Evidence of two-phase growth in elasmobranchs

It is often assumed that the von Bertalanffy growth model (VBGM) is appropriate to describe growth in length-at-age of elasmobranchs. However, a review of the literature suggests that a two-phase growth model could better describe growth in elasmobranchs. We compare the two-phase growth model (TPGM) with the VBGM for 18 data sets of elasmobranch species, by fitting the models to 36 age-length-at-age data pairs available. The Akaike Information Criteria (AIC) and the difference in AIC between both models revealed that in 23 cases the probability that the TPGM was true >= 50%. The VBGM tends to estimate larger L-infinity values than the two-phase growth model, while the k parameter tends to be underestimated. The growth rate in length-at-age appears tends to decrease near the age at first maturity in several species of elasmobranch. The importance of the TPGM lies in that it may better describe this aspect of the life history of many elasmobranchs. In this context, we conclude that the TPGM should be used along with other growth models in order to precisely estimate elasmobranch life history parameters.