Monitoring marine populations and communities: methods dealing with imperfect detectability

Abstract

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