Octopus (Octopus vulgaris, Mollusca, Cephalopoda) is an important and valuable fishery resource on the eastern and southern coasts of Tunisia, but its landings are highly variable. This paper explores the effect of environment on octopus catch per unit effort (CPUE) during a 12‐year period, through correlation analyses and the incorporation into surplus production models of sea surface temperature (SST) and rainfall data collected during cold (January–May) and hot (August–October) seasons. CLIMPROD software was used to select the appropriate model and fit it to the fishery and environment data. In both seasons, SST significantly contributed to CPUE variability; fishery production was influenced positively by cold season SST but negatively by hot season SST. Due to a poor fit with cold season data, the impact of rainfall was analysed only for the hot season, during which it has a positive effect on production. Results are discussed in view of the life‐cycle of octopus and the dynamics of the Tunisian fishery. This first study of octopus variability in Tunisia highlights the necessity to incorporate environmental influence into stock assessment and management advice.
The common octopus, (Octopus vulgaris Cuvier, 1797) is widely distributed through the world. It represents an important resource with high economic value. It is exploited by trawl and by other gears such as trammel net, pots and it is also captured by diving. Although the multitude of assessment techniques, few fisheries cephalopods were well managed. In Tunisia, common octopus (Octopus vulgaris) is captured particularly in southern coast and the Sahel defined by three regions (Mahdia, Sousse and Monastir). Our study constitutes the first assessment stock in Monastir situated in the mid of the eastern coasts of Tunisia. Using surplus production models, an under fishing state of Octopus in the East of Tunisia is shown. This study confirms also the necessity of the incorporation of environmental parameters for a better explanation of the variability of common octopus abundance and the importance of these results in the assessment and management of this species.
In frame of fisheries management, a stock assessment using surplus production models incorporating environmental parameters was dealt with one of the most important commercially crustacean fisheries resources along the Tunisian coast, the Melicertus kerathurus stock. The analysis was carried out for a period of 17 years with a database including fishing efforts, catches, catch per unit effort (CPUE) and sea surface temperature (SST). CLIMPROD is the software used to select the appropriate model and fit to the fishery and environmental data. Overall, SST was positively correlated to the yield and abundance index (CPUE) explaining 47% and 57% of their variability respectively, nevertheless. The incorporation of the SST in global model demonstrated that the SST influenced both the catchability and the abundance of this species separately. In fact the impact of SST leads to consider a production model impacted on the one hand by a linear relationship between the CPUE and the fishing effort, and on the other hand by also a linear relationship between the CPUE and the SST for both catchability or abundance of the species. The interpretation of global model with environmental parameters is changed with the incorporation of climate parameter.
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