Cadmium bioaccumulation in three benthic fish species, Salaria basilisca, Zosterisessor ophiocephalus and Solea vulgaris collected from the Gulf of Gabes in Tunisia

To select a marine teleost fish which can be used as a bioindicator of cadmium （Cd） pollution in the Gulf of Gabes in Tunisia, Cd concentrations in liver and gill were compared in three benthic fish species including Salaria basilisca, Zosterisessor ophiocephalus and Solea vulgaris. Fish samples were collected from three selected sites in the Gulf of Gabes, with different degrees of Cd contamination： the industrialized coast of Sfax （S 1）, the coast of Douar Chatt （S2） and the coast of Luza （S3）. The results shows that Cd concentrations in both sediment and water collected from S1 were significantly higher （t9 〈 0.0001） than those from S2 and S3. For each species, Cd concentrations, in both liver and gill, showed the decreasing order： S 1 〉 S2 〉 S3. The highest concentration of Cd was detected in the liver of S. basilisca, and only S. basilisca showed bioaccumulation factors （BAF） greater than 1 in all studied sites. In S 1 and S2, BAF values respect the following order： S. basilisca 〉 Z. ophiocephalus 〉 S. vulgaris. These results of significant bioaccumulation of Cd, in terms of hepatic concentrations and bioaccumulation factors, indicated that S. basilisca can be used as bioindicator to evaluate the evolution of Cd pollution in the Gulf of Gabes.

Age,growth and length-weight relationship of the rough skate,Raja radula(Linnaeus,1758)(Chondrichthyans:Rajidae),from the Gulf of Gabes(Tunisia,Central Mediterranean)

Objective:To investigate the length distribution,sex ratio,length-weight relationship,age and growth of Raja radula in the Gulf of Gabes.Methods:The age and growth characteristic of the rough skate(Raja radula)inhabiting in the Gulf of Gabes(Central Mediterranean Sea)was determined.A total of 1250 specimens were sampled.According to the marginal increment band its growth was annual.Results:The growth parameters were derived by using the von-Bertalanffy method and were separately evaluated as follows:TL∞=97.2 cm,K=0.15 y^(-1),t_(o)=0.35,and W_(∞)=5.28 kg,and TL∞=76.4 cm,K=0.22 y^(-1),to=0.16,and W∞=3.77 kg,for females and males respetively.The maximum age was 12 years for females and 10 years for males.Conclusions:Results from this research will provide a starting point to develop a management plan for the rough skate in the Gulf of Gabes.Further investigations are necessary to quantify the impact of the existing regulations on the population dynamics and recruitment patterns of this species in the region.

Age,growth and length-weight relationship of the white skate,Rostroraja alba(Linnaeus,1758)(Chondrichthyans:Rajidae),from the Gulf of Gabes(Tunisia,Central Mediterranean)

Objective:To investigate the length distribution,sex ratio,length-weight relationship,age and growth of Rostroraja alba in the Gulf of Gabes.Methods:This study estimated age and growth of the white skate,Rostroraja alba by counting vertebral band pairs from 112 specimens taken by commercial fisheries during 2006-2009 from the Gulf of Gabes(Southern Tunisia,Central Mediterranean Sea).Results:This is the first and only known information in regards to the age and growth of this species in Tunisia.Vertebra diameter was strongly correlated with total length and age,which were expressed by linear or cubic regression equations.The oldest female in this study was 35 years and 160 cm,whereas the oldest male was 32 years and 150 cm.The von Bertalanffy growth parameters were TL_(∞)=(202.26±3.40)cm,K=(0.040±0.038)/year and t_(0)=(1.84±0.01)10^(-1)/year for females and TL_(∞)=(198.60±3.61)cm,K=(0.060±0.076)/year and t_(0)=(1.28±0.04)/year for males.Conclusions:This study would be an effective tool for fishery biologists,managers and conservationists to initiate management strategies and regulations for the sustainable conservation of the remaining stocks of this species in the Gulf of Gabes(Southern Tunisia)ecosystem.

Distribution and morphometric characters of the Mediterranean longnosed skate,Dipturus oxyrinchus(Chondrichthyans:Rajidae)in the Gulf of Gabes(Tunisia,Central Mediterranean)

Objective:To investigate biometrics of Dipturus oxyrinchus(D.oxyrinchus),including length-weight relationships,total length(TL),disc width(DW),distance measured of snout tip to eye,width of the mouth,distance from snout tip to first dorsal,and the numeric characters in the Gulf of Gabes.Methods:Monthly sampling was conducted commercial bottom-trawl during December 2006 and January 2007,operating at a depth of 80-185 m.The TL,DW,distance of snout tip to eye,width of the mouth,distance from snout tip to first dorsal were measured to the nearest 0.1 cm and the weight was measured to the nearest 0.1 g.The parameters a and b were estimated by the least squares regression method.Results:A total of 520 D.oxyrinchus was ranged from 16.5 to 105.0 cm in TL and 30-5300 g in total mass were analyzed during this study.The overall sex ratio was significantly different from the expected value of 1:16(df=1,χ^(2)=3.38,P<0.05),and there was significant difference in the TL(t-test=16.53,df=520,P<0.05).There was significant difference in the regression slopes between sexes for the TL and DW relationship(t-test=17.53,df=520,P<0.05).The b value for the TL/weight relationship for males D.oxyrinchus sampled in this study(3.01)was lower than that for female(3.23).Morphometric characters were strongly positively correlated for TL.Conclusions:This study reported the first description of biometric relationships for D.oxyrinchus,which would be useful for the sustainable conservation of this rear fishery in the Gulf of Gabes and also form the basis for their inclusion in a regional security programme.

Soil Salinity Detection in Semi-Arid Region Using Spectral Unmixing, Remote Sensing and Ground Truth Measurements

Soil salinity is one of the serious environmental problems ravaging the soils of arid and semi-arid region, thereby affecting crop productivity, livestock, increase level of poverty and land degradation. Hyperspectral remote sensing is one of the important techniques to monitor, analyze and estimate the extent and severity of soil salt at regional to local scale. In this study we develop a model for the detection of salt-affected soils in arid and semi-arid regions and in our case it’s Ghannouch, Gabes. We used fourteen spectral indices and six spectral bands extracted from the Hyperion data. Linear Spectral Unmixing technique (LSU) was used in this study to improve the correlation between electrical conductivity and spectral indices and then improve the prediction of soil salinity as well as the reliability of the model. To build the model a multiple linear regression analysis was applied using the best correlated indices. The standard error of the estimate is about 1.57 mS/cm. The results of this study show that hyperion data is accurate and suitable for differentiating between categories of salt affected soils. The generated model can be used for management strategies in the future.