Demographics of Butterfly Fish, Heniochus acuminatus (Perciformes, Chaetodontidae) from the Gulf of Mannar, India

Abstract

Butterfly fishes are widely distributed throughout the Indo-Pacific Ocean and are often caught in large quantity by shrimp trawlers as a by-catch species. These fish are ecologically and commercially important, as they are ecological indicators of coral health and a major component of ornamental and by-product fisheries. However, owing to their low value for direct human consumption as a food, there is dearth of research on their demographics and life–history traits. The present study was therefore conducted using Heniochus acuminatus, one of the common butterfly fish that is captured as a by-catch in the Gulf of Mannar (GoM) to generate basic data on its demographic estimates. Specimens (n = 833) were collected monthly from the four reef-fish landing stations for two consecutive years and the demographic parameters were estimated using a FAO–ICLARM Stock Assessment Tool (FiSAT). Fish in the length class of 10–11 cm dominated the landings. The length-weight relationship (LWR) was defined as the equation, BW = 0.0234TL3.156 suggesting positive allometric growth pattern of H. acuminatus in GoM. Estimated demographic parameters (asymptotic length, L∞ = 17.85 cm) showed low growth rate and growth performance index (K = 0.95 and ϕ = 2.481 respectively) in study species. The estimated potential longevity (tmax) and the observed length at first capture (Lc) were found to be 3.15 years and 7.9 cm respectively. The higher natural mortality rate (M = 2.00 yr−1) than the fishing mortality rate (F = 0.39 yr−1) with exploitation level (E = 0.16) below the optimum level indicates that the state of the stock of H. acuminatus in the GoM is sustainable. The current study provides the first population demographic report of the genus Heniochus and is likely to have a significant conservation and commercial impact.