Optimal Age- and Gear-specific Harvesting Policies for North-East Arctic Cod

Florian K. Diekert, Dag Ø. Hjermann, Eric Nævdal and Nils Chr. Stenseth

Memo 16/2008

Last ned memo

We examine optimal harvest policies in a multi-cohort, multi-gear bioeconomic
model of North-East Arctic cod (Gadus morhua) which includes cannibalism and
contains broader ecosystem e ects. By controlling the selectivity of the di erent
shing equipment, we can partially target di erent age cohorts. We show that cur-
rent gear selectivity implies that the wrong sh are targeted. Optimization shifts
the exploitation pattern towards older and heavier sh. This increases the harvested
biomass while reducing the number of sh removed from the ocean. The result is
a much more robust and abundant cod stock with an age/size distribution closer
to the stocks natural state. We optimize the Net Present Value (NPV) generated
by the shery by letting e ort and selectivity be the control variables and nd that
NPV may be more than doubled, even when only gear selectivity or harvest e ort is
allowed to vary. (

Published June 20, 2014 9:57 AM - Last modified Jan. 24, 2019 11:43 AM