Age and Growth of Endangered Smalltooth Sawfish (Pristis pectinata) Verified with LA-ICP-MS Analysis of Vertebrae

Abstract

Endangered smalltooth sawfish (Pristis pectinata) were opportunistically sampled in south Florida and aged by counting opaque bands in sectioned vertebrae (n = 15). Small sample size precluded traditional age verification, but fish collected in spring and summer had translucent vertebrae margins, while fish collected in winter had opaque margins. Trends in Sr:Ca measured across vertebrae with laser ablation-inductively coupled plasma-mass spectrometry corresponded well to annual salinity trends observed in sawfish estuarine nursery habitats in south Florida, thus serve as a chemical marker verifying annual formation of opaque bands. Based on that finding and assumptions about mean birth date and timing of opaque band formation, estimated age ranged from 0.4 y for a 0.60 m total length (TL) male to 14.0 y for a 4.35 m TL female. Von Bertalanffy growth parameters computed from size at age data were 4.48 m for L∞, 0.219 y-1for k, and -0.81 y for t0. Results of this study have important implications for sawfish conservation as well as for inferring habitat residency of euryhaline elasmobranchs via chemical analysis of vertebrae.