FISHERY BULLETIN: VOL 85, NO. 4 



1970 



1982 



Figure 1. — Annual catch of albacore by gear type. [Data from Majors and Miller. 

 1985. Summary of the 1984 North Pacific albacore fishery data. U.S. Natl. Mar. Fish. 

 Serv., Southwest Fish. Cent. Admin. Rep. LJ-85-14. 45 p.] 



albacore simulation model are the subject of this 

 report. 



THE MODEL 



We used a model that incorporates recruitment, 

 growth, migration, natural mortality, and har- 

 vest of albacore by the Japanese baitboat fleet, 

 the Japanese longline fleet, and the United States 

 surface fleet (primarily jig gear). Our approach 

 was to manipulate the effort of one fleet at a time 

 and note the effect on the catch of the other fleets. 



A full technical description of the model is 

 given by Kleiber and Baker^. We discretized fish 

 size into 5 cm length classes and the North Pacific 

 range of albacore into nine geographic zones (Fig. 

 3). The basic dynamics within a size class and 

 zone are described by the following differential 

 equation: 



dP.Jt) 

 dt 



- Gs-jPg-i^it. 



+ ^i^i 



P.^it) 



M 



Gs + ^ M-^ 



Ps^it) 



-2 



'S.Z.g 



2Kleiber, P., and B. Baker. 1987. The North Pacific alba- 

 core simulation model. U.S. Natl. Mar. Fish. Serv., Southwest 

 Fish. Cent., Admin. Rep. LJ-87-2, 38 p. 



where Cg^^ = Qs^ fzji^ Ps/t^ is the catch rate 

 (number per unit time) by size, zone, and gear. 

 The symbols are defined as follows: 



s — index for size class 



z — index for geographic zone 



z — index for zone adjacent to z 



g — index for gear type 



Ps,z^t ' — population (numbers) by size and zone at 

 time t 



the following being input parameters: 



Po,z^t^ — recruitment rate by zone at time t 



Gg — proportion growing out of size s per unit 



time 

 Go —always = 1 (so thatPQ ^(t) is recruitment 



rate) 

 M-zi—eo — coefficient of migration from zone Zj to 



zone 22 

 M — natural mortality 

 Qs,g — catchability by size and gear 

 fz^it) — effort by zone and gear at time t. 



INPUT PARAMETER VALUES 



Full details of how input parameters were esti- 

 mated are given by Kleiber and Baker (fn. 2). The 

 following is a summary. 



The most complete catch and effort data sets 

 that were available to us and that cover the three 



704 



