Publication Abstract

Ogive characterisation in medium term stock projections

C.L. Needle, C.M. O'Brien and C.D. Darby

Under prevailing stock assessment methodologies, stochasticity is introduced into the simulation of future fish-stock population dynamics via random variation about a) a hypothesised recruitment model (possibly constrained to emulate the historical time-series of recruitment), and b) the initial population size. However, hindcast simulations suggest that the importance of appropriate characterisations of age-dependent measures of growth and reproductive potential may equal or exceed that of recruitment or starting numbers. This paper proposes two methodology modifications by which such concerns might be addressed: firstly, through vector autoregressive moving-average (VARMA) modelling of ma-turity and weights-at-age ogives in stock projections, and secondly by basing the requisite stock-recruitment models on a derived index of realised egg production rather than the traditional spawning-stock biomass. North Sea cod (Gadus morhua L.) and haddock (Melanogrammus aeglefinus L.) are used as test cases for the new method, and implications for the management of these and other stocks are discussed.

Reference:

C.L. Needle, C.M. O'Brien and C.D. Darby, 2001. Ogive characterisation in medium term stock projections. ICES CM 2001/V:19. 19pp.