Integrating methods for determining length-at-age to improve growth estimates for two large scombrids

Ballagh, Aaron C. and Welch, David and Williams, Ashley J. and Mapleston, Amos and Tobin, Andrew and Marton, Nicholas (2011) Integrating methods for determining length-at-age to improve growth estimates for two large scombrids. Fishery Bulletin, 109(1), pp. 90-100.

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Abstract

Fish growth is commonly estimated from length-at-age data obtained from otoliths. There are several techniques for estimating length-at-age from otoliths including 1) direct observed counts of annual increments; 2) age adjustment based on a categorization of otolith margins; 3) age adjustment based on known periods of spawning and annuli formation; 4) back-calculation to all annuli, and 5) back-calculation to the last annulus only. In this study we compared growth estimates (von Bertalanffy growth functions) obtained from the above five methods for estimating length-at-age from otoliths for two large scombrids: narrow-barred Spanish mackerel (Scomberomorus commerson) and broad-barred king mackerel (Scomberomorus semifasciatus). Likelihood ratio tests revealed that the largest differences in growth occurred between the back-calculation methods and the observed and adjusted methods for both species of mackerel. The pattern, however, was more pronounced for S. commerson than for S. semifasciatus, because of the pronounced effect of gear selectivity demonstrated for S. commerson. We propose a method of substituting length-at-age data from observed or adjusted methods with back-calculated length-at-age data to provide more appropriate estimates of population growth than those obtained with the individual methods alone, particularly when faster growing young fish are disproportionately selected for. Substitution of observed or adjusted length-at-age data with back-calculated length-at-age data provided more realistic estimates of length for younger ages than observed or adjusted methods as well as more realistic estimates of mean maximum length than those derived from backcalculation methods alone.

Item Type: Article
Title: Integrating methods for determining length-at-age to improve growth estimates for two large scombrids
Personal Creator/Author:
CreatorsEmail
Ballagh, Aaron C.
Welch, David
Williams, Ashley J.
Mapleston, Amos
Tobin, Andrew
Marton, Nicholas
Refereed: Yes
Journal or Publication Title: Fishery Bulletin
Volume: 109
Number: 1
Page Range: pp. 90-100
Date: 2011
ISSN: 0090-0656
Issuing Agency: United States National Marine Fisheries Service
Subjects: Biology
Ecology
Fisheries
Item ID: 8727
Depositing User: Patti M. Marraro
Date Deposited: 07 Jun 2012 14:56
Last Modified: 07 Jun 2012 14:56
URI: http://aquaticcommons.org/id/eprint/8727

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