Patterns and prediction of population recovery in marine reserves

Marine reserves (no-take zones) are widely recommended as conservation and fishery management tools. One potential benefit of marine reserves is that they can reduce fishing mortality. This can lead to increases in the abunda nce of spawners, providing insurance against recruitment failure and mainta ining or enhancing yields in fished areas. This paper considers the factors that influence recovery following marine reserve protection, describes pat terns of recovery in numbers and biomass, and suggests how recovery rates c an be predicted. Population recovery is determined by initial population si ze, the intrinsic rate of population increase r, and the degree of compensa tion (increases in recruits per spawner as spawner abundance falls) or depe nsation (lower than expected recruitment at low abundance, Allee effect) in the spawner-recruit relationship. Within a reserve, theoretical recovery r ates are further modified by metapopulation structure and the success of in dividual recruitment events. Recovery also depends on the extent of reducti ons in fishing mortality (F) as determined by the relationship between patt erns of movement, migration, and density-dependent habitat use (buffer effe ct) in relation to the size, shape and location of the reserve. The effects of reductions in F on population abundance have been calculated using a va riety of models that incorporate transfer rates between the reserve and fis hed areas, fishing mortality outside the reserve and life history parameter s of the population. These models give useful indications of increases in p roduction and biomass (as yield per recruit and spawners per recruit respec tively) due to protection, but do not address recruitment. Many reserves ar e very small in relation to the geographical range of fish or invertebrate populations. In these reserves it may be impossible to distinguish recovery due to population growth from that due to redistribution. Mean rates of re covery can be predicted from r, but the methods are data intensive. This is ironic when marine reserves are often favoured for management or conservat ion in data-poor situations where conventional stock assessment is impossib le. In these data-poor situations, it may be possible to predict recovery r ates from very low population sizes by using maximum body size or age at ma turity as simple correlates of the intrinsic rate of natural increase.