Abstract
The development of OWFs on the Dutch Continental Shelf can have adverse effects on the marine ecosystem. In recent years, many studies on this subject have been carried out, which provided highly valuable data and new insights. Still, at present many knowledge gaps exist which makes it difficult to draft a solid cumulative impact assessment for relevant species.
In this study, the Masterplan 1.0 (Deltares, 2010) was updated by assessing which knowledge gaps have been addressed over the last years and by making an inventory of new and remaining knowledge gaps. These knowledge gaps have been prioritized by both policy makers and scientific experts. Knowledge gaps concerning marine mammals, birds and bats are prioritized to be addressed on short term, described in more detail below.
Prioritized knowledge gaps:
Marine mammals
The knowledge gaps that have to be addressed with highest priority for marime mammals are (1) the percentage of surface area where effects on marine mammals occur in comparision to the dispersion area and (2) better threshold quantification in combination with more insight in actual behavioural response in the field during construction for both seals and marine mammals. Studies on these gaps will provide better quantified input parameters for the InterimCPOD model, which will contribute to more reliable impact assessments of construction of OWFs on marine mammals. From policy side it is explicitely noted that insights in the efficacy of mitigation measures should be acquired for the purpose of adaptive management.
Birds
The knowledge gaps that have to be addressed with highest priority for birds are (1) on the loss of habitat for (surface) farm avoiding bird species in relation with the total area, including species specification and abundances. and (2) insight in collision rates of birds in OWFs. Experts mainly focussed in the workshop discussion on the development of a system of collision quantification, where policy makers prioritized specifically the effects OWF configuration to minimize collision and habitat loss. Policy makers specifically prioritized insight in the efficacy of mitigation measures, by studying the effects of corridiors, open or closed configuration, small or large turbines, indirect lights, contrasting colors of rotor blades and foundation, and a cut-in speed at >4 Bft on both collision rate and habitat loss.
Bats
The knowledge gaps that have to be addressed with highest priority for bats are the behavioural characteristics of bats at sea. Knowledge of bats at sea is generally limited and should be acquired with high priority to be able to assess the impacts of OWFs on the bat population.
General
During the workshop, the need for international collaboration and data sharing was emphasized by both scientific experts and policy makers. This is not a knowledge gaps by itself, but needs to be facilitated in order to efficiently address the current existing knowledge gaps. Also, this will help in assess the (cumulative) impacts of OWFs on population level of species, as most species are not restricted to national boundaries.
Adaptive management
Knowledge gained in the coming years is extra valuable if it can be used for adaptive management. In order to get all necessary information in time, high priority studies should start and be executed as soon as possible. Adaptive management can only be applied when knowledge from research can be applied during the process, that is why timing is of utmost importance.
According to the time-schedule, the first construction phase is foreseen at the end of 2018, which implies that approx. 2.5 years are available to define and mature indicators for adaptive management. It is noted that applying adaptive management will be challenging; there will most likely be limited sufficiently accurate indicators available that can express the effects of construction and operational OWFs on population level on a short time scale.