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Int'l Journal of Marine Science 2012, Vol.2, No.8, 57
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59
of Meteorology), which play a role in increasing the
mortality of this species and so influence negatively
the recruitment. But no diminution of temperature for
cold season (January~May) was detected. Although,
rainfall was found to be weakly correlated with the
abundance of common octopus, but the diminution of
the quantities of precipitations during some years
(1998~2002), had a negative repercussion on yield,
which explain the decrease of production of common
octopus in Monastir from 1999 to 2006.
The incorporation of environmental factors in surplus
production model is a necessity to explain the
mechanism affecting the population dynamics of
Octopus vulgaris
. Hence, multidisciplinary and
multispecies approaches are fundamental in
management of common octopus stock (Guerra et al.,
2010). According to Marine Strategy Framework
(COM, 2008), recent directions incite researchers to
integrate ecosystem approaches. Furthermore, the
ignorance of historic characteristics of life cycle may
be the cause of biased estimation which has
repercussion on cephalopod fishing management.
Among these characteristics, the definition of stock
unity is fundamental for management purpose. In
addition to biological and genetic aspect, the paucity
data and sometimes the absence of these data are
crucial problems related to theories and models for
mono-specific population especially the yield data. In
fact, the coefficient of variation (CV) catch data had
the greater bias on the assessment than the CV of
fishing effort. According to recent literature for
assessment and management of such resource, we
recommend the integration of environmental factors in
model as a primordial step for further studies for the
importance of fisheries management and the
conservation of species.
Several studies consider environmental conditions as
endogenous to fishery models, but in most assessment
these conditions are taken to be exogenous to the
problem and consider that economic indicators are
dominant and containing more information to
traditional single-stock indicators (Simonit and
Perring, 2005).
But in cephalopod the relationship between population
and environmental factors were more studied. For
common octopus, no study is dealing with economic
approach even in Tunisia.
As perspective, for analysis of the actual situation, it is
crucial to combine the environmental and economic
data and integrate them in global model as a tool
which allows corrective action to take decision for the
management of stock.
3 Materials and methods
3.1 Data
The data used, were production and fishing effort
collected for the region of Monastir in the eastern
coast of Tunisia (Figure 2) from the official fishing
statistics of the national general direction of fishing
and aquaculture (DGPA).
Figure 2 Study area, the region of Monastir in the eastern coast
of Tunisia
Fishing data (production and effort) have been
recorded for the period of the fishing season of
common octopus (mid October/November to mid May)
since 1995 to 2006. The effort used is the number of
trips and landing is expressed in Ton.
Because of the lack of some data about effort,
estimations were done as shown and explained in
Jabeur et al (2010). In fact, official octopus effort was
corrected from a monthly coefficient which is
computed using available data and precise data
collected for some years of fishing effort in Monastir
recorded by official services of fishery. This