Development of a Computer-Aided Age Determination System: Evaluation Based on Otoliths of Bank Rockfish off California

Abstract

We have developed a computer‐aided system (Bony Parts) to analyze periodic bands in fish otoliths (or other structures) for age estimation. The image analysis program first scans the image of a thin otolith section, perpendicular to the bands specified by the user. Adjacent scans are averaged and filtered with Fourier transformation or spatial domain convolution. Bands of higher density are detected and are marked and summed on the screen. We evaluated this new technique using subsamples of thin‐sectioned otoliths from the bank rockfish Sebastes rufus. The time and effort for cleaning, preparation, sectioning, and mounting are the same for both traditional and computer‐aided techniques. The computer‐aided technique reduced the time and tedium of counting bands, yet still allowed the user to interactively make subjective decisions about aging criteria. Both approaches produced similar readings, but computer‐aided estimates were more precise than traditional readings and required less analysis time. Thus, this new technique allows sample size and precision to be increased for a given amount of effort. Use of this new technique to age 1,897 sections produced von Bertalanffy growth equations that indicate female bank rockfish grow to a larger theoretical maximum size than males (L∞ = 500.7 mm versus 438.1 mm total length) but grow at a slightly slower rate (K = 0.054 for females versus 0.073 for males).

Radiometric age confirmation and growth of a deep-water marine fish species: The bank rockfish, Sebastes rufus

“…The parameters of the von Bertalanffy growth function reported by our study for S. rufus were similar to those from computer-aided ages (Cailliet et al, 1996), yet differed from those of Piner et al (2000), who reported L ∞ = 456 mm FL (480 mm TL), K = 0.09 for females and L ∞ = 403 mm FL (423 mm TL), K = 0.13 for males (see Love et al, 2002 for FL to TL conversion). All three studies were limited to length and age data from commercial landings, which lack young fish, and therefore do not necessarily represent population growth.…”

Age, growth and validation of otolith morphometrics as predictors of age in the forkbeard, Phycis phycis (Gadidae)

“…However, IAPE (4.2%) and CV (6.0%) for averaged readings between our two readers are still lower than the average values obtained in many ageing studies (Campana, 2001). In addition, we used digitized pictures instead of stereo microscope readings and according to Cailliet et al (1996), this could also result in a higher precision of age estimations. Repeated observations under the stereo microscope can be affected by different light conditions and placements of the otoliths, none of which affect images (Fossen et al, 2003).…”

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

“…Image analysis has been recently employed for detecting the annular and daily rings of otoliths. 15,17,18 However, the image analysis was used as a supplementary tool in age determination, not as a tool to read automatically. In the present study, we attempted to use image analysis software (NIH Image) as an auto-counting tool of age to develop a method of image analysis which had nearly equal accuracy to that of an experienced age-reader.…”

“…Although Beamish and Fournier (1981) 14 proposed a way to evaluate the precision of readers rather than the accuracy, 15,16 the true ages of specimens were necessary information when we compared the abilities (or the accuracy of readings) of the age-readers to determine ages correctly. Unfortunately, we mostly did not know the true ages of fish.…”