Section 4 provides discussion, while Section 5 presents concluding remarks and policy recommendations. The model used is developed by Flaaten and Mjølhus [14] and [15], based on the logistic growth model. This section presents the parts necessary for the current analysis. Important characteristics

of this model are that it ensures the same growth and yield potential pre- and post-MPA (denoted model A in Flaaten and Mjølhus [14] and [15]). The pre-MPA population is assumed to grow logistically and growth is given by equation(1) Ṡ=rS(1−S)−Y,where S is population size normalized by setting the carrying capacity equal to unity. Patchiness and ecosystem issues are disregarded and the habitat of the resource is a homogenous area, also equal to unity.

The intrinsic growth rate is r and Y is the harvest, selleck inhibitor assuming that harvest can be described by the www.selleckchem.com/products/MK-2206.html Schaefer catch function, Y=rES, where E is fishing effort, scaled such that the catchability coefficient equals the intrinsic growth rate. 1 This harvest function will be used later (see the last expression in Eq. (3)), but using stock density in the fishing zone rather than the total stock density. Pre-MPA S represents both the population size and density in a population distribution area of unit size. With the introduction of a reserve and a harvest area below, the population density in the harvest zone enters the harvest function instead of the total population. The carrying capacity as well as the habitat area is, as noted above, equal to unity in this modeling approach. When an

MPA is established it means that a fraction of the carrying capacity and the habitat is set aside for protection from fishing and other activities that could harm natural growth. This fraction is denoted m and is the size of the MPA relative to the habitat area. Introduction of an MPA of size m, a harvest zone (HZ) of size 1−m and assuming density dependent migration between the two areas alters the dynamics to equation(2) Ṡ1=r[S1(1−S1−S2)−γ(S1m−S21−m)] equation(3) Ṡ2=r[S2(1−S1−S2)+γ(S1m−S21−m)−ES21−m].S1 denotes population in area 1, the MPA, S2 the population in area 2, the HZ, E fishing effort and γ=σ/r, where σ >0 is the migration coefficient. Thus ADAM7 γ, the relative migration rate is the ratio of the migration coefficient to the intrinsic growth rate. Note that the population density in the HZ, and not the total population density, now enters the harvest function as shown in the last term in Eq. (3). The sustainable yield in the case of an MPA is equation(4) Y(S1,S2)=r(S1+S2)(1−(S1+S2)).Y(S1,S2)=r(S1+S2)(1−(S1+S2)).Thus sustainable yield is determined by the total stock, benefiting from the spillover to the harvest zone from the MPA. Unit price of harvest and cost of effort is assumed2 to be constant and the profit can thus be described by equation(5) π=pY–C,where p is the price per unit harvest and C is the total cost. Two different price and cost functions are used.