Incorporating conservation zone effectiveness for protecting biodiversity in marine planning

Abstract

Establishing different types of conservation zones is becoming commonplace. However, spatial prioritization methods that can accommodate multiple zones are poorly understood in theory and application. It is typically assumed that management regulations across zones have differential levels of effectiveness ("zone effectiveness") for biodiversity protection, but the influence of zone effectiveness on achieving conservation targets has not yet been explored. Here, we consider the zone effectiveness of three zones: permanent closure, partial protection, and open, for planning for the protection of five different marine habitats in the Vatu-i-Ra Seascape, Fiji. We explore the impact of differential zone effectiveness on the location and costs of conservation priorities. We assume that permanent closure zones are fully effective at protecting all habitats, open zones do not contribute towards the conservation targets and partial protection zones lie between these two extremes. We use four different estimates for zone effectiveness and three different estimates for zone cost of the partial protection zone. To enhance the practical utility of the approach, we also explore how much of each traditional fishing ground can remain open for fishing while still achieving conservation targets. Our results show that all of the high priority areas for permanent closure zones would not be a high priority when the zone effectiveness of the partial protection zone is equal to that of permanent closure zones. When differential zone effectiveness and costs are considered, the resulting marine protected area network consequently increases in size, with more area allocated to permanent closure zones to meet conservation targets. By distributing the loss of fishing opportunity equitably among local communities, we find that 84-88% of each traditional fishing ground can be left open while still meeting conservation targets. Finally, we summarize the steps for developing marine zoning that accounts for zone effectiveness.

Figure 1. Study region and habitat maps of conservation features.

Our study region is the traditional fishing grounds of four provinces (i.e. Ra, Tailevu, Lomaiviti and Bua) along the coastline of the Vatu-i-Ra Seascape, Fiji. Conservation features were (1) fringing reefs, (2) non-fringing reefs, (3) mangroves, (4) intertidal areas, and (5) other benthic substrata less than 10 m in depth.

Figure 2. Result of classification of the solutions using multivariate normal mixture modeling.

We used the sub-model of VEV (volumes of all clusters as varying (V), shapes of all clusters as equal (E), and orientation of all clusters as varying (V)) to identify the number of clusters across all solutions between scenarios (n = 400) with the highest Bayesian Information Criterion (BIC). BIC is defined as twice the log likelihood in this method , unlike as for ordinal BIC.

Figure 3. The number of planning units selected as a permanent closure and partial protection zone in the best solution.

The allocation of selected planning units in the best solution (i.e. one solution that had the minimum score out of 100 runs) for each scenario. Scenarios used different zone effectiveness values (equal, highest, average, lowest) and relative zone costs. The numbers on the x-axis indicate the zone cost of the partial protection zone relative to the permanent closure zone (i.e. “75” means that the zone cost of partial protection zone is 75% of that of permanent closure zone).

Figure 4. The average opportunity costs of ten best solutions of scenarios.

Scenarios used different zone effectiveness values (1: equal, 2: highest, 3: average, 4: lowest zone effectiveness) with the different relative zone costs (75%, 50%, and 25%). The opportunity costs of fishing were obtained using the fishing pressure data and are the sum of the number of people living within 35 km of each planning unit.