Age, growth and population parameters of the tropical sea urchin (Tripneustes gratilla) from the coastal waters of Sabah, Eastern Malaysia

Abstract

An investigation on the population parameters (growth, mortality, exploitation rate etc.) of the tropical sea urchin (Tripneustes gratilla) was carried out for one year from the monthly samples collected between January and December 2016 in Bum Bum Island, Sabah, Eastern Malaysia. A total of 615 live samples were collected during the experimental period and the mean length and weight were measured to be 8.36 ± 5.0 cm and 238.83±30 g, correspondingly. The relationship sandwiched between the total body weight and the total length of the species was estimated as TW=0.9563x2.5634 (R2=0.8407) from the linear regression graph. The estimated value of the total mortality at the end of the research was 4.94/yr, slightly exceeding the final result estimated for natural mortality which yields 3.24/yr at an average ambient temperature of 28°C in the study area. The exploitation rate (E) estimated for T. gratilla was 0.35, which was below the optimum exploitation level (E=0.50). The Gulland and Holt plot, as well as Von Bertalanffy non-linear least square regression methods were used to estimate growth parameters. Monthly length-frequency numeric data were analyzed using FAO FISAT II software for generating and estimating the population parameters such as asymptotic (∞)) length, growth coefficient (K) and age; which were 12.38 cm, 1.7/yr, and 2 yrs, respectively. However, the recruitment pattern was observed to be increased gradually with the maximum recruitment peak between the months of October and November 2016. This is the first approach to study the detailed population dynamic of the economically important tropical sea urchin (T. gratilla) endemic to the region. However, the result so far obtained from this research would greatly be useful towards the understanding of the detailed population structure and growth patterns that will undoubtedly help us to develop captive breeding, seed production, culture protocols and conservation strategies of this high-valued species incommensurate with national and international perspectives. Keywords: Sea urchin, Tripneustes gratilla, population parameters, stock assessment, Malaysia