Optimizing removals to control a metapopulation: application to the yellowlegged herring gull (Larus cachinnans)

The standard one-site harvest maximization problem is extended to consider minimizing the cost associated with removing individuals from an annually i ncreasing 'nuisance' or 'pest' population exhibiting spatial structure (i.e . a metapopulation). We investigate the problem using a linear, determinist ic, multi-site matrix. A new approach for estimating the optimal harvest st rategy based on sensitivity analysis, rather than linear programming is pre sented. We show that the optimum stage class(es) to harvest can be determin ed from stage/site specific reproductive values (i.e. the components of the left eigenvector), weighted by stage/site specific harvest costs. The amou nt of harvest that should be directed at the determined stage(s) can be est imated from sensitivities. This method is illustrated for a Mediterranean g ull, the Yellow Legged Herring Gull (Larus cachinnans). Results obtained fr om the sensitivity analysis method (both a 'one-step' approximation and an iterative Newton-Raphson algorithm) are compared with linear programming so lutions. As expected, the iterative sensitivity method yields the same solu tions as linear programming, while the 'one-step' approximation underestima tes the level of harvest. Several constrained optimizations are investigate d to address spatial limitations and difficulties associated with age-deter mination. (C) 2001 Elsevier Science B.V. All rights reserved.