Document
Metadata
Title
evaluation de stock de poulpe: octopus cyanea dans la region sud-ouest de madagascar
Authors
RABERINARY Danie
Research Topic
Abstract
n the south-western Madagascar, the octopus fishery is an important source of income, but it has
begun to encounter problems that have driven resources degradation. Thus, appropriate and
sustainable management should be considered to avoid the depletion of threatened octopus stock.
A reproduction and the current state study of the Octopus cyanea stock was conducted throughout
the southwest coast of Madagascar, from February 2012 to January 2015, to complete necessary
biological information for the resources management. The determination of the laying period is
realized from the analysis of the proportion of mature female individuals. The obtained result by this
percentage analysis is verified by the spatial and temporal variation of the sex ratio and gonadosomatic relation.
The results of this study have shown a possibility of laying all throughout the year with two major
peaks and this is identical in all area of the South-west of Madagascar. The first peak is in JulyAugust and the second, more intense, is from November to February. The smallest mature male
individual weighs 200g and the size to 50% mature is 512,46g. Female become mature from 600g
with 50% mature at 2653, 23g.
The study of the catch variation and the size distribution has enabled us to understand the difference
between the various zones of the region. Catch and individual weight analysis indicate that the
southern part of the region is the most productive. In fact, Southern zone still has octopus of large
individuals with average weight of 1.07 kg at the extremity south (South II) and 0.97 kg in the
northern part of the southern zone (South I), while the average individual weight in the northern area
is 0.94 kg and 0.90 kg around Toliara (center area). These variations could be conditioned by the
fluctuation of the environmental factors and demographic factors.
Analytical models have been used to understand the current situation of the stock. Cohort analysis
(VPA) allowed us to estimate the number of new recruits and corresponding fishing mortality values
(F). The result of the cohort analysis has shown different numbers of newly recruited individuals
during the three years of study with 1,092,499 in 2012, 1,142,975 in 2013 and 885,637 in 2014.
The Leslie depletion model consists to verify the number of new recruits at the beginning of each
year from CPUE and total catch variation. Thompson and Bell predictive model subsequently was
used to predict the stock level according to F variation. Octopus stock of the area is fully exploited
and increasing the current level of fishing effort to more than 50% may result overexploitation of
resources.
Volume
1
Date of publication
December 1, 2015
Institution (University)
Institut Halieutique et des Sciences Marines Toliara
Page numbers (pp)
158