Using growth ring formation to study growth patterns of exploited sea urchin (Loxechinus albus) populations

Abstract

The formation of growth rings on the genital plates of two exploited subpopulations of the sea urchin, Loxechinus albus, using mark-recapture methods, was studied. Regression models for ordinal data were used to analyze their variability, and its effect on growth patterns was evaluated by comparing parameters of the resulting growth models. The observed formation of growth rings in L. albus from January 2015 to February 2016 allowed to determine the sea urchins age with 90% accuracy in the Picuta subpopulation, while in the Westhoff subpopulation, age was determined correctly in only 77% of cases, with a significant percentage of sea urchins over 50 mm TD that did not form new rings, suggesting precaution to estimate age using growth rings formation in sea urchins. The particular hydrodynamic characteristics of Picuta and their effect on the sea urchin distribution, could explain the observed growth rate stability despite 40 years of intense fishing. Westhoff, a system where only shallow subpopulations of sea urchin have been recorded, showed growth rate changes possibly associated with size-age truncation resulting from the fishing selective effect. Implementation of monitoring in non-fishing areas where trends in the local population can be followed, would help to identify key processes in L. albus population dynamics and design suitable management strategies of this socio-economically important resource.