Monitoring marine populations and communities: methods dealing with imperfect detectability

Effective monitoring of populations and communities is a prerequisite for ecosystembased of marine areas. However, monitoring programs often neglect important of error and thus can lead to biased estimates, spurious conclusions and false management. One such source of error is ‘imperfect detectability’, i.e. the inability of investigators detect all individuals or all species in a surveyed area. Although there has been great effort to monitoring methods that account for imperfect detectability, the application of such methods the marine environment is not as apparent as in other systems. Plot sampling is by far the commonly applied method for biological monitoring in the marine environment, yet it largely detectability issues. However, distance sampling, mark-recapture methods, repeated-absence surveys for occupancy estimation, and removal methods do estimate detection and provide unbiased estimates of state variables. We review these methods and the tools for their application in studies on marine populations and communities, with the aim assisting marine biologists and managers to understand the limitations and pitfalls associated some approaches and to select the best available methods for their monitoring needs.