Date of Award

Spring 2021

Document Type

Open Access Dissertation

Department

Biological Sciences

First Advisor

Joseph M. Quattro

Abstract

Near infrared spectroscopy (NIRS) is a light spectroscopy method useful for non-invasively discriminating and quantifying chemical composition of a wide variety of substances. Recently-developed applications of NIRS to fish age estimation across a range of taxa have sparked intense interest in exploring the feasibility of its use for rapid age estimation in fisheries population management. In this pursuit, development of species-specific calibration models relating traditionally-derived age estimates (i.e., those estimated from growth band counts) to NIR spectral signatures from ageing structures is required to derive predictive models that can then estimate age from rapid scans of whole ageing structures alone. Otoliths and corresponding traditionally-derived ages of juvenile and adult red snapper Lutjanus campechanus were used to generate NIRS models for predicting both daily and annual ages. NIRS-predicted daily ages were accurate to within six days of traditional estimates and were not significantly different than traditionally-derived ages for juveniles aged 39 – 120 days when used to produce length-at-age models. NIRS-predicted annual ages were accurate to within approximately one year in fish aged 0 – 30 years, but prediction error rose substantially for fish aged 31 – 38 years. Across all models, age-related otolith morphometric dynamics changed the physical interaction of NIR light with the structures and impacted the resolution of age prediction models. When size and otolith morphometrics for a subset of otoliths (n=26) were standardized by grinding and subsampling a fixed mass from each for NIRS analysis, NIRS prediction error increased by approximately 30% but ages remained accurate to within 2 years of traditional ages; hence, otolith structure is of some importance to predictive models but ontogenetic compositional changes underlie most of the correlation of NIRS otolith spectral signatures with age. Protein concentration (% otolith weight) was positively correlated with traditional age, but the impact of this relationship on otolith spectral signatures was not easily discernable. However, comparison of otolith spectral signatures to those of two primary otolith constituents, calcium carbonate and type I collagen, revealed that absorbance features at characteristic wavenumbers for each constituent were correlated to NIRS otolith age prediction, providing the first insights to the NIRS age-prediction mechanism in otoliths.

Available for download on Monday, November 15, 2021

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