GROWTH RATE ESTIMATION OF HEXAPLEX (TRUNCULARIOPSIS) TRUNCULUS (GASTROPODA: MURICIDAE) BASED ON MARK/RECAPTURE EXPERIMENTS IN THE RIA FORMOSA LAGOON (ALGARVE COAST, SOUTHERN PORTUGAL)

Abstract

This study reports growth rates estimates for Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) from mark/recapture experiments carried out in the Ria Formosa lagoon (Algarve coast, southern Portugal). A total of 726 specimens (shell length and total weight ranging between 20.65–58.36 mm and 0.86–19.89 g, respectively) were marked with Dymo tape tags and released into a fish culture earth pond. During the marking process, no adverse effects on the whelks' health and behavior or immediate postmarking mortality were detected. Periodical recapture operations were undertaken using a traditional fishing gear designated locally as “wallet-line” and by hand gathering by scuba divers. A total of 170 whelks were caught, with a total of 216 recaptures (shell length and total weight ranging between 36.22–65.97 mm and 4.42–27.35 g, respectively), thus corresponding to a recapture rate of 29.8%. Despite the loss of one tag, all remaining tags were intact and easily readable. Marked individuals presented low monthly growth rates, in terms of shell length (1.0 mm/month or 2.3%/month), shell perimeter (2.0 mm/month or 3.1%/month) and total weight (0.7 g/month or 10.8%/month), which were highly variable between individuals and higher in smaller specimens. Data were used to estimate the von Bertalanffy growth parameters (length and weight) (K = 0.41, L∞ = 82.76, W∞ = 49.97 and t0 = −0.05). The growth rate of T. trunculus was compared with results obtained in similar studies with other gastropod species to evaluate its potential for molluscan aquaculture.