Development of sustainable management of sensitive habitats and species in the Kattegat (Sensitive habitats in the Kattegat) (39361)

Project Details

Description

The Kattegat is home to an intensive bottom trawl fishery for Norway lobsters (Nephrops norvegicus), and although the fishery on the target species is sustainable, intensive bottom trawling is known to impact sensitive benthic habitats and species significantly. In this project, we investigated how bottom trawling affects the fauna in the Kattegat by sampling selected stations with bottom grabs and trawls, by recording the fauna on the seabed with a towed video camera, and by counting and identifying the species attracted to baited video cameras. The sampling stations were mostly placed in the deeper muddy areas where Norway lobsters are abundant, but samples were also collected in shallower areas where sensitive species had been identified in previous investigations. Prior to sampling local fishermen were interviewed to identify potential Norway lobster grounds that were ‘de facto’ closed due to obstacles on the sea bed such as reefs and boulders, and side scan sonar was used to map the areas. Results from previous investigations and maps of fishing intensity were used to select the sampling locations, in order to ensure that a gradient from zero to intensive trawling were represented in the sampling design.

The four different sampling devices recorded different proportions of the fauna. The bottom grab samples mostly contained invertebrates that bury in the sediment (infauna) and smaller species of epifauna (fauna residing on the surface of the seabed). The towed video camera recordings featured larger epifaunal animals (megafauna) in areas with low fishing effort including species known to be sensitive to bottom trawling, such as sea pens (Virgularia mirabilis, Pennatula phosphorea), horse mussels (Modiolus modiolus), tube building crustaceans (Haploops spp.), and larger sea anemones (Pachycerianthus multiplicatus, Bolecera tuediae). The baited camera recorded species of scavenging invertebrates and fish that were attracted to the bait, including large amounts of hagfish (Myxine glutinosa) on the deeper intensely trawled stations, a species that was almost absent from the other gears deployed in the project. The trawl caught a variety of fish species not recorded in any of the other sampling devices as well as some of the larger mobile invertebrates. Given the differences in the species caught by the four sampling devices we conclude that adequate monitoring of the ecological impacts of bottom trawling requires a multitude of different sampling devices to fully describe the changes in benthic in- and epifauna, scavengers, and fish assemblage composition, as well as the effects of management measures, such as areal closures.

To quantify the impact of trawling on the bottom fauna we further analyzed the benthos data collected by the bottom grab. The scientific literature suggests that size and other biological traits are important covariates and these were included in the analysis together with fishing intensity and six environmental variables. The results showed that the larger animals in the grab samples were more affected by trawling than the smaller ones, and that all seven different benthic indicators tested responded significantly to trawling for this size group, but not for the smaller size group. Among the sensitive organisms recorded, Virgularia mirabilis and sea anemones were found on stations with low to intermediate trawling intensity. Pennatula phosphorea, Modiolus modiolus and Haploops spp. were found only at one station (not the same). Among the common species, bivalves and tube-building worms were the ones most heavily affected by trawling intensity. These findings show that trawling remains significant also when differences in the local physical and hydrodynamic conditions are accounted for.

Stakeholder meetings were held in order to engage the fishermen in the project and in discussions about how trawling impacts on sensitive species and habitats can be managed. The results of the project were visualized by an interactive model of the bottom of the Kattegat, showing where sensitive species and habitats were found, and where the Norway lobster fishery takes place. 

We conclude that areas closed to trawling primarily should be established where sensitive species and communities are found. Closing areas that are already heavily trawled cannot guarantee that these species and communities will establish themselves in the areas, and may re-allocate fishing effort from these areas to the areas where the sensitive species are currently found.

Partners
National Institute of Aquatic Resources, DTU AquaDanish Fisheries Production Organisation (DFPO), Denmark (coordinator)
Natural History Museum of Denmark (SNM)
World WiId Fund for Nature, Danish section (WWF DK) (external project consultant). 

Funding
The project is funded by the European Maritime and Fisheries Fund. 

Research area: Ecosystem based Marine Management
StatusFinished
Effective start/end date01/04/201631/12/2018

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