Iranian Journal of Fisheries Sciences 11(1) 48-62 2012 Growth parameters, mortality rates, yield per recruit, biomass, and MSY of Rutilus frisii kutum, using length frequency analysis in the Southern parts of the Caspian Sea 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 fish 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 animals 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 fishes 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.