All nurseries are not created equal: large-scale habitat use patterns in two smalltooth sawfish nurseries

Abstract

Smalltooth sawfish Pristis pectinata use southwest Florida nurseries during at least their first 2 to 3 yr, and understanding region-specific habitat use patterns is important for effective management. Research occurred in 2 nurseries within the Charlotte Harbor estuarine system: the Caloosahatchee River, a highly human-altered nursery, and a more natural nursery, the Peace River. Between 2010 and 2013, a total of 148 juveniles ranging from 70.8 to 218.7 cm stretch total length were caught in gill nets, and 133 were acoustically tagged. The probability of encountering a sawfish during sampling was most influenced by season in both nurseries (highest during spring and summer), followed by dissolved oxygen in the Caloosahatchee River, and salinity and temperature in the Peace River. Temperature had lasting, atypical effects on movements when severe cold events occurred during the study. Outside of these disturbances, sawfish used all habitats available to them in both nurseries, but tended to reside in perennial high-use areas called nursery hotspots. Acoustic monitoring showed that juveniles gradually moved between 4 hotspots along a 20 river kilometer stretch of the Caloosahatchee River with seasonal changes in freshwater inflows or sometimes suddenly in response to large flow events. In contrast, sawfish in the Peace River remained associated with one nursery hotspot year-round. Reasons for these inter-nursery variations are attributed to differences in geomorphology and freshwater inflow regimes. This study illustrates that a full understanding of the life history of a species and the development of a conceptual model requires investigation of the species on a broad spatial scale. This consideration is important to avoid overgeneralization of habitat use patterns between nurseries.

Biology, ecology, and status of the smalltooth sawfish Pristis pectinata in the USA

“…Within the Caloosahatchee River nursery, juvenile sawfish distribution was significantly related to salinity; animals moved up the river in the dry season and down the river in the wet season to remain within their optimal salinity range of 18−30 ). Scharer et al (2017) also found that juveniles moved seasonally throughout the Caloosahatchee River, yet juveniles in the nearby upper Charlotte Harbor nursery remained associated with a single high-use area despite the same regional climatic conditions. The difference in habitat use between the 2 nurseries was attributed to the geomorphology and freshwater inflow regimes of the rivers.…”

“…The need for conservation and management of existing coastal habitats throughout the species' range is clear (Norton et al 2012, and conservation of specific estuaries in southwest Florida is especially important given their role as nurseries (NMFS 2009b, Norton et al 2012, Hollensead et al 2018). However, even within the large-scale nursery areas defined by Norton et al (2012), Scharer et al (2017) documented variability in habitat use by location, and thus individual nurseries may require specific management measures. Defining use of and protecting key habitat features at a finer scale within the larger nursery would have implications for management decisions, especially near highly populated areas like Cape Coral, Florida.…”

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

“…During random sampling, sites were selected from within 1 × 1 cartographic grids (1 square nautical mile) that contained water depths up to 3 m within the study area (see Scharer et al 2017 for details). Briefly, 2 random trips per month were conducted in northern Charlotte Harbor (8 sites per month; 2 nets per site).…”

“Urbanite” rays and sharks: Presence, habitat use and population structure in an urban semi-enclosed lagoon

“…The existence of ray or shark ''nursery grounds'' at shallow depths has long been described (Castro, 1993), where females and neonates are routinely encountered through time. Nurseries are, however, sometimes hard to define, with variation in their spatial configuration and environmental peculiarities (Scharer et al, 2017). Despite the fact that several criteria must be reached to label a place as a ''nursery ground'' (Heupel et al, 2007), different studies propose the existence of nurseries giving weight to diverse facts.…”