Iranian Journal of Fisheries Sciences 11(1) 48-62 2012

Growth parameters, mortality rates, yield per recruit, biomass, and MSY of frisii kutum, using length frequency analysis in the Southern parts of the

Gheshlaghi P.1; Vahabnezhad A.2; Taghavi Motlagh S. A.2

Received: March 2011 Accepted: July 2011

Abstract The growth and mortality coefficient of Rutilus frisii kutum, were estimated using length frequency data collected in southern waters of the Caspian Sea during October 2008 to April 2009. The following population parameters were evaluated: length-weight relationship, W = 3.258 0.004L , (r= 0.976); Von Bertalanffy growth constants, W∞ (g) = 4192.3, L∞ (cm) =

70.45, K = 0.2, per year; t0 = −0.75; total mortality and its components, Z = 0.92, M = 0.36, F = 0.56 per year. The exploitation rate (E) was estimated about 0.6. The current yield per- recruit was estimated to be 279.15 g, which was only 1.2% less than Maximum yield per

recruitment that was estimated as YPRmax = 287.535, it means if fishing mortality increases from 0.56 per year to 0.7 per year, the yield will raise by only 1.2%. The current YPR and maximum YPR, which were gained at fishing mortality of 0.7, showed that most kutum individuals are caught before reaching the length of maturity. Therefore, to get a maximum YPR, it is necessary to increase fishing effort, even higher than the optimum level. Keeping Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 kutum fishing at the current level will permit harvest of the sustainable yield and avoid overfishing problems.

Keywords: Biomass, Caspian Sea, mortality, Rutilus frisii kutum, Exploitation rate

______1-Department of fisheries, Sciences and Reasearch, Islamic Azad University, Tehran, Iran. 2-Iranian Fisheries Research Organization, IFRO. P.O. Box: 14155- 6116. Tehran – Iran. * Corresponding author's email: [email protected] 49 Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

Introduction Yield per recruit models examine the fisheries in southern waters of the Caspian trade-off between capturing a large Sea (Iranian Fisheries Organization number of early in their life span and statistical year book, 2009) and it makes capturing a smaller number of larger fish up to 60% of yearly fishermen income. In later in their life span (King, 1995). The this study, the length frequency data of R. classical Beverton and Holt (1957) yield frisii kutum gained from commercial per recruit model considers the catches in the Southern Caspian Sea dependence of yield upon growth, age at (Iranian side) were used to estimate first capture, and fishing mortality. population parameters, yield per recruit, Length-based cohort analysis was biomass and MSY for sustainable developed for species that cannot be aged. exploitation. This information is necessary The principle is the same for age-cohort to formulate management and analysis, but are separated into conservation policies as well as fishery length classes (Jones, 1981). A virtual development for this species in the population denotes the exploited Southern Caspian Sea in future. population, and the analysis estimates the population that must have been present to produce the catch. From the observations Materials and methods on the number caught in each age/length Length-frequency data of R. frisii kutum group and from independent estimates of was collected from October 2008 through the natural mortality, the VPA estimates April 2009 from the Beach Seine how many fish there must have been in the cooperative fishing, along the southern sea to account for that catch (Prakarn, part of the Caspian Sea (Iranian side). The 2002). trade catches of bony fish is commenced at A morphometric study over the this time of the year. From May to Rutilus frisii kutum was conducted in some September, catch of bony are Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 selected rivers located in sothern Caspean forbidden. A total of 16517 specimens of Sea (Abdolhay et al., 2010), last years. R. R. frisii kutum were collected. Fork length frisii kutum is a valuable commercial fish was measured to the nearest cm and the in the southern part of the Caspian Sea and weight was measured to the nearest g, both has a great demand, due to its good taste presented accompanying with ±SD. and culinary customs of the local people. Length and weight were pooled from Its stocks declined mainly due to different beach seines by month and deterioration of habitats, natural spawning grouped into 1 cm length groups. The ground, illegal catch and overfishing FISAT II was applied for data analysis (Kavan et al., 2009). In the IUCN Red list (Gayanilo and Pauly, 1997). published in 2000, this species has been The length-weight relationships were listed as Data Deficient species (Taylor estimated from the formula, and Mittermeier, 2000). This species Where: constitutes about 50% of the annual catch W is total body weight (g), L is the fork of the bony fishes from Beach Seine length (cm), a and b are coefficients of the Iranian Journal of Fisheries Sciences, 11(1), 2012 50

functional regression between W and L equation for growth in length were (Ricker, 1973). estimated by means of ELEFAN-I (Pauly and David, 1981, Saeger and Gayanilo,

Asymptotic length (L∞) and growth co- 1986). The t0 value estimated using the efficient (K) of the von Bertalanffy empirical equation: (Pauly, 1979) The growth performance of R. frisii kutum Total mortality (Z) was estimated using population in terms of length was length converted catch curve method as compared as: implemented in ELEFAN II. Natural (Pauly and mortality rate (M) was estimated using Munro, 1984) Pauly’s empirical relationship:

Maximum age (tmax) was estimated as:

(Pauly, 1983) (Pauly, 1980) Where: L∞ is expressed in cm and T, the mean The length-based cohort analysis (VPA) annual environmental temperature in °C by Jones (1984) is applied to estimate which is 14°C for the Caspian Sea stock sizes of R. frisii kutum in the (Abdolmalaki and Ghaninejad, 2008). Southern Caspian Sea. The values of L∞, Fishing mortality (F) was obtained by K, M, F, a (constant) and b (exponent) for subtracting M from Z and exploitation rate the species were used as inputs to a VPA (E) was estimated from (Gulland, 1971). analysis (Table 1). Table1: The length-based cohort analysis (VPA) by Jones (1984) for calculation of biomass Column Contents Column Contents

Catch C(Lt ,Lt+1) Exploitation Rate Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021

XL (Where L t Total Mortality lower boundary of the tail length class t)

; Number of Number at Sea Survivors (Nt)

Biomass (Kg) Survival Factor

The maximum sustainable yield (MSY) for analysis in the same year and M is the R. frisii kutum was also estimated, using natural mortality. Cadima’s formula: Recruitment length was estimated (Lr), the midpoint of the smallest length group in Where: the catch was taken as length at Y is the total catch in a year and B is recruitment (Murty et al., 1992). Relative average biomass calculated from cohort yield per recruit (Y/R) value as a function

51 Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

of F was determined from the estimated written in the form suggested by Gulland growth parameters and probability of (1979), and reviewed in Sparre et al. capture by length (Pauly and Soriano, (1989) was applied for calculating YPR, or 1986 cited in Maclean, Dizon and providing advice in terms of yield per Hosillos, 1986). The following Beverton recruit: and Holt (1957) yield per recruit model,

Where: and L∞ are parameters of the von Y/R is yield per recruit, F is the fishing Bertalanffy growth equation and Z is the mortality coefficient, M is the natural instantaneous mortality rate. mortality coefficient, tc is the mean age at Emax, E0.1 and E0.5 are estimated by using first capture, tr is the mean age at the first derivative of this function. Emax is recruitment, W∞ is the asymptotic weight, the exploitation rate at Maximum Z is total mortality, K is growth coefficient Sustainable Yield (MSY), E0.1 is the rate at and S can be estimated from: Length at Maximum Economic Yield (MEY) and first capture (Lc) was determined using the E0.5 is the optimum exploitation rate. equation of: (Beverton and Holt, Results Figure 1 indicated the annual catch of R. 1957) frisii kutum in the southern part of the Where: Caspian Sea (Iranian side) from 1996 to Lc is the length at first capture, L' is the 2007, which showed positive trends with mean length of fish in the catch sample, K R = 0.76. Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021

Figure 1: Annual catch of R. frisii kutum during 1996 -2007 in the southern Caspian Sea

For 16517 R. frisii kutum samples Sea over the study period was recorded as collected during 2008 to 2009, the fork 41.5±16.09. The weight of caught fishes length ranged 14 to 69 cm collected from (N= 551) varied between 190 to 2370 g fishery. Mean fork length ± SD of the R. with the average of 948.1±0.457g. Figure frisii kutum caught in the southern Caspian 2 showed length frequency distribution of Iranian Journal of Fisheries Sciences, 11(1), 2012 52

the catch for this species. The highest kutum in the Southern Caspian Sea was 40 frequency of catches belonged to the cm (Daryanabard et al., 2007), the length of class 39-40 cm and lowest proportion of fish in aggregated length belonged to 63-64 cm. As the legal size frequency samples that were below mean (standard length) for catching R. frissi standard size was calculated about 52.8 %.

Figure 2: Length frequency distribution of R. frisii kutum catches in the Southern Caspian Sea

The length- weight relationship provided a Graphic representation of the estimated good fit for R. frissi kutum data as, length weight relationships was given in W = 0.0049L 3.258, (r= 0.972). The b value Figure 3. was not statistically different from 3 (t- test; P>0.05),

Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021

Figure 3: Length-weight relationship of R. firisii kutum in the southern part of the Caspian Sea The K-scan technique indicated L∞ of equation for this species as: Lt = 70.45 70.45cm and k value of 0.2 per year. Age (1-exp (-0.2(t+0.75)) at Zero length was estimated as -0.75 year, The length –weight relationship was used which gave the Von Bertalanffy growth to convert the asymptotic length (L∞ =

53 Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

70.45 cm FL) to the corresponding was described by the following equation: 3 asymptotic weight (4192.3 g). The von Wt = 4192.3 (1 – exp (- 0.2 (t + 0.75))) Bertalanffy equation for growth in weight

Figure 4: The von Bertalanffy growth function fitted to size-at- age relationship for R. frisii kutum in the Southern Caspian Sea

The growth performance was estimated as length at first capture (Lc) was adopted as ´=2.9. R. frisii kutum attained their 29.8 cm and the corresponding age (tc) maximum size (K= 0.2 per year) and had a was 2 years. Figure 5 illustrated the yield -1 long life span of 14.25 years. The per recruit plot where Fmax= 0.7 year , as instantaneous total mortality coefficient the present level of fishing mortality is -1 (Z) was estimated from the length of F=Z-M= 0.56 year . converted catch curve as 0.92. The natural The Beverton and Holt relative mortality (M), fishing mortality (F) and yield per recruit model (Fig. 6) showed annual mortality (A) were estimated to be that the indices for sustainable yield were -1 0.36, 0.56 and 0.60 year respectively. The 0.278 for optimum sustainable yield (E0.5), Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 exploitation rate was estimated as E = 0.421 for the maximum sustainable yield 0.60. The survival rate was estimated to be (Emax) and 0.355 for economic yield target 0.39% after recruitment to the fishing (E0.1). The current exploitation rate was ground. Weight of fish in each length class estimated 0.6 gained from the analysis of and rate of total fishing were calculated by mortality rates, which was already above using growth and mortality parameters. the maximum, optimum and economic The biomass value of R. frisii kutum was yield indices. estimated to be 36124.34 tons (Table 2), The typical selectivity for R. frisii which provided the maximum sustainable kutum caught in the Beach Seine showed yield product (MSY) as 13652 tons. The that at least 25% of fish of 31.19 cm FL, midpoint of lower length classes in the 50% of the fish of 33.92 cm FL and 75% sampled data was used as a length at of all fish of 36.64 cm FL were retained by recruitment which is 14.5 cm and the the Beach Seine (Fig.7). correspondence age was tr= 1 years. The

Iranian Journal of Fisheries Sciences, 11(1), 2012 54

es n 1199348 792655 512169 316622 176385 50711 687473 1168058 1783802 2487730 3209630 3811707 4167405 4218318 3900564 3270922 2556874 1813968 Biomass Biomass (kg) Total Total Biomass: 36124.34 ton

21132736 20079147 18716570 16995449 15003310 12680446 10186699 7779421 5549399 3658917 2286030 1314946 713836 391707 212249 111023 52758 13034 Number at Number sea

0.88 0.75 0.68 0.55 0.53 0.47 0.38 0.38 0.48 0.51 0.61 0.69 0.79 0.83 0.98 0.96 0.99 1.01

Total mortality (Z)

3 0.04 0.05 0.25 0.29 0.41 0.48 0.54 0.57 0.63 0.6 0.64 0.64 0.59 0.52 0.47 0.34 0.32 0.23 Exploration rate

(S) 0.90 0.89 0.86 0.84 0.80 0.76 0.71 0.68 0.60 0.57 0.52 0.47 0.46 0.45 0.40 0.37 0.21 0.18

Survival Survival factor frisii kutum frisii R. R.

994

79320986 71381911 63782892 54783315 46106411 37013224 28217630 20162976 13701 8287509 4760096 2492581 1163738 535056 240100 96070 35295 7428 1351 Nt) Number of of Number survivors )

XL 1.05 1.05 1.06 1.06 1.07 1.07 1.08 1.09 1.10 1.11 1.12 1.14 1.17 1.21 1.27 1.38 1.66 1.89

16701 331290 370526 2261611 2558542 3691995 4230633 4387442 3660389 34 2210202 1444544 855462 371700 153941 67621 20806 8873 1384 837 Catch

ones’ length cohort analysis illustrated for J 0.3006 0.4091 0.5422 0.7029 0.8940 1.1185 1.3795 1.6801 2.0236 2.4131 2.8518 3.3433 3.8907 4.2885 0.0325 0.0582 0.0953 0.1464 0.2139 Weight Weight (kg)

0.07 0.15 1.45 2.52 5.32 8.57 12.10 13.38 16.19 13.32 10.89 7.96 4.21 2.10 1.10 0.40 0.20 0.04 0.02 Frequency (%)

30.5 33.5 36.5 39.5 42.5 45.5 48.5 51.5 54.5 57.5 60.5 63.5 66.5 68.5 15.5 18.5 21.5 24.5 27.5 Mid point

he calculation procedure of T :

17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 ------14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68

Table2

(cm) Length class

Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 6th October Wednesday on +0330 16:20 at jifro.ir from Downloaded 55 Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

Figure 5: Relative yield per recruit (Y/R) versus fishing mortality (F) for R. frisii kutum in the Southern Caspian Sea

Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 Figure 6: Beverton and Holt’s relative yield per recruit and average biomass per recruit models, showing levels of yield indices: EOPT -optimum yield, EMEY - maximum economic yield, EMSY – maximum sustainable yield and ECUR - current level of exploitation for R. frisii kutum in the Southern part of Caspian Sea.

Iranian Journal of Fisheries Sciences, 11(1), 2012 56

Figure 7: Logistic selection curve showing 25%, 50% and 75% selection length (cm FL) of R. frisii kutum (broken lines) from the southern Caspian Sea.

Discussion

Length based stock assessment showed an slowly (K= 0.2) and had a long life span of

asymptotic length (L∞) of 70.45 cm FL 14 years, thus a clear indication of poor

and growth curvature (K) of 0.2 year-1. growth of Kutum in the Southern Caspian

These values did not show much Sea.

difference when compared to the L∞ and In our study, maximum recorded

K values estimated by other authors (Table fork length and weight were 69 cm and

Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 3). In Iranian Coastal Waters of the 2370 g respectively, although maximum

Caspian Sea the value of asymptotic length lengths of 61cm and 71 cm have been

of R. frisii kutum ranged from 60 to 72 cm reported (Daryanabard et al., 2007) and

and has showed little difference with its (Muus and Dahlstrom, 1968). In contrast,

value in 1971, which is 63.2 cm Afraei et al. (2010) reported maximum (Abdolmaleki and Ghaninejad, 2000). The fork length and weight of 58 cm and 2450 asymptotic length of 70.45 cm estimated g for Kutum in the Southern Caspian Sea. for Kutum in this study was considerably Difference in length and weight can vary

greater than the maximum observed length with geographical location that is probably

of 63 cm and 58cm (FL) reported before in related to factors such as climate, trophic

2006-2008 (Afraei et al., 2010). status, diet and exploitation rates (Kohler

Kutum attained its maximum size and Hubert, 1999).

57 Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

Table3: Summary of the growth parameters estimated for R. frisii kutum Area Sex L∞ K Ø' Reference Bay of Astrabad F 113.7 0.09 3.04 Berg,1948-1949

Bay of Kura F 130.2 0.08 3.14

Malyi Kyzylagach Bay F 80.5 0.18 3.07 Abdorakhmanov, 1962

M 79.0 0.18 3.06

Anzali Lagoon F 80.4 0.20 3.12 Ralonde and Razavi, 1972

M 70.6 0.12 2.79

Anzali Lagoon F 104.2 0.09 3.02 Holcik and Olah, 1992

M 48.7 0.22 2.72

Former USSR F+M 62.2 0.40 3.2 Belyaeva et al., 1989

Southern Caspian Sea F+M 58.28 0.26 Daryanabard et al., 2007

Southern Caspian Sea F+M 63.0 0.21 2.89 Afraei et al. 2010

F 62.03 0.21 2.91

M 54.52 0.27 2.92

Southern Caspian Sea F+M 70.45 0.2 2.9 Present Study

*F= female, M= male, USSR= Union of Soviet Socialist Republic, L∞ = asymptotical length (cm), K= growth rate, and ǿ = growth performance Index

The estimated growth performance (Ø'= different from 3 (P>0.05), the parameters 2.9) showed best concurrence with value of length-weight relationship estimated in obtained by Afraei et al. (2010), also this the present study fall within the results of Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 value existed within the corresponding the previously reported values in other values in other localities (Table 3). localities (Table 4). The length-weight relationship of R. frisii kutum showed an isometric pattern, since the slop of model was not significantly

Table 4: Length- weight relationship of R. frisii kutum in the Southern Caspian Sea a b Locality References 0.004 3.258 Southern Caspian Sea Present paper - 3.02 Southern Caspian Sea Afraei et al, 2010 0.0101 3.073 Southern Caspian Sea Daryanabard et al., 2007 Terkos Dam, 0.0202 2.850 Tarkan et al., 2006 Marmara 0.0172 2.976 Southern Caspian Sea Belyaeva et al., 1989 - 2.30 to 5.50 Bagenal, 1978 * a and b are the coefficients of the functional regression between Weight and Length

Iranian Journal of Fisheries Sciences, 11(1), 2012 58

The total mortality (Z= 0.92 yr-1) value in standard length for capturing Kutum in this study was lower than the Z values Iranian waters is 40 cm, the results of estimated for the same species, which were logistic gear selection model indicated that 1.079 yr-1 (Daryanabard et al., 2007). The most Kutum individuals were caught natural mortality (M=0.36 yr-1) did not before they could reach standard length. show much difference as contrasted to the We present evidence from yield per recruit natural mortality (M) estimated for the models and logistic gear selection model same species which was 0.3 yr-1 that growth of overfishing of Kutum was (Daryanabard et al., 2007). unlikely under current fishing logistic gear The yield per recruit of R. frisii kutum selection model practices in this part of the (Fig. 6) increased rapidly as fishing Caspian Sea. The current exploitation rate mortality increased reaching a maximum of 0.6 for R. frisii kutum, derived from the value (MSY/R= 287.535) at the fishing analysis of mortality rates, was already mortality of F= 0.7. At the present value of above the maximum, optimum and fishing mortality (F= 0.56), age at first economic yield indices. Comparison of capture (Tc= 2Years) and natural mortality this value with 0.61 (Abdolmaleki et al., (M= 0.36 yr-1), the current YPR was 2007) and 0.62 (Ghaninejad et al., 2001), estimated to be 279.15 g, only 1.2% less put forward that Kutum was exploited than the maximum yield per recruit (YPR= optimally in the Southern Caspian Sea. 287.535). It means if fishing mortality The calculated stock biomass of R. frisii increased from 0.56 per year to 0.7 per kutum was 1300 tons in 1971 fluctuating year, the yield will increase by only 1.2%. between 18489 to 36124.34 tons, during The current YPR and maximum YPR 1990 to 2009 )Abdolmaleki, 2009). In which were gained at fishing mortality of recent years, total catch of this fish had 0.7 showed the most Kutum individuals greatly fluctuated due to the disruption of fished before they achieved standard size, the natural spawning grounds and over Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 therefore to get maximum YPR, it was fishing. The substantial reduction to 1.298 necessary to increase fishing effort even metric tons, the lowest total catch reported higher than the optimum level. The result in 1984–1985, could be due to over of YPR analysis indicated that although exploitation of the fishery resources. the current fishing mortality was not very However, the total catch has increased high, but most of the Kutum were caught after the fingerlings release programs by fishermen before reaching standard size started in 1979. The total numbers of R. result in losing economic advantage. frisii kutum released fingerlings increased Results obtained from the logistic gear from 12 million in 2002 to 187.1 in 2008. selection model suggested 25% of fish of The total catch also increased from 6417 31.19 cm FL, 50% of the fish of 33.92 cm metric tons to 14835 metric tons in years FL and 75% of all fish of 36.64 cm FL, a 2002 and 2008, respectively (Abdolhay et condition which can have serious al., 2010) . consequences on management of R. frisii The rate of increasing MSY during the kutum in the Southern Caspian Sea. As the years 1991-2009, noted that these trend

59 Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

changes were parallel with the trend of Reviews in Fish Biology and Fisheries. change in the total amount of kutum March 18. fishing (total legal and illegal fishing). Abdolhay, H., 1997. Artificial Keeping Kutum fishing at the present level reproduction of fish for stock will permit harvest of the sustainable yield enhancement in south of the Caspian and avoid overfishing problems. In Sea. Proceedings of the 7th conclusion, the yield per recruit model s Conference of Shilat, Responsible typically used for management of Fisheries. Iran. Tehran. Februry.1997. regulatory fishing mortality in order to Abdolmaleki, S. H. and Ghaninejad, D., obtain sustainable harvests from a stock. 2009. Stock Assessment of the Caspian These regulations have been historically kutum Rutilus frisii kutum in the resulted in harvests with large biomass that Iranian Coastal Waters of Caspian Sea. were valued in commercial fisheries. We Iranian Fisheries Scientific Journal, present evidence from yield per recruit 16, 113-16. (In Persian) models and logistic gear selection model Abdolmaleki, S. H., Hashemi, A. and that showed growth of overfishing of Nahror, R., 2007. Fishing status and kutum was unlikely under current fishing population structure of logistic gear selection model practices in Rutilus frisii kutum in the Iranian this part of the Caspian Sea. On the other Coastal Waters of Caspian Sea, hand in our analysis, we have revealed that Journal of Marine Science and fishing practices by harvesting under size Technology, 6(2), 51-62. fish have substantial impact s on the Abdolmaleki, S. H. and Ghaninejad, D., production of Kutum. 2000. Stock Assessment of the Caspian References kutum Rutilus frisii kutum in the

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V Gheshlaghi et al. Growth parameters, mortality, yield, biomass, and MSY of kutum,….

برآورد متغييرهاي رشد، نرخ مرگ و مير، توليد به ازاي احياء، زيست توده و

تحليل حداكثر طول قابل برداشت ماهي سفيد در جنوب درياي خسر

پگاه قشالقي1*؛ آرزو وهاب نصاد؛2 سيد امين ا.. تقوي مطلق2

چکيده ضاخصُاي ضرية رضذ ي مرگ ي ميرماَي سفيذ تا استفادٌ از دادٌ َاي طًل ماَي در جىًب درياي خسر از تاريخ مُر ماٌ 1388 تا مرداد ماٌ 1389 جمع آيري ضذٌ است. متغييرَاي زير در ارتثاط تا جمعيت ايه ماَي مًرد تررسي قرار گرفت. راتطٍ طًل تا 3.258 يزن عثارتست از ;(W = 0.004L , (r= 0.976، ضرية ثاتت رضذ ين ترتالىفي ,W∞(g) = 4192.3, (cm) = 70.45 ,L∞ K = 0.2 در سال، t0 = −0.75 ، ضرية مرگ ي مير كل ي اجساء آن Z = 0.92, M = 0.36, F = 0.56 در سال مي تاضذ. ورخ تُرٌ ترداري (E) حذيد 6/0 ترآيرد گرديذ. عملكرد فعلي تًليذ در صيذ 11/279 گرم ترآيرد ضذٌ كٍ فقط 2/1 درصذ كمتراز حذاكثرعملكرد صيذ ترداضت ضذٌ تخميه زدٌ ضذٌ ي عثارتست از YPRmax = 287.535 مي تاضذ كٍ تذيه مفًُم تًدٌ كٍ ميسان مرگ ي ميرصيذ ماَي سفيذ از 16/0 در سال تٍ 7/0 در سال افسايص يافتٍ است ي عملكرد تًليذ 2/1 درصذ افسايص مي ياتذ. تىاتر ايه ضرية YPR در حال حاضر ي ضرية حذاكثر YPR تٍ 7/0 در َر سال خًاَذ رسيذ ي در اكثر مًارد ايه ضرية وطان ميذَذ كٍ صيذ ماَي سفيذ قثل از رسيذن تٍ طًل ماَي درسه تلًغ تًدٌ است. تىا ترايه جُت رسيذن تٍ حذاكثر ضرية YPR، وياز تٍ تالش تيطتر در صيذ حتي تيطتر از سطح مطلًب خًاَذ تًد. حفظ ميسان سطح ترداضت ماَي سفيذ ي جلًگيري از صيذ تي رييٍ تٍ عىًان مطكالت فعلي مي تاضىذ.

Downloaded from jifro.ir at 16:20 +0330 on Wednesday October 6th 2021 واشگان كليدي: زيست تًدٌ، درياي خسر، مرگ ي مير، ماَي سفيذ ، ورخ ترداضت

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1- دانشگبه آزاد اسالمی، واحد علىم و تحقیقبت تهران، گروه شیالت، تهران، ایران. 2- مىسسو تحقیقبت شیالت ایران، تهران، ایران. صندوق پستی 6116 – 15111 *پست الکترونیکی نىیسنده مسئىل: [email protected]