Caspian J. Env. Sci. 2011, Vol. 9 No.2 pp. 159~167 ©Copyright by The University of Guilan, Printed in I.R. Iran CJES [Research] Caspian Journal of Environmental Sciences Age, growth and mortality of the Persian Sturgeon, Acipenser persicus, in the Iranian waters of the Caspian Sea S. Bakhshalizadeh*1, A. Bani 1, S. Abdolmalaki2, R. Nahrevar2, R. Rastin2 1- Dept. of Fisheries, Faculty of Natural Resources, University of Guilan, P.O.Box 1144, Someh Sara, Iran 2- Inland water Aquaculture Research Institute, P.O.Box 66, Bandar Anzali, Iran * Corresponding author’s E-mail: [email protected] ABSTRACT The age and growth of the Persian Sturgeon, Acipenser persicus, obtained from the Iranian coastal waters of the Caspian Sea, were studied through analysis of the pectoral fin ray section from 180 specimens, ranging in fork length (FL) from 66 to 203 cm. The specimens were obtained from commercial fisheries between October 2008 and June 2010. Interpretation of growth bands in the pectoral fin ray sections was carried out objectively using the direct reading of thin sections and image analysis. The maximum age recorded in this study for the spacimens of Persian Sturgeon was 39 years. The von Bertalanffy growth parameters estimated for females were greater than for males. The estimates of asymptotic length (L∞) and growth -1 coefficient (K) of females were 173.07 cm and 0.1 year , respectively and for males 164.33 cm L∞ and 0.08 year -1 K respectively,. Total mortality coefficient (Z) for females and males was estimated to be 0.45 and 0.76 year -1, respectively. This study revealed differences in life history parameters of the Persian Sturgeon compared with those of previous studies, which may be associated with the current increased fishing pressure and degradation of environmental conditions. Keywords: Life history, Age, Growth, Longevity, Mortality, Persian Sturgeon, Caspian Sea. INTRODUCTION (such as accumulation of pollutants in The Persian Sturgeon, Acipenser persicus, is sediments, the damming of rivers, and the the most common of sturgeon species in the restriction water flows), have negatively Caspian Sea and the Volga, Kura, and Ural influenced the migration and reproduction rivers, and to a smaller degree in the Terek, of these fish (Birstein et al. 1997; Billard & Suli and Tamur Rivers. A small group of Lecointre 2001). Their stocks have been individuals live in the Iranian rivers, Sefid- reduced as have some other marine and Rud and Gorgan-chaii (Billard & Lecointre freshwater fish species worldwide (Myers & 2001). This species is the most common and Worm 2003; Pauly et al 2003; Safina et al. important sturgeon in landings from the 2005). Quantifying the nature and magnit- Iranian coastal waters of the Caspian Sea, ude of the differences in life history param- comprising more than 60% of total catch of eters of the Persian Sturgeon, as an example sturgeon (Moghim 2003). However, report of a species that is under fishing pressure, of sturgeon stocks in trawl surveys show warrants further investigation into the age that landings have sharply decreased from structure and mortality rates. The late age at 144.4 million individuals in 1976 to fewer maturity and 3 years spawning interval in than 38.79 million in 2005, as was confirmed the Persian Sturgeon probably inhibits by the Russsian Kaspernikh Institute population recovery (Pikitch et al 2005). The (Pourkazemi 2006). The Persian Sturgeon is population of the Persian Sturgeon is a highly valuable species, a long-lived fish expected to be sensitive to biases in that grows and matures slowly with a low estimation of life history traits (Brennan & rate of natural mortality (Billard & Lecointre Cailliet 1989). 2001). These characteristics coupled with Age estimation of the sturgeon is comm- high and unregulated commercial fishing, only made from cross sections of pectoral habitat loss and environmental degradation fin rays (Koch et al 2008). These Online version is available on http://research.guilan.ac.ir/cjes 160 Age, growth and mortality of the Persian Sturgeon bony structures provide the greatest meshes) in length by 2.7 m (18 meshes) in precision for the measurer and unlike other depth, with a mesh size (knot to knot) of structures such as opercles, clavicles, 150 mm. cleithra, and medial nuchals, they can be Gutted weight (W) to the nearest kilogram, collected without killing the fish (Brennan total length (TL) and fork length (FL) to the & Cailliet 1989). Pectoral fin sections of the nearest centimeter were recorded after Persian Sturgeon fulfill the requirements sacrificing all samples. Fish were sexed by for the measurement of aging in terms of macroscopic examination of the gonad. ease of collection, processing, legibility and The gender of three fish could not be precision of interpretation (Brennan & determined and therefore they were Cailliet 1989; Stevenson & Secor 2000). classified as immature. The right pectoral The objectives of this study were to explore fin rays were removed by hack saw for the the somatic growth, age structure and purpose of age analysis. mortality of the Persian Sturgeon in 2008- 2010 in order to determine whether changes Processing of pectoral fin ray in their life history parameters have The fin rays were placed in warm water for occurred owing to recent fishing mortality. 10 min (Jearld 1992) to separate soft tissues. They were then defleshed with a stiff brush Materials and methods and placed on filter paper to dry. Study sites and sampling Transverse sections were obtained using a A total of 151 of the Persian Sturgeon, fret saw and polished with 250 and 400 grit Acipenser persicus, were obtained from the sandpaper successively until a thickness of Iranian coastal waters of the Caspian Sea 0.3-0.6 mm was achieved. Samples were between October 2008 and June 2010 (Fig. cemented to a glass slide to keep them 1). Forty eight samples were obtained from immobilized. Glycerol was used to enhance commercial catches (for restocking the differentiation between the rings and to program) of the Iranian fisheries, using aid in the examination of growth increment anchored gill nets. Additionally, one formation under transmitted light using a hundred specimens were obtained from microscope system and a camera (Motic beach sein fisheries in order to provide a China Group Company) that displayed the broader range of fish. The gill nets used to image on a video monitor. The final collect samples measured 18 m (120 magnification used varied from 10 - 40 x. Fig 1. Location of sampling areas (white closed circles) of Persian Sturgeon in the Iranian coastal water of the Caspian Sea Bakhshalizadeh et al., 161 Bias and precision analyses Growth estimates and curves All sections were read twice by the first The length and weight of the Persian reader (the first author) and 11% of the Sturgeon estimated in this study were samples were randomly chosen for a compared with the mean length and weight second reading (by the fourth author) to obtained from a previous study (Taghavi determine the percentage agreement (PA). 1996) in the south Caspian Sea, using the All sections were read blindly without Student΄s one sample t-test (Zar 1996). reference to fish size. Age estimates were Linear, logarithmic, power, Von Bertalanffy, accepted if counts were identical between and exponential equations were tested to readings. If counts differed by 1 year, fish acquire the best fit of size-at-age data. were allocated the higher age on the basis Finally, growth was characterized using von of conservative assumption that a reader Bertalanffy growth function, fitting to size- was more likely to underestimate age by at-age data using standard nonlinear overlooking a partly obscured section than optimization methods. The von Bertalanffy to overestimate age by counting an growth function is explained as: -K (t-t ) anomaly like false bands (Brennan & Lt = L∞ (1- e 0 ) Cailliet 1989). If counts differed by 2 years where Lt is length at age t, L∞ is the or more, sections were read again until asymptotic length, K is the growth coefficient agreement was within one year. and t0 is the hypothetical age at which length To assess the precision of ring counts of the is equal to 0. The comparison of von fin ray sections provided using images, the Bertalanffy growth curves of the gender was ages of the total 148 samples were done using an analysis of the residual sum of estimated by the first reader, from one squares (ARSS) (Chen et al. 1992). section provided using both the direct Parameters of the length-weight reading and estimates from the images. relationship were achieved by fitting the The average percent error (APE) between power function to length and weight data the ring counts using the two techniques (Ricker 1975): was calculated using the following formula W = a FLb (Beamish & Fournier 1981): where W is the gutted weight, a and b is a 100 N 1 R Xij − Xj regression constant and FL is the fork APE = length. Condition factor (KF) was N ∑∑R Xj j==11 i calculated by KF=W/a FLb and the where N is the number of fish aged in the comparison of KF between the genders was sub sample, R is the number of times the performed by applying the ANOVA test age of each fish were estimated, Xij is the (Saberowski & Buchholz 1990). ith determination for the jth fish, and Xj is the average estimated age of the jth fish. A Mortality paired sample T-test was used to determine To estimate annual instantaneous rate of if there was a difference between the ages total mortality coefficient (Z) we used the estimated using the two techniques. formula (Gulland, 1983): In addition, the precision of age estimates − K ( L − L ) was also assessed between two readers by Z = ∞ the coefficient of variation (CV) as indices − ( L − L ′) of precision (Chang 1982).