Instantaneous separable VPA (ISVPA)

Abstract

The approach suggested is in the class of cohort methods; it is a new technique for processing catch-at-age data on species having short (within a year) periods of fishery. The method can also be regarded as an approximation to more general conditions when fishery varies continuously during the year. In many cases it enables a more complete extraction of information on exploited populations and fishery from the catch-at-age matrices, including the natural mortality coefficient and terminal fishing parameters, without using any auxiliary data (survey data, fishing effort series etc.). A number of numerical experiments using simulated data illustrate the methodology and demonstrate the merits of the suggested method.1997 International Council for the Exploration of the Sea

POPULATION DYNAMICS OF FLOUNDER (Platichthysflesus) IN ESTONIAN WATERS

“…The hypothesis of separability means that for all the years and age groups Fay= Sa XT,, where S, is proportional to the selectivity of fishery (an age effect), and 7, is proportional to the fishing effort (a year effect) (Darby & Flatman, 1994, Gassioukov, 1997Kizner & Vasilyev, 1997). In case of Simple Cohort analysis the fishing mortality is defined as follows: F, ,== LN(N 4 4 /Na,y) -M. (1)…”

Population Dynamics of the Main Pelagic Species Exploited in the Java Sea: Stock Evaluation

“…growth rate). Inserting a function replacing, ixp 1lltZ1 term for representing the effect oJ seasonal catches (Mertz & Myers, 1996)' but it seems to be an unclear approximation since the Droblem in quantification of that faclor has not 6een solved yet in this study Another solution has been proposed by regarding the model as an aDproximation to more general conditions when fiihery varies continuously during the year (Kizner & Vasilyev, 1997). These amended models, however, never consider the effect of migration, although the last one gives an option of zero catch that may be analogous to the undeterminable catch.…”