UW Aquatic & Fishery Sciences Quantitative Seminar
Elizabeth Moffitt
AFSC & UW
The design and implications of marine protected areas for mobile species
Abstract
Marine protected areas (MPAs) are being established globally as a tool for biodiversity conservation and fisheries management. Although MPAs are expected to benefit a wide range of species, most modeling efforts make the simplifying assumption that adults are sedentary. In order to assess the effects of adult and larval movement on persistence and yield within a network of MPAs, I incorporated adult movement within a home range into a spatially explicit population model. I then used this model to evaluate the use of size and spacing guidelines in MPA network design. Because the performance and utility of newly implemented MPAs will likely be judged based on the detection of MPA effects, I explored the question of under what time frame, exploitation level, and organism mobility relative to MPA size should we expect to detect MPA effects using a spatial, size, and age-structured population dynamic model. As expected, the capacity of a population to persist decreased with increasing home range size. For home ranging species, population persistence may be more predictable than previously anticipated from models based solely on larval dispersal, in part due to better knowledge of home range sizes. Including adult movement can change persistence results significantly from those of sedentary species; hence is an important consideration in MPA design. Size and spacing guidelines are a useful way to begin the MPA design process, but it is preferable to compare proposed MPA networks using spatially explicit population dynamics models that evaluate population persistence. Increasing MPA size and/or decreasing spacing was especially critical for species with extensive movement, and increasing MPA size was generally more effective than decreasing MPA spacing. The detection of MPA effects increased with exploitation rate and MPA age, and decreased with population mobility (particularly adult movement) relative to MPA size. Monitoring studies must be carefully designed with acknowledgement that spillover of adults and larvae across MPA boundaries may make detection of MPA effects difficult. Analyses of MPA effects can be greatly improved by empirical studies of MPA effects that also report movement of species relative to MPA size and a measure of the level of exploitation (beyond fished versus unfished).