The instantaneous total mortality rate(Z) of a fish population is one of the important parameters in fisheries stock assessment. The estimation of Z is crucial to fish population dynamics analysis,abundance and catch ...The instantaneous total mortality rate(Z) of a fish population is one of the important parameters in fisheries stock assessment. The estimation of Z is crucial to fish population dynamics analysis,abundance and catch forecast,and fisheries management. A catch curve-based method for estimating time-based Z and its change trend from catch per unit effort(CPUE) data of multiple cohorts is developed. Unlike the traditional catch-curve method,the method developed here does not need the assumption of constant Z throughout the time,but the Z values in n continuous years are assumed constant,and then the Z values in different n continuous years are estimated using the age-based CPUE data within these years. The results of the simulation analyses show that the trends of the estimated time-based Z are consistent with the trends of the true Z,and the estimated rates of change from this approach are close to the true change rates(the relative differences between the change rates of the estimated Z and the true Z are smaller than 10%). Variations of both Z and recruitment can affect the estimates of Z value and the trend of Z. The most appropriate value of n can be different given the effects of different factors. Therefore,the appropriate value of n for different fisheries should be determined through a simulation analysis as we demonstrated in this study. Further analyses suggested that selectivity and age estimation are also two factors that can affect the estimated Z values if there is error in either of them,but the estimated change rates of Z are still close to the true change rates. We also applied this approach to the Atlantic cod(G adus morhua) fishery of eastern Newfoundland and Labrador from 1983 to 1997,and obtained reasonable estimates of time-based Z.展开更多
The objective of this study was to estimate natural, fishing and total mortality, survival and exploitation rates of Clupeonella engrauliformis in the southern Caspian Sea. Survival rate and natural mortality were cal...The objective of this study was to estimate natural, fishing and total mortality, survival and exploitation rates of Clupeonella engrauliformis in the southern Caspian Sea. Survival rate and natural mortality were calculated using catch curve and Pauly methods, respectively. Natural and fishing mortality have been estimated up to 0.633 yr^-1 and 0.437 yr^-1, respectively. According to catch curve method, the annual survival rate of anchovy kilka has been estimated up to 0.343 yr^-1. With owning this survival rate, the instantaneous coefficient of total mortality of anchovy kilka has been estimated up to 1.07 yr^-1. The exploitation rate of anchovy kilka has been estimated up to 0.408. The catch amounts of anchovy kilka decreased gradually mainly due to overfishing, predators and ecological disturbances occurred in the Caspian Sea. The results suggest that the population of anchovy kilka were overexploited in the past years and were vulnerable to their natural predators.展开更多
基金Supported by the USDA Cooperative State Research,Education and Extension Service,Hatch Project(No.0210510)the National Natural Science Foundations of China(Nos.31270527,40801225)+1 种基金the Natural Science Foundation of Zhejiang Province(No.LY13D010005)the Young Academic Leaders Climbing Program of Zhejiang Province(No.pd2013222)
文摘The instantaneous total mortality rate(Z) of a fish population is one of the important parameters in fisheries stock assessment. The estimation of Z is crucial to fish population dynamics analysis,abundance and catch forecast,and fisheries management. A catch curve-based method for estimating time-based Z and its change trend from catch per unit effort(CPUE) data of multiple cohorts is developed. Unlike the traditional catch-curve method,the method developed here does not need the assumption of constant Z throughout the time,but the Z values in n continuous years are assumed constant,and then the Z values in different n continuous years are estimated using the age-based CPUE data within these years. The results of the simulation analyses show that the trends of the estimated time-based Z are consistent with the trends of the true Z,and the estimated rates of change from this approach are close to the true change rates(the relative differences between the change rates of the estimated Z and the true Z are smaller than 10%). Variations of both Z and recruitment can affect the estimates of Z value and the trend of Z. The most appropriate value of n can be different given the effects of different factors. Therefore,the appropriate value of n for different fisheries should be determined through a simulation analysis as we demonstrated in this study. Further analyses suggested that selectivity and age estimation are also two factors that can affect the estimated Z values if there is error in either of them,but the estimated change rates of Z are still close to the true change rates. We also applied this approach to the Atlantic cod(G adus morhua) fishery of eastern Newfoundland and Labrador from 1983 to 1997,and obtained reasonable estimates of time-based Z.
文摘The objective of this study was to estimate natural, fishing and total mortality, survival and exploitation rates of Clupeonella engrauliformis in the southern Caspian Sea. Survival rate and natural mortality were calculated using catch curve and Pauly methods, respectively. Natural and fishing mortality have been estimated up to 0.633 yr^-1 and 0.437 yr^-1, respectively. According to catch curve method, the annual survival rate of anchovy kilka has been estimated up to 0.343 yr^-1. With owning this survival rate, the instantaneous coefficient of total mortality of anchovy kilka has been estimated up to 1.07 yr^-1. The exploitation rate of anchovy kilka has been estimated up to 0.408. The catch amounts of anchovy kilka decreased gradually mainly due to overfishing, predators and ecological disturbances occurred in the Caspian Sea. The results suggest that the population of anchovy kilka were overexploited in the past years and were vulnerable to their natural predators.
