Diel movements of juvenile smalltooth sawfish: implications for defining the size of a nursery hotspot

Abstract

Habitat use and movements of juvenile (<3 yr old) Critically Endangered smalltooth sawfish Pristis pectinata were studied in the Peace River nursery in southwest Florida to estimate the size of a known nursery hotspot (high-use area). A total of 23 smalltooth sawfish were tagged during the peak recruitment period of April and May 2014 and tracked until the end of September 2014 using passive acoustic monitoring. Active tracking was also used to estimate positions of individuals relative to the shoreline and major habitat types. During the day, sawfish <1500 mm stretch total length (STL; n = 11), representing <1-yr-old fish, and those between 1504 and 1881 mm STL (n = 12), representing ≥1-yr-old fish (1 to 3 yr old), remained along the northern shoreline of the river, in a protected cove. The younger age class remained closer (<25 m) to red-mangrove-dominated shorelines than did the older age class. At night, both age classes moved further away from the shoreline and away from the protected cove; the older individuals made the longest excursions (~5 km), toward the southern shoreline of the river. The discovery of these regular diel movements led to the expansion of the boundaries of the single recognized nursery hotspot in the Peace River, which was previously defined solely on daytime catch data. If another layer of protection is needed in the hotspots relative to other areas within the sawfish critical habitat, then defining the boundaries of the hotspots has implications with respect to management plans, federal permitting activities, and restoration opportunities.