered in areas with high prop root density. Observed residency within the nursery ranged from days to several months with some overwintering, which has never previously been documented in Everglades National Park. Given the large amount of individual variability of movement within the study area, future studies of juvenile smalltooth sawfish habitat in Everglades National Park should strive to investigate the relationships between occurrence and other potential drivers of habitat use such as prey fish assemblage and relative flow at multiple spatiotemporal scales.