New technique for determining age of coastal skates from Argentinian sea by digital image processing analysis: A preliminary study

Abstract

To understand dynamic populations of cartilaginous fishes age and growth studies have essential importance in the demographic analysis application, especially to estimate vulnerability to mortality by fishing. However, knowledge age of cartilaginous fishes have a serious inconvenient since in many opportunities the calcified structures, as vertebrae, must be stained with different techniques to identify rings of growth, and the effectiveness of each technique varies according to the study species. This problem would be solved using methods that allow identifying rings of growth with an objective technique such as digital image processing analysis. In the present work we performed a preliminary study using as model the Smallnose skate Sympterygia bonapartii (Rajidae). Corpus calcareum from small specimen does not have growth bands while the medium one has four bands and the large, six. The number of bands is related directly with the age of the specimens and is in good agreement with the visual counting made by two readers. The use of the algorithm to determine the number of bands in skates allows to be independent of the operator and to have a systematic method of measure.