چكيده انگليسي :
This study aimed to evaluate the quantitative (number of fish, catch figures and caviar harvest) and qualitative changes (sex composition, age and length) of sturgeons, as well as to calculate their catch per unit effort (CPUE), and investigate catch trends and spatial and temporal distribution of sturgeon in 2009 through 2012. The marine survey for sturgeon stock assessment was conducted in summer, winter and spring in the years 2009 and 2012 to estimate the relative and absolute abundance and percentage composition of each species in the Guilan, Mazandaran and Golestan Provinces. This survey was carried out in the Iranian waters of the Caspian Sea on board the Sisara2 (250 hp) and Guilan vessels (1000 hp) using trawl nets at 2-100 m depths. Trawling was carried out in 90 stations that were selected using a stratified random design. The number of stations in each scope was based on the area of the scope in terms of the total area. Trawling and sampling in shallow water up to 10 m were carried out using 9 m trawl nets whereas 24.7 m trawl nets were used for depths more than 10 m. Trawl surveys were carried out in the daytime. Trawling velocity was kept at 2.5-3 kts and trawls lasted half an hour in order to calculate abundance, and biomass of sturgeons using the swept area method.
Changes in sturgeon stocks in the Iranian coastal waters of the Caspian Sea were analyzed using different population parameters including catch figures, CPUE, length, age, weight, sex composition and weight of caviar. The biometry data of sturgeon caught were collected from all catch stations of the Northern provinces. CPUE in catch stations was estimated in terms of fishing boats, and on the basis of number of purse seine operations.
The population genetic structure of the Persian sturgeon (Acipenser persicus) in the 2, 3, 4 fisheries regions and Sefidrud River was investigated based on the DNA sequencing method during 2010 – 2013 sturgeon stock assessment in the south Caspian Sea . DNA samples were extracted using ammonium acetate, the quantity of DNA was measured at 260 and 280 nm using spectrophotometry by Nanodrop (ND 1000 model), and the quality was checked by 1% agarose gel electrophoresis. Two sets of mitochondrial gene (D-loop and cytochrom b) after synthesis were used for polymerase chain reaction (PCR). A Neighbor-Joining (NJ) tree was constructed for all haplotypes according to Kimura 2-parameter model using Mega Version 4.0.1, number of haplotypes, haplotype diversity (Hd) and nucleotide diversity and their corresponding variances, genetic divergence overall and between paired populations (Fst) by 10,000 permutations and exact test, the gamma distribution shape parameter for the rate heterogeneity among sites and nucleotide sequence, the historical demographic pattern of A.persicus using neutrality tests and mismatch distribution analysis (D test of Tajima and Fs test of Fu), also the concordance of the observed with the expected distribution under the sudden population model using the Harpending,s raggedness index (Hri) were analyzed. All calculations were conducted using ARLEQUIN version 3.11 and DnaSP 4.0.
In this study, some blood indices were studied with the aim at evaluating natural condition and sexing of wild sturgeon captured by trawl in Sea patrol during 2009 – 2012. After biometry of 84 Acipenser persicus with mean weight 1041.1 g, 14 Acipenser stellatus with mean weight 455.2 g and 4 Acipenser nudiventris with mean weight 614.5 g, blood samples were collected from them and serum separated. Hematological indices were studied based on standard methods. After biopsy their gonad samples were fixed in Buin’s solution and studied histologically based on routine experimental methods.
In Autumn 2009 totally 62 sturgeon specimens were caught including 51 A. persicus specimens, 9 A. stellatus and and 2 A. gueldenstaedtii specimens. The catch composition comprised 82.3% A. persicus, 14.5% and 3.2% A. gueldenstaedtii. In Winter 2009 totally 21 sturgeon specimens were caught including 14 A. persicus specimens, 2 A. stellatus, 3 A. gueldenstaedtii and 2 A. nudiventris specimens. The catch composition comprised 66.7% A. persicus, 9.5% A. stellatus, 14.3% A. gueldenstaedtii and 9.5% A. nudiventris . In Spring 2010 totally 14 sturgeon specimens were caught including 14 A. persicus specimens(100%). In Summer 2010 totally 14 sturgeon specimens were caught including 14 A. persicus specimens(100%). In Autumn 2011 totally 281 sturgeon specimens were caught including 256 A. persicus specimens and 25 A. stellatus specimens . The catch composition comprised 91.1% A. persicus and 8.9% A. stellatus. In Autumn 2012 totally 278 sturgeon specimens were caught including 193 A. persicus specimens and 85 A. stellatus specimens . The catch composition comprised 69.4% A. persicus and 30.6% A. stellatus. Relative abundance of sturgeons caught in bottom trawls in Autumn 2009 was 0.69, in Winter 2009 was 0.23, in Spring 2010 was 0.16, Summer 2010 was 0.17 , Autumn 2011 was 6.96 and Autumn 2012 was 7.03 specimens per trawl. Based on the calculations carried out in the marine survey in Autumn 2009 the estimated absolute abundance for sturgeons was about 3487 thousand. In the Winter 2009 total abundance was estimated 1175.8 thousand, and total biomass of sturgeons was estimated at about 312.161 tons. In the Spring 2010 total abundance was estimated 831.1 thousand, and total biomass of sturgeons was estimated at about 760.6 tons. In the Summer 2010 total abundance was estimated 779.2 thousand, and total biomass of sturgeons was estimated at about 855.0 tons. In the Autumn 2011 total abundance was estimated 13327.1 thousand, and total biomass of sturgeons was estimated at about 295.0 tons. In the Autumn 2012 total abundance was estimated 14364.9 thousand, and total biomass of sturgeons was estimated at about 271.0 tons.
Data obtained from sturgeon catch including sturgeon catch figures and caviar harvested during 2009-2012 revealed that the catch figures diminished during these years. Acipenser persicus showed the highest catch abundance (61%) while Huso huso was the dominant species caught in beach seine by weight. Acipenser persicus had a significant share in the caviar harvested during 2009 to 2012 and a total of 60.5, 52.6, 50.3 and 53.3% of caviar were harvested from this species in 2009, 2010, 2011 and 2012, respectively.
CPUE for all sturgeon species declined to 34.3% in sturgeon catch stations and to 44.15 % in beach seine from 2012 to 2009.
The highest CPUE (relative density) was recorded in region 4 in 2012 following by region 5, 3, 1 and 2. The highest CPUE for Huso huso and Acipenser nudiventris were recorded in region 4 and 5, respectively. Acipenser guldenstaedti showed the highest CPUE in central and northern regions while the highest CPUE for Acipenser stellatus was recorded in the western region. Except for Huso huso, mean weight and length of different sturgeon species showed decreasing trends during 2009 to 2012.
Females were dominant in all sturgeon species, while male Acipenser persicus was the dominant species caught in beach seine.
Most of the caviar harvested was first grade caviar while the percentage of second grade caviar caught in both catch stations and beach seine was higher than other grades in September. The mean weight of sturgeon caught in fishing traps was higher than those caught in beach seine. The mean weights of females were significantly higher than males. The percentage of weight of caviar to body weight in mature females was 17.2% in Acipenser stellatus, 21.8% in Acipenser persicus, 24.4% in Acipenser guldenstaedti , 24.1% in Acipenser nudiventris and 23.6 in Huso huso. Due to the sharp decline in natural and artificial breeding of sturgeon in recent years as well as decrease in number of suitable spawners and lack of proper conservation programs for sturgeon stocks, the sturgeon population will continue to decline in the following years and will reach its lowest level over the next decade. Therefore implementing a comprehensive study on conservation of sturgeon resources in order to decrease illegal catch, provide proper conditions for natural and artificial breeding programs, as well as fingerling release and strengthen administrative cooperation and research among all littoral countries is imperative to preserve and restore the valuable sturgeon stocks in the Caspian Sea.
The aligned mtDNA sequences of D-loop and cytochrom b genes were consisted of 500 and 700 base pairs (bp) respectively. 13 and 4 haplotypes were defined, the average haplotype diversity were 0.961 and 0.419, average nucleotide diversity were 0.038 and 0.002, The gamma distribution shape parameter were 0.19 and 0.20 indicating moderate mutation rate heterogeneity among sites in A.persicus. The lowest value of Fst for D-loop gene was calculated between Sefidrud and four fisheries region (-0.002) and the Fst values observed for cytochrom b gene was 0.04 with Nm=5.37 and not statistically significant. The exact test of population differentiation (non-differentiation exact P values) showed significant differences between Sefidrud and other areas (P ≤0.05) for D-loop gene and for cytochrom b gene was nonsignificant (P ≥0.05). The mismatch analysis produced a unimodal distribution of pairwise differences for both genes which was consistent with the sudden population expansion model. Tajima’s D and Fu’s Fs statistics were significantly negative (D= -0.84 and -0.99, P>0.01; Fs= -0.220 and -0.079, >0.01). ARLEQUIN calculated the value of t as 13.65 and the time since population expansion was estimated to be approximately 1501 years before present based on the mutation rates for the control region and this value for cytochrom b gene t= 0.98 which population expansion time was 7.84 years before present.
The results of this study based on D-loop gene showed that population of A.persicus in the Sefidrud River is differ from other studied areas. Therefore fisheries managements of this unique and valuable stock for restocking and conservation of gene pools is strongly recommended.
Histological results of gonads in A. persicus showed that 70.2 and 29.8 % of them were females and males, respectively. Sexually, 81, 15.5, 2.4 and 1.1 % of them were at stage I, II, III and IV of sexual maturation, respectively. Histological results in A. stellatus showed that 57.1 and 42.9 % of them were females and males, respectively. Sexually, 71.4 and 28.6 of them were at stage I and II, respectively. All of captured Acipenser nudiventris were females and 2 were at stage I and 2 were at stage II, sexually. Differential count results of blood leukocyte showed that the mean percent of lymphocyte, monocyte, neutrophile and eozynophile in Acipenser persicus were 79.5, 2.6, 8.2 and 9.7 %; in A.stellatus were 80.8, 3.1, 7.8 and 8.3 % and in Acipenser nudiventris and were 72.6, 3.2, 9.8 and 14.4 %, respectively. Results showed that there was not any significant difference in leukocytes numbers and the most and the least abundance belonged to lymphocyte and monocyte cells, respectively. Biochemical and ionic indices results showed that in Acipenser persicus, A.stellatus and A.nudiventris: cholesterol levels were 127.12, 69.88 and 69.4 mg/dl; total protein levels were 2.5, 1.87 and 2.78 g/dl; albumin levels were 1.04, 1.1 and 0.93 g/dl; magnesium levels were 5.7, 11.08 and 2.86 mg/dl; calcium levels were 14, 15.3 and 10.8 mg/dl; phosphor levels were 17.45, 17.6 and 18.5 mg/dl; sodium levels were 139.58, 136.95 and 139.6 meq/l; potassium levels were 5.3, 6.03 and 4.18 meq/dl; AST levels were 42, 18.7 and 15.2 µl; ALT levels were 1.45, 1.03 and 0.75 µl; IgM levels were 32.5, 22.6 and 32 mg/dl; Osmolarity levels were 346.6, 340.3 and 340.6 mOsmol/l, respectively. Therefore, based on obtained results, sturgeon was juvenile (1 – 2 - years), sexually and hematologically was juvenile and observed imbalance in their sexual.
