The consequences of coastal offsets for fisheries

Biodiversity offsetting is increasingly used to mitigate biodiversity impacts from development, but the practice of offsetting rarely considers how to also mitigate losses of ecosystem services. Offset rules, such as how near an offset must be to an impact site, may help ensure biodiversity offsets also counterbalance losses of ecosystem services but this has not yet well understood. We explored how different rules for siting coastal offsets could change net impacts to a provisioning ecosystem service: fishery resources in Queensland, Australia. A spatially-explicit model incorporating supply, flow and demand of fishery resources was developed to simulate contributions of offset sites to commercial fisheries in Queensland, Australia. We simulated offsets for losses due to 63 real projects that damaged mangroves and 14 projects damaging seagrasses. We found that the percentage of species suffering net negative outcomes for the whole commercial fishery increased from about 68% when offsets were located close to impact sites to > 85% when there were no restrictions on offset location. All fisheries for seagrass offsets suffered net economic losses under both scenarios, but these were worse when offsets were not required to be near to impact sites. Offsetting outcomes varied substantially across species. Species with shorter maximum dispersal distance and higher dispersal decay parameters suffered greater net losses. Synthesis and applications. Our model quantified impacts of fishery habitat depletion and offsets on fishery resources and the approach can be applied to assess impacts of losses of fishery habitats globally. The findings suggest that to minimize losses of fishery resources caused by habitat depletion, offset policy should generally locate offset sites at the locations available for restoration that are nearest to impact sites, unless specific information about the relative contributions of sites to impacted fisheries is available to guide offset location.The data for traditional boat moorings located in existing seagrass habitats in Queensland is provided as potential seagrass offset sites in Queensland. Python script for the model