Guillen C., Rodriguez-Dominguez G., Avila-Poveda O.H;

Growth is an important life history trait that can be related to environmental features or can be implemented to characterize populations. This study examined growth by Schnute growth models based on length data for an edible intertidal invertebrate with indeterminate growth: Chiton articulatus. The geographical distribution of this species extends within the Mexican tropical Pacific from southernmost Oaxaca State (15° N) to northernmost Sinaloa State (23° N). From the length data of 470 organisms sampled monthly along a year (October 2015 to October 2016), several growth parameters (population size, number of size groups, number of cohorts, growth rate, and longevity) were evaluated for the northernmost adult populations of C. articulatus that living on the boundary between tropical and subtropical regions. We hypothesize that growth parameters of this ectothermic intertidal species will display a slow growth rate, with a larger adult body size in this boundary region as compared with the southern one. It was possible to identify: an adult population size between 45.87 mm to 86.06 mm; between one to three size groups per month (with an average of two groups); a total of six cohorts in the year; and estimated longevity of 3.45 years or 41.5 months. The best growth model was the case 2 Schnute model and the growth rate of adult populations in Sinaloa was slow and approached an asymptote. This study complements previous growth assessments of Chiton articulatus in their southernmost distribution confirming the previous hypothesis and reinforces the use of length data and Schnute growth models in mollusk studies.

Acknowledgments: This research took place within the framework of the Project quitón del Pacífico tropical mexicano (see, DOI: 10.3897/rio.6.e60446); Specimen collection was done under a research permit (No. PPF/DGOPA-130/15) granted by SADER and CONAPESCA.