Passive fisheries of brown crab (Cancer pagurus) and European lobster (Homarus gammarus) in Dutch offshore wind farms : With reflections on its feasibility as a form of multi-use in offshore wind farms

Samenvatting

Passive fisheries of European lobster (Homarus gammarus) and brown crab (Cancer pagurus) have been proposed as viable opportunity to be combined with offshore windfarms (OWFs). However, it is currently unknown whether fisheries of European lobster and brown crab in OWFs in the North Sea are feasible from an ecological and economic point of view. As a desk study we describe three types of passive fishery techniques used for catching European lobster and brown crab (1. fykes; 2. gill nets and 3. pots and creels1) and their applicability to fisheries in North Sea OWFs. Based on the literature and interviews with fishermen (done inMay2021), pots and creels appear to be the most suitable method in OWFs. The main advantages of this type of fishery are limited by catch, less work involved (compared to gill nets) and the pots and creels are not prone to damage. The use of pots or creels to catch brown crab and lobster is mainly practised by fishermen in the United Kingdom and France. Three boats of Dutch fishermen target brown crab in the North Sea (northwest of Den Helder and above Texel to Terschelling, the so called Texelse Stenen) using pots with European lobster on the side (bonus catch). Lobster fisheries mainly occur in the Eastern Scheldt. In the subsequent parts all attention was given to the technique of pots. Although the actual density of both species in OWFs needs to be determined, based on German results, brown crab is currently the most promising target species when considering the population density and economic viability of passive fisheries in OWFs. Due to low population density trapping European lobster is considered a bonus for fishermen that target brown crab in the North Sea. The application of population enhancement strategies to increase harvest potential of lobster is investigated in a separate desk study. Information derived from interviews with Dutch crab fishermen coupled with knowledge on passive fisheries described in this desk study imply that the application of passive fisheries such as potting for brown crabs and European lobster is technically possible within OWFs and crab fishermen are willing to do so. The ecological feasibility however deserves further attention as well as the practicalities surrounding passive fisheries. The economic aspects are studied in a separate study. Besides population stock density uncertainties regarding safety, gear retrieval,insurance and liability are important factors of concern when it comes to the feasibility of passive fisheries in OWFs. In addition, it is important to realize that fishing in OWFs cannot be seen as an alternative to trawling. It is mainly a complementary form of small-scale fishing for a small group of fishermen, depending on the number and location of the OWFs being built. Recommendations point towards more insight in requirements for a combination of alternative fishing strategies (shorter strings, less spacing between pots or strings) designed to the specific lay-out of OWFs and exploring innovative design options of future OWFs that are more spacious or have additional features that allow for more multi-useopportunities in terms of low impact fisheries. Given the expected higher water currents, strings are laid out preferably parallel to the currents. Therefore it would be an option to have the infield-electricity cables of the OWF parallel to the currents, so that longer strings are possible. Also in fieldcables could be covered with rocks rather than to be buried in. The rocks would offer additional preferred habitat for brown crab and European lobster.