Assessing the effects of changes in exploitation pattern using length composition data (with notes on VPA and cohort analysis)
|Title||Assessing the effects of changes in exploitation pattern using length composition data (with notes on VPA and cohort analysis)|
|Year of Publication||1984|
|Series Title||FAO Fisheries Technical Paper|
|Document Number||Volume 256|
|Institution||Food and Agriculture Organization of the United Nations|
|ISBN Number||9251021813, 9789251021811|
Methods are described for using length composition data from commercial catches as a substitute for age-data in studying the dynamics of fish stocks. Particular attention is given to the extension of cohort and virtual population (VPA) techniques to length-data, and a brief description of the methods of application of VPA to age-data is also given. Given values for L infinity and M/K, length cohort analysis can be used to estimate the long term effect of a change in exploitation pattern. Alternatively, the results can be used to determine the current position on a yield isopleth diagram. Methods are also described for determining values of Z/K from the right hand part of a length composition, given a value for L infinity. If a value for M/K is also available, these results can also be used to determine the current position on a yield-isopleth diagram.