Growth rates of four Hawaiian deep slope fishes: a comparison of methods for estimating age and growth from otolith microincrement widths

Abstract

Two methods were used to estimate the age and growth of four Hawaiian deep slope fishes. Otolith daily increment width estimates from radial sections of sagittal otoliths were integrated over the otolith radius to approximate age by (i) dividing interval length (micrometres) by mean increment width (micrometres per day) and summing this quotient for consecutive 500- µm radial intervals (S. Ralston and H.A. Williams. 1989. Fish. Bull. 87: 1-16) and (ii) fitting increment width (y) versus otolith radius (x) to a Gompertz rate curve and calculating the inverse integral of this curve (M.K. Smith and E. Kostlan. 1991. Fish. Bull. 89: 461-472). The methods also differ in the way the age-length key is generated. Ralston and Williams' method uses integrated age versus a regression-based estimate of fish length at 500- µm otolith radial intervals; Smith and Kostlan's method uses estimated age versus actual fish length. Neither method of integration produced significantly different age estimates; however, the use of regression-based fish length estimates instead of sampled fish lengths resulted in significant differences between estimated growth curves. The minimum number of daily increment width estimates required as a function of otolith radius was calculated, on the basis of observed microincrement width variation.