Population Dynamics Of Some Important Fish Species From Pakistani Waters

This study has estimated the growth and mortality parameters of some important fish species including Croaker Atrobucca alcocki, Tiger toothed croaker Otolithes cuvieri, and Ribbon fish Lepturacanthus savala using the length-frequency data in Pakistani waters. However the length-weight relationship (LWR), biological reference points (BRPs) were also estimated. The length-frequency data were collected from the fishery resources survey of Pakistan during the year 2009-2010. The Maximum sustainable yield were also estimated of Barramundi, Lates calcarifer and Black Pomfret Parastromateus niger using the catch and effort data taken from the fisheries statistics book of Pakistan complied by Marine Fisheries Department (MFD) Government of Pakistan, Karachi.Atrobucca alcockiThe fisheries statistics book of Pakistan is evident that prior to the fishery resources survey of Pakistan during the year 2009-2010, the Atrobucca alcocki were not observed in that abundance as observed in surveys during 2009-2010. The species was observed in a uniform abundance during the four demersal trawl surveys and it was the main objective of our study to estimate the growth and mortality parameters of this specie. In this connection a total of 819 (n= 819) length weight and 7240 (n=7240) length frequency of Atrobucca alcocki were observed, the minimum length were 10cm and maximum length were 44cm with the dominant length group ranges from 19 to 29cm. The total weight ranges from 14 to 928g. The length-weight relationship parameters were estimated as a= 0.012, b= 2.925 and R2= 0.972. Applying FiSAT computer software package using ELEFAN method the length-frequency distribution data were analyzed. The calculated von Bertalanffy growth function parameters were L∞= 47.25cm, K= 0.180 yr-1. Total mortality (Z) were computed using the length-converted catch curve analysis at Z=1.07yr-1. Natural mortality using Pauly’s equation were computed as M=0.494 yr-1 at an annual average sea surface temperature of 26℃, hence the fishing mortality were computed as F=Z-M= 0.576 yr-1.Yield per recruit analysis revealed that when tc was assumed to be 2,Fmax was calculated at 0.75 and F0.1 at 0.6. When tc was assumed to be 1,Fmax was calculated at 0.55 and F0.1 at 0.45. Current age at first capture is about 1 year and Fcurrent was 0.576 therefore Fcurrent was larger than F0.1 and Fmax, which shows that the fishery of Atrohucca alcocki may not be in a sustainable state in the region. Hence it is recommended that fishing effort may be reduced for the rational exploitation of the species in the region.Otolithes cuvieriAlthough 66 genera and 284 species belonging to the family Sciaenidae are distributed worldwide but in Pakistani waters 18 species belongs to family Sciaenidae are well known, but the catch in such abundance of Otolithes cuvieri were observed first time during the fisheries resources survey of Pakistani waters during the year 2009-2010. Keeping this in view we had put an attempt to estimate the growth and mortality parameters of the Otolithes cuvieri using the length-frequency data. Four demersal trawl surveys were carried out in Pakistani marine waters for the collection of length-frequency data of the species. The data used in present study for the combined sexes of the species were based on 3219 length-frequency (n=3219) and 671 length-weight (n=671) pairs. The length ranges from 3-35cm and weight ranges from1-208g. The dominant length of Otolithes cuvieri ranges from 4-18cm. The length weight relationship parameters were computed as a= 0.014, b= 2.870 and R2= 0.952. Using the ELEFAN routine of the FiSAT computer package, the calculated von Bertalanffy growth function parameters were L∞= 36.75cm, K= 0.300 year-1.Total mortality rate (Z) were computed using length-converted catch curve analysis at Z=1.26 year-Following the Pauly’s equation natural mortality rate were computed as M=0.740 year-1, at an average sea surface temperature of 26℃, fishing mortality rate were computed as F=Z-M= 0.52 year-1. The yield per recruit analysis showed that when tc was 1, Fmax was calculated at 0.5 and F0.1 at 0.4. When biological reference point of Fopt was M (0.740), current fishing mortality rate of 0.52 is smaller than the target biological reference point. This indicates that the fishery is in a safe condition.Lepturacanthus savalaLepturacanthus savala (Cuvier,1829) is a commercial fish species distributed in the coastal waters of Indo-west Pacific and Indian Ocean. In present study Length-frequency data were analyzed. The length-frequency data of Lepturacanthus savala (Cuvier 1829) were collected by the four demersal trawl surveys in the Pakistani waters in 2009-2010. A total of 4035 pairs of lengths and 1391 pairs of length-weight were measured. The length ranges from 1 to 121cm with average length of 44.23cm (± 19.75cm) while weight ranges from 1 to 1942g with average weight of 110.81 g (±229.57g). The estimated values of length-weight relationship for L. savala were W= 0.0001* L?.191(R2=0.960).The calculated von Bertalanffy growth function parameters using ELEFAN method in FiSAT computer package of L. savala were L∞= 133.35cm and k= 0.130year-1,t0 were estimated at -0.877. The estimated rate of total mortality Z applying the length-converted catch curve analysis method for L. savala was Z=0.49year-1, natural mortality M were estimated as M=0.304 year-1 at an annual average sea surface temperature of26℃ while the rates of fishing mortality F was calculated as F= 0.185year-1. Hence exploitation ratio (E=F/Z) were calculated as 0.377 yr-1. Yield per recruit contour map reveals that when tc was assumed to be 1, Fmax was estimated at 0.6 and F01 at 0.45. Current age at first capture was about 1 year and Fcurrent was 0.185 therefore Kcurrent was smaller than F0 1 and Fmax.When biological reference point Fopt was equal to M (0.304), current fishing mortality rate of 0.185 is smaller than the target biological reference point. The estimated values of growth performance index for the L. savala from Pakistani waters wereφ=3.364 year-1. The estimated value of MSY was 26983t with the estimated biomass of 110135t. Again the obtained results of maximum sustainable yield (MSY) of 26983t for L. savala from Pakistani waters were larger than recent catch of 20375t; therefore we may indicate that the L. savala fishery in Pakistani may be in a sustainable state.hates calcarifer (MSY)This chapter was to estimate the maximum sustainable yield of the Barramundi Lates calcarifer because it is a commercially important fish species and was fished in abundance in 1980s from the southern part of the Indus delta but in recent years it is caught not in that abundance as in 1980s. Maximum Sustainable Yield (MSY) of Barramundi Lates calcarifer (Bloch,1790) fishery of Pakistan were estimated based on catch and effort data from 1995-2009. Two computer software packages CEDA (catch effort data analysis) and ASPIC (a surplus production model incorporating covariates) were applied. Three surplus production models including Fox, Schaefer and Pell-Tomlinson with three error assumptions of normal, log-normal and gamma were used by applying CEDA and two surplus production models including Fox and Schaefer were used by applying ASPIC computer software package. In CEDA initial proportion (IP) was used ranging from 0.1-09. The obtained MSY results using IP 0.8 (because the initial catch was roughly 80% of the maximum catch) in normal, log-normal and gamma error assumptions from Fox, Schaefer and Pella-Tomlinson models were about 107-117t (± 8.131-15.260)t and estimated R2 for three models with three error assumptions were about 0.61-0.67.The estimated MSY results of Fox and Schaefer models using ASPIC computer software package were 118t (±10.856)t and 109t (± 10.384)t and estimated R2 for Fox and Schaefer models were 0.803 and 0.794 respectively. The estimated values of MSY are smaller than the recent catch which indicates that the fishery of L. calcarifer in Pakistani waters is over-exploited. Hence it is recommended to the fishery managers that for the sustainable exploitation of the species in Pakistani waters fishing effort should be reduced.Parastromateus niger (MSY)Parastromateus niger is among the most important commercial fish species in the Pakistan. The main emphasis of this chapter was to evaluate the MSY maximum sustainable yield of Parastromateus niger fishery based on the catch and effort data from 1992-2009. The computer software package CEDA (catch effort data analysis) was used to analyze the catch and effort data for the estimation of maximum sustainable yield (MSY) of Parastromateus niger fishery from Pakistani waters. An initial proportion IP of 0.4 (because the initial catch was roughly 40% of the maximum catch) were applied, the estimated maximum sustainable yield (MSY) were about 2000-2300t, the correlation coefficient R2 were about 0.20-0.31. Gamma error assumption often showed minimization failure. The estimated MSY from CEDA is smaller than most recent catch of the data which indicates that the fishery of Black Pomfret P niger in Pakistani waters may not be in a sustainable condition. Hence it is suggested that, for the well being and sustainable utilization of the fishery, the fishery management authorities and other stack holder may take some necessary actions to ensure the sustainable exploitation of the species in the region for coming generations.