Age determination, growth, mortality and age of first reproduction in adult Queen Conch, Strombus gigas L., off Puerto Rico

Abstract

Growth and mortality of adult Strombus gigas L. was studied in a population offshore of La Parguera, Puerto Rico. Adult queen conchs do not grow in shell length, but only in shell thickness. Growth in thickness of the flared shell-lip was measured during a 2-year mark-recapture study and modelled using the von Bertalanffy growth function. Model parameters were K=0.3706 year −1 and L ∞ (asymptotic lip-thickness) =54.9 mm; the third von Bertalanffy parameter, t 0, cannot be obtained from mark-recapture data alone. Growth in tissue, meat and shell weights of adults were determined using the von Bertalanffy growth function in conjunction with regression equations for weights versus shell length and/or lip thickness. Total instantaneous mortality in adults, determined using von Bertalanffy parameters and lip-thickness frequency analysis, was 1.66 year −1. Subtracting a previous estimate of fishing mortality ( F=1.14 year −1) yielded a natural mortality ( M) of 0.52 year −1. Given an average age at maturation, defined by the formation of the flared shell-lip, of 3.2 years, the age of first reproduction was estimated at 3.6 years, but could be as much as 4 years.