Warming temperatures and smaller body sizes : synchronous changes in growth of North Sea fishes

Funded by Marine Scotland SciencePeer reviewedPostprin

Sediment mobilisation by bottom trawls : a model approach applied to the Dutch North Sea beam trawl fishery

Acknowledgements A. Lokker (Cooperatie Westvoorn), H. Klein-Woolthuis (HFK engineering), A. van Wijk (van Wijk, BV), M. Drijver and a number of individual skippers are gratefully acknowledged for providing information on gear dimensions. We tank Niels T. Hintzen for providing an updated data set with swept area ratios by grid cell for conventional tickler chain and chain mat beam trawl. Funding This study was funded by the European Maritime and Fisheries Fund (EMFF) and the Netherlands Ministry of Agriculture Nature and Food Quality (LNV) (Grand/Award Number: 1300021172), the Netherlands Ministry of Agriculture Nature and Food Quality (BO-code), the Belgian EMFF project “Benthisnationaal” and by the FP7-project BENTHIS (312088). The article does not necessarily reflect the views of the European Commission and does not anticipate the Commission’s future policy in this area.Peer reviewedPublisher PD

Indirect Effects of Bottom Fishing on the Productivity of Marine Fish

One quarter of marine fish production is caught with bottom trawls and dredges on continental shelves around the world. Towed bottom-fishing gears typically kill 20-50 per cent of the benthic invertebrates in their path, depending on gear type, substrate and vulnerability of particular taxa. Particularly vulnerable are epifaunal species, which stabilize the sediment and provide habitat for benthic invertebrates. To identify the habitats, fisheries or target species most likely to be affected, we review evidence of the indirect effects of bottom fishing on fish production. Recent studies have found differences in the diets of certain species in relation to bottom fishing intensity, thereby linking demersal fish to their benthic habitats at spatial scales of ~10 km. Bottom fishing affects diet composition and prey quality rather than the amount of prey consumed; scavenging of discarded by-catch makes only a small contribution to yearly food intake. Flatfish may benefit from light trawling levels on sandy seabeds, while higher-intensity trawling on more vulnerable habitats has a negative effect. Models suggest that reduction in the carrying capacity of habitats by bottom fishing could lead to lower equilibrium yield and a lower level of fishing mortality to obtain maximum yield. Trawling effort is patchily distributed - small fractions of fishing grounds are heavily fished, while large fractions are lightly fished or unfished. This patchiness, coupled with the foraging behaviour of demersal fish, may mitigate the indirect effects of bottom fishing on fish productivity. Current research attempts to scale up these localized effects to the population level

Quantifying habitat preference of bottom trawling gear

Continental shelves around the world are subject to intensive bottom trawling. Demersal fish assemblages inhabiting these shelves account for one-fourth of landed wild marine species. Increasing spatial claims for nature protection and wind farm energy suppresses, however, the area available to fisheries. In this marine spatial planning discussion, it is essential to understand what defines suitable fishing grounds for bottom trawlers. We developed a statistical methodology to study the habitat preference of a fishery, accounting for spatial correlation naturally present in fisheries data using high-resolution location data of fishing vessels and environmental variables. We focused on two types of beam trawls to target sole using mechanical or electrical stimulation. Although results indicated only subtle differences in habitat preference between the two gear types, a clear difference in spatial distribution of the two gears was predicted. We argue that this change is driven by both changes in habitat preference as well as a change in target species distribution. We discuss modelling of fisheries' habitat preference in light of marine spatial planning and as support in benthic impact assessments.</p

Socio-economic Impacts—Fisheries

Fishers and scientists have known for over 100 years that the status of fish stocks can be greatly influenced by prevailing climatic conditions. Based on historical sea surface temperature data, the North Sea has been identified as one of 20 ‘hot spots’ of climate change globally and projections for the next 100 years suggest that the region will continue to warm. The consequences of this rapid temperature rise are already being seen in shifts in species distribution and variability in stock recruitment. This chapter reviews current evidence for climate change effects on fisheries in the North Sea—one of the most important fishing grounds in the world—as well as available projections for North Sea fisheries in the future. Discussion focuses on biological, operational and wider market concerns, as well as on possible economic consequences. It is clear that fish communities and the fisheries that target them will be very different in 50 or 100 years’ time and that management and governance will need to adapt accordingly

North Sea demersal fisheries prefer specific benthic habitats

<p>Introduction The future protection of marine biodiversity through good conservation planning requires both the identification of key habitats with unique ecological characteristics and detailed knowledge of their human utilization through fisheries. Demersal fisheries are important disturbers of benthic habitats. They often have a heterogeneous spatial distribution, pressurizing particular habitats with high abundances of target species. For the North Sea, we quantified the commonness/rarity of habitats in relation to the environmental determinants of so-called fishing hotspots, to support better-informed conservation planning of benthic habitats in this intensively used continental shelf. Methods We first distinguished 9 main seascapes in the study area based on seabed morphology. Secondly, we determined average fishing intensity and fishing hotspots using VMS-data for the three dominant Dutch fisheries from 2008 to 2015: beam-trawlers targeting sole Solea solea (Beam-Sole), beam-trawlers targeting plaice Pleuronectes platessa (Beam-Plaice), and otter-trawlers targeting Norway lobster Nephrops norvegicus and demersal fish (Otter-Mix). Within the seascapes subjected to &gt;80% of the fishing activity, nineteen environmental factors (summarized by PCA) were used to ecologically characterize fishing hotspot locations using MaxEnt response modelling. Results We found that all three fisheries target highly specific, uncommon habitats. Beam-Sole fishers targeted warmer, shallow, dynamic, nearshore habitats, and within these specifically the depressions between sand ridges. Beam-Plaice fishers mainly targeted the exposed, non-muddy flanks of the Dogger Bank and similar large-scale elevations (50–75 km) where especially the ridges of smaller sand banks are used. Otter-Mix fisheries concentrated in areas with low bed shear stress, located in muddy, relatively deeper areas. Implications This study is the first to provide insight in benthic habitat types that are frequently targeted by fishers in the North Sea. We demonstrated unequal exploitation pressure between seabed habitats, with the majority of hotspots in the less common habitats. Our results hence contribute to a more effective, ecologically informed planning for the protection and monitoring of all seabed habitats and biodiversity of the North Sea.</p

Working Group on Electrical Trawling (WGELECTRA; outputs from 2021)

The Working Group on Electrical Trawling creates a platform for supra-national joint research projects on electro-trawling and scientific publications. The group also reviews all relevant studies on marine electrofishing and discusses the ongoing and upcoming research projects in the light of knowledge gaps. Research areas covered by the group included fishing tactics and dynamics, organisms and ecological impacts and selectivity of electro trawling. A study into the exploitation of local fishing grounds revealed that pulse trawlers and conventional tickler chain beam trawlers had similar tactics spending 10% of their tows searching for a fishing ground and spending 90% of their tows exploiting a fishing ground. In-situ field campaigns revealed a lower impact of pulse trawls on biogeochemical parameters compared to traditional beam trawl methods. Laboratory experiments found that while alternating or pulsed bipolar currents readily penetrated the sediment, biogeochemical effects appeared to be inhibited from occurring. The combined results concluded that the environmental impact of electricity from pulse trawls is relatively minor compared to the mechanical disturbances created from the same gears. Behavioral response thresholds for pulsed electric fields were determined in laboratory experiments for electroreceptive as well as non-electroreceptive fish species. Comparison of these thresholds to simulations of electric fields around commercial fishing gears suggest that electrical pulses are unlikely to substantially affect the investigated fish species outside the trawl track. A field study into direct mortality among fish and benthic organisms in the wake of pulse trawlers refuted claims that pulse trawling causes mass mortality among non-target species. A study into the selectivity of shrimp pulse trawling vs. traditional trawling concluded that that shrimp fishing using pulse gear does not result in higher amounts of undesired bycatches of small shrimp, fish and benthos when compared to the traditional shrimp beam trawl fisheries. The outline of a PhD project that started in 2021 into organism and ecological impacts of electrofishing for razor clams in Scottish shallow coastal habitats was presented and preliminary results were shared