Using a fisherman’s harvest in Acapulco, México, to characterize population structure, allometry, and body condition in the edible intertidal mollusc Chiton articulatus (Chitonida: Chitonidae)

Abstract

The large benthic mollusc Chiton articulatus, known locally as “sea cockroach”, is commercialized among tourists and locals at Acapulco Bay for its muscular foot (i.e., the edible meat), so it is harvested intensely. However, it has not been declared a fishing resource. Acapulco Bay is the main harvesting and consumption site for this species; thus, it is a proxy fishing area compared to other sites, where it is harvested sporadically. The population size structure, allometry (through length–weight relationship), and body condition of C. articulatus were characterized based on monthly harvest data obtained over course of one year in Acapulco Bay. The harvest was carried out by an exclusive chiton fisherman known as the “cucarachero” or “sea cockroach harvester”. The total harvest was 16,211 specimens/fisherman/year, with an estimate of 88–121 kg/fisherman/year of chiton. 97% of the total catch was concentrated between 30–60 mm in total length, i.e., the juvenile to adult stages. The length–weight relationship showed positive allometry during the sub-juvenile to juvenile stages (b = 3.16) but negative allometry during the subadult (b = 2.51) and adult stages (b = 2.84). The entire size range showed negative allometry (b = 2.78), which is consistent with an indeterminate length growth. The body condition “K” ranged on average between 16.3 and 20, showing significant differences between class intervals; however, over time, three condition periods were generated that related to the reproductive season and feeding of the species. While the size structure of C. articulatus in Acapulco appears to be stable over time, the size classes at sexual maturity are strongly harvested, which could lead to a depleted population structure. Currently, 15 fishermen collect chitons in Acapulco, collectively representing approximately 1.5 ± 0.3 tons/year. This information could be useful for making future management decisions related to the harvest of the species and establishing catch quotas.