Determination of fish growth by back-calculation from scales, with application to haddock (Melanogrammus aeglefinus (L.)) of the Newfoundland area

May, Arthur W. (1964) Determination of fish growth by back-calculation from scales, with application to haddock (Melanogrammus aeglefinus (L.)) of the Newfoundland area. Masters thesis, Memorial University of Newfoundland.

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Abstract

Methods of determining age and growth of fish are reviewed. In particular, the scale method of ageing and procedures for back-calculation of growth from scales are reviewed in some detail, and are applied to haddock of the Newfoundland area. -- Plots of fork length on scale diameter are used to determine the body-scale relationship, and are found to be linear. Differences between the fitted regressions for the sexes, year-classes and areas are examined by analysis of covariance. It is concluded that a general body-scale relationship, having a regression coefficient of 4.62 and L-intercept value of 6.57 cm, provides an adequate description of the relative growth of body and scales in the area as a whole. -- The L-intercept value was used to correct the simple proportionality (Dahl-Lea) formula for back-calculation of growth. Values of back-calculated average lengths at age were slightly higher (of the order of 1 cm) than empirical averages. Lee's phenomenon, the apparent decline in average length at age when calculations are made from successively older fish, does not appear in its usual form in the data, but occurs in reverse form in growth calculations from the most recent year-classes. Differences in growth are found between immature and mature fish, males and females, year-classes and areas and possible reasons for these differences are discussed. Average lengths at age of Newfoundland area haddock are shown to be less than those for other areas of the northwest Atlantic over the range of ages compared.

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