Validation of auto-counting method by NIH Image using otoliths of white-spotted char Salvelinus leucomaenis

Abstract

SUMMARY : The ages of individual specimens of white‐spotted char Salvelinus leucomaenis, collected from the Furuu River in Hokkaido, Japan, were determined from otoliths using NIH Image. We employed two methods to determine age. First, for a surface method (traditional method), the ages were made from examinations of otoliths under a microscope by experienced readers A, B and an unexperienced reader C. Second, for an auto‐counting method, a computer program was used to detect the peaks from otolith images. We made a mathematical model to estimate the probability of a correct reading for each reader, using the results of the age determination and the per cent age agreement among readers. The ability to determine the age of white‐spotted char depended on whether or not the reader had ever previously made age determinations. The ability of auto‐counting method was below that of reader A (one of the experts), and the method was slightly superior to reader B (the other expert).

Otolith science entering the 21st century

“…Some of this research has been directed at better methods for visualising growth increments, whether through application of dyes and stains (Green et al 2002) or through the development of semi-automated image analysis methods for identifying and counting increments (Takashima et al 2000). Truly novel approaches have also been developed, such as a method for carrying out threedimensional otolith analysis (Hamrin et al 1999).…”

Ecological Informatics

“…At one level these have required or allowed interaction with the user to assist in the identification of increments (Macy 1995;Cailliet 1996). More advanced methods have sought algorithms that identified increments as minima and maxima in digital profiles of brightness level (Troadec 1991;Welleman and Storbeck 1995;Lagardère and Troadec 1997;Morison and Robertson 1997;Takashima et al 2000).…”

“…The signals are inherently noisy and the change in slope method for identifying peaks (e.g. Takashima et al 2000) requires specifying a particular search bandwidth. As increments usually become narrower towards the otolith margins, this bandwidth must be progressively reduced to work equally reliably on the broad inner increments, when growth is fast, and on the narrow outer increments, formed when growth slows.…”

Comparison of Two Viewing Methods for Estimating Largemouth Bass and Walleye Ages from Sectioned Otoliths and Dorsal Spines

“…Advancements in technology and subsequent reductions in cost have resulted in the increased use of digital images in the age estimation process (Santamaria et al 2009;Hansen et al 2012;Koenigs et al 2015). Digital images require less space for archiving structures, allow multiple readers to estimate ages for the same sample of fish without direct transfer of the physical structures, and allow for use of computer programs that can be used to automate the identification and enumeration of annuli (Welleman and Storbeck 1995;Morison et al 1998;Takashima et al 2000) or to expedite measurement of growth increments for back-calculation of fish growth (Santamaria et al 2009;Hansen et al 2012). However, digital images may not provide an exact reproduction of a structure as it appears through a microscope.…”

“…Rypel (2008) demonstrated that two readers replicated consensus ages for 76-100% of individuals across five fish species by using images obtained from a flatbed scanner, but consensus ages were determined by a different set of readers, and the agreement between ages assigned from scanner images and by viewing otoliths through a microscope was not provided for individual readers. Several studies have compared ages estimated from digital images using computer algorithms with estimates obtained by readers viewing the same images or by viewing calcified structures through the microscope (Welleman and Storbeck 1995;Takashima et al 2000;Fablet and Le Josse 2005), but none of those papers compared reader-based ages between the two viewing methods.…”