Evaluating effort regulation in mixed fisheries: a Monte Carlo approach

12 This paper evaluates whether effort regulation could achieve the goal of pro13 tecting low-abundance species in mixed fisheries. We construct a two-species 14 bio-economic model and compare the stock abundance ratio in the end of the 15 fishing season with the ratio prior to the fishing. Fishers’ profit maximization 16 problem is governed by three key factors: (a) the overall efficiency of catching 17 different species (catchability), (b) the price of different species, and (c) their 18 ability to catch the favoured species separately from the less-favoured species 19 (separability). Using a Monte Carlo sampling of feasible parameters space, we 20 show that effort regulation has good chances (87% of the cases) of maintaining 21 the end stock ratio near equal levels (2 < stock ratio < 2) when the initial stock 22 ratio is equal. If the initial stock ratio is not equal, however, there is a high risk 23 (about 50% of the cases) that effort control increases differences in the rel24 ative species abundances, rather than diminishing them. The effects depend 25 on whether the key factors determining fishing profitability are counteracting 26 or reinforcing each other, and their relative strength. Our results warn against 27 placing too much faith on the ability of effort regulation to protect species at 28 low abundances from excessive exploitation. 29