Coelho, R. Age and growth of Raja undulata Lacepède, 1802 from the South coast of Portugal: methods, determination and verification.

Due to their characteristic slow growth rate, low fecundity with delayed reproductive effort, geared towards the production of a small number of progeny after a long gestation period, elasmobranch fishes are highly susceptible to overexploitation. Although very little is known about its biology, the undulate ray, Raja undulata, is one of the more important elasmobranch fishes captured along the Portuguese South Coast. Some traditional elasmobranch vertebral enhancing techniques, namely alizarin red S, silver nitrate, cobalt nitrate, cedarwood oil immersion, paraffin impregnation and nitric acid decalcification were tested on whole, halved and sectioned vertebrae. Through the analysis of the percentage concordance, mean percentage error, coefficient of variation and the precision index, associated with each of these techniques, the alizarin red S coloration applied to sectioned vertebrae was determined to be the most efficient band enhancing technique for this species. We found that the way vertebrae are processed is a factor in the determination of the number of bands counted, and put forward the hypothesis that the most traditional method of using whole vertebrae might underestimate age. Growth modeling was based on age / total length (L) data and estimated by the Von Bertallanfy growth function, with statistically significant differences being recorded for males and females:

Males: Lt = 96,45[1-e-0,28(t+0,55)]
Females: Lt = 97,44[1-e-0,28(t+0,39)]
Joined sexes: Lt = 96,30[1-e-0,29(t+0,42)]

As expected for most elasmobranch fishes, growth coefficients (k) are low, associated with high asymptotic length (L¥) values. Evidence for the deposition of one hyaline band during the winter was found through the marginal increment analysis. However, no final conclusions should be taken because of the restricted sampling period. Nevertheless an annual pattern of deposition of one hyaline band during the winter and one opaque band during the summer is suspected. Through the analyses of the back-calculated growth with the Fraser-Lee, BPH (Body Proportional Hypothesis) and SPH (Scale Proportional Hypothesis) models, the verification of the estimated ages was not possible. In all age classes, back-calculated growth was lower than the one estimated by direct vertebrae readings. An explanation based on the back-calculated technique is put forward. Total Weight (Wt) / Length and Eviscerated Weight (Wev) / Length relationships were established and as for other species of the Raja genus, a positive alometric relation was found. Because no significant differences were found between males and females, equations were estimated for both sexes combined:

Wt = 0,0024L3,248
Wev = 0,0020L3,248