Implications of fish home range size and relocation for marine reserve function

Reserves are being used increasingly to conserve fish communities and popul ations under threat from overfishing, but little consideration has been giv en to how fish behavior might affect reserve function. This review examines the implications of how fish use space, in particular the occurrence and s ize of home ranges and the frequency and direction of home range relocation s. Examples are drawn primarily from the literature on coral reef fishes, b ut the principles apply to other habitats. Reserves can protect fish specie s only if individuals restrict their movements to a localized home range du ring at least part of the life cycle. home range sizes increase with body s ize. In small reserves, a significant proportion of fish whose home ranges are centered within the reserve can be exposed to fishing mortality because , their home ranges include non-reserve areas. Relocation of home ranges fo llowing initial settlement increases exposure to the fishery, especially if habitat selection is frequency-dependent. Distance, barriers, and costs of movement counter such redistribution. These considerations lead to predict ions that population density and mean fish size (1) will form gradients acr oss reserve boundaries with maxima in the center of the reserve and minima outside the reserve away from the boundary; (2) will increase rapidly in ne wly established reserves, only later providing 'spillover' to adjacent fish eries as density-dependent emigration begins to take effect; and (3) will b e higher in reserves that are larger and have higher area:edge ratios, more habitat types, natural barriers between reserve and non-reserve areas, and higher habitat quality inside than outside the reserve. (4) Species with l ow mobility and weak density-dependence of space use will show the greatest increase in reserves and the strongest benefit for population reproductive capacity, but those with intermediate levels of these traits will provide the greatest spillover benefit to nearby fisheries.