Abstract
Introduction
To meet the increasing need for renewable energy, the Dutch government has plans to use offshore wind farms (OWFs). With the resulting rapid upscaling of OWFs in the North Sea, there is increased stressors on nature and fisheries (with OWFs as closed areas for fisheries). Successful development and exploitation of OWFs require an integration that is inclusive of marine activities and foremost nature. Co-use is mentioned to meet these wishes and needs. Nature restoration projects are proposed as well as other types of co-use like passive fisheries with pots on crab and European lobster.
Artificial reefs and relevance for European lobster
In the Netherlands, artificial reefs are considered as an option for OWFs in their obligation to improve the marine biodiversity and thereby fortify the natural North Sea ecosystem. Artificial reefs could contribute in the restoration of formerly present hard substrates (like oyster banks and moreen deposits).
There is a need to improve knowledge on the use of artificial reefs in order to improve design and application. This includes: 1) gaining practical experience with nature enhancement options and 2) gain insight into the biodiversity development and functioning associated with such nature enhancement options. In that context, artificial pipe reef structures were deployed in the Dutch Borssele II OWF.
European lobster (Homarus gammarus, L) can be found on most hard substrates in the North Sea, like wrecks, anti-scouring, artificial reefs and (moreen) stone patches. They have a high site fidelity hiding in crevices. European lobster can be an important keystone species (i.e. acting as trophic system structurer) in local communities. With the deployment of artificial reefs, they are potentially an important species for the functioning of the food web, biomass and biodiversity. However, the use and relevance of such artificial structures by European lobster has not been investigated to date.
Passive fisheries
In addition to investigating the suitability of artificial reefs for European lobster, knowledge is needed on their behaviour and mobility in relation to catchability by baited pots and cages, i.e. for fisheries purpose. It is obligatory to place the baited pots and cages at considerable distances from hard substrate and crevices. The Dutch Ministerie van Binnenlandse Zaken defined a 250 m maintenance zone around monopile and anti-scouring. In order to evaluate the effectiveness of passive fisheries if animals inhabit the structures, it is essential to identify whether European lobsters have enough daily mobility to encounter bait scent at distances of ≥250 m. For example, a study on H. gammarus identified attraction distance of maximally 125m1, which could warrant against effective passive fisheries because of the 250 m maintenance zone. Such findings need to be explored further for European lobsters in the context of an OWF and obligatory distances to relevant objects as anti- scouring.
Knowledge need
The goal of the study was to develop more knowledge on the behaviour and habitat utilisation of individual translocated European lobster at the artificial reefs. More specifically, individual home ranges, movement characteristics and seasonal and diel activity patterns were monitored at fine spatial and temporal scales. These were further investigated in relation to substrate, sex and size of the European lobsters. In relation to fisheries, this research describes the natural behaviour of translocated European lobsters but without any influence of bait to estimate catchability.