Single Species, Biomass Based, Time Dependent Model for Investigating the Effects of Fishing on the Dynamics of Fish Biomass

摘要

When fishing (fishing mortality) increases in a given population, spawning stress mortality (senescent mortality) decreases. Thus the change of a population (biomass) is not a linear function of recruitment minus catch and a constant 'natural mortality'. Furthermore, fishing removes the older slower growing fish. Consequently, the mean growth rate of the remaining biomass increases. These two fishing dependent changes (called 'rejuvenation of population' by some earlier researchers) must be considered in biomass based fishery models because the removal of biomass by fishing is compensated by these changes to a considerable extent if recruitment remains constant. The effects of fishing on 'uncompensated' biomass dynamics, as well as biomass dynamics compensated for fishing (i.e., compensating for concomitant changes of growth rate and spawning stress mortality) are demonstrated with numerical examples for walleye pollock (Theragra chalcogramma) and yellowfin sole (Limanda aspera).