AGE READINGS AND ASSESSMENT IN COASTAL BATOID ELASMOBRANCHS FROM SMALL-SCALE SIZE-SELECTIVE FISHERY: THE IMPORTANCE OF DATA COMPARABILITY IN MULTISPECIFIC ASSEMBLAGES

Abstract

ABSTRACTAge readings and assessment of vertebral growth increments were obtained in four batoid elasmobranch species, namelyDasyatis pastinaca,Raja asterias,Torpedo marmorata, andTorpedo torpedo. Samples were obtained opportunistically from the bycatch of a size-selective fishery, such as local small-scale trammel net fishing, in the coastal waters of the Central Tyrrhenian Sea during 2019-21. We analysed the vertebrae by a simple and rapid method preventing staining phase and histological preparation to elucidate band pairs in all species studied. Consistency of age estimates was checked by controlling for agreement on band pair counts between and within observers, and by estimating the relationships between vertebral diameter and height, and body size of the animal. Based on these data, we developed a statistical routine to obtain multiple estimates of age and growth parameters for incomplete samples due to size-selective fishing. The acceptable agreement between and within readers and the increase in vertebral size with body size demonstrated the consistency of the method. Based on the results of Von Bertalanffy and Gompertz growth models, body size was a better predictor of age than vertebral size, and Gompertz models were a better estimator of age and growth parameters than Von Bertalanffy models. The estimated parameters (k and t0, kg and cg) matched the data available for the species studied in the Mediterranean Sea. In fact,D. pastinaca,T. torpedoandR. asteriasshowed the lowest (k = 0.05-0.12), intermediate (k = 0.112-0.19) and highest (k = 0.18-0.23) growth rate, respectively. Overall, the method proved effective both in delineating band pairs in vertebrae of different species by making use of only minimal optical equipment and a single reagent, and in reliably estimating the age and growth parameters of problematic samples due to size-selective fishing. The replicability of the method will help to collect comparable demographic data in similar samples from other areas of the Mediterranean, as well as in assemblages of different species from other places.