The Growth Rates of Raja Brachyura, R. Clavata and R. Montagui as Determined From Tagging Data

A method of determining growth rates from growth increments obtained by tagging is described. The increments are divided by length groups, for each of which a sequence of quarterly increments is calculated. These are combined graphically to obtain a growth curve from which von Bertalanffy growth parameters are calculated. The method is applied to results obtained from three species of rays, Raja brachyura, R. clavata and R. montagui, tagged in the Irish Sea and Bristol Channel; previously published growth data of embryos and immediate post-hatching young are used to allot absolute ages to the growth curves. Growth parameters obtained are, for R. brachyura, males, L_∞ = 115·0 cm, K = 0·19, $t¯0=−0·80yr$; females, L_∞ = 118·4 cm, K = 0·19, $t¯0=−0·80yr$; R. montagui, males, L_∞ = 68·7 cm, K = 0·19, $t¯0=−0·56yr$; females, L_∞ = 72·8 cm, K = 0·18, $t¯0=−0·37yr$; R. clavata, males, L_∞ = 85·6 cm, K = 0·21, $t¯0=−0·60yr$; females, L_∞ = 107 cm, K = 0·13, $t¯0=−0·60yr$