| || || Lethrinidae -- Fiji -- Age|
| || || Age, growth, mortality rates and reproductive biology of three Fijian emperor fishes (Pisces: Lethrinidae): Lethrinus harak Forsskal 1775, Lethrinus obsoletus Forsskal 1775 and Lethrinus atkinsoni Seale 1910 |
Author: Lasi, Ferral.
Institution: University of the South Pacific.
Subject: Lethrinidae -- Fiji -- Age, Lethrinidae -- Fiji -- Growth, Lethrinidae -- Fiji -- Mortality, Lethrinidae -- Fiji -- Reproduction
Call No.: Pac QL 638 .L48 L27 2003
Copyright:Under 10% of this thesis may be copied without the authors written permission
Abstract: Three species of emperor fish from the genus Lethrinus (L. hard, L. obsoletus and L. atkinsono were selected for study due to their importance in the artisanal and commercial 6sheries of Fiji The study aimed to establish some basic biological and ecological information which would be useful for the management and conservation of the stocks. More than 600 specimens of each species were collected between December 2000 and January 2002 fmm fishermen operating in the Swa lagoon. The lengths of 15 body parts were measured in an atfempt to establish a new key fbr identification. A dichotomous key for separating Fijian Lethrinus species was produced. The length-weight relationship (TL versus W) and size distributions were explored for each species. A proportion of the samples was aged by counting growth rings on sectioned saggital otoliths, and their demography was examined. Monthly values of the gonadosomatic index (GSI) along with histological analysis enabled the spawning season to be determined. Gut contents were analyzed for prey composition, and the ontogenetic variation in the diet of the three species was also investigated. Analysis of the lengths of the body parts indicates that bur (head, orbital girth and dorsal length), when expressed as percentages of total length (TL) are tenable fbr differentiation of the species. Each species had well developed growth increment bands that were suitable fbr demographic studies. The species were relatively long lied reaching 12,14 and 17 yr, respectively. Their growth coefficients (k) were 0.9, 0.28 and 0.36 yr-l, respectively. They became sexually mature at the age of 2 yr, 5 yr and 4 yr, respectively, and at a total length of 23.6 cm, 25.3 cm, and 25.4 cm, respectively. Their length-weight relationships were W = 0.0192 TL 231, W= 0.0184 TL,'~' and W = 0.0148 TL '01, respectively. The exploitation rate E indicates that L ufkinsoni may have already been over-fished (E = 0.74) while the other two species are optimally exploited (E = 0.51-0.52). L. obsoletus and L. harak spawned throughout the year with L. obsoletus showing a peak spawning period from July to October. Spawning for L ufkimoni occurred only from June to January, with a peak spawning period between J d y and September. Each species fed mainly on benthic invertebrates with diet overlap. However, there was a marked difference between the species in the prey importance. L. utkinsonii fed mostly on tellinid bivalves, L. obsoletus on crustaceans and annelids, while L. harak consumed both crustaceans and echinoderms in equal amounts (by weight).