MEPS 586:41-55 (2018)  -  DOI:

Effects of chronic bottom trawling on soft-seafloor macrofauna in the Kattegat

Mattias Sköld1,*, Peter Göransson2, Patrik Jonsson1, Francois Bastardie3, Mats Blomqvist4, Stefan Agrenius5, Jan Geert Hiddink6, Hans C. Nilsson1, Valerio Bartolino

1Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, 453 30 Lysekil, Sweden
2PAG Environmental Research, 252 70 Råå, Sweden
3National Institute of Aquatic Resources, DTU Aqua Technical University of Denmark, 2920 Charlottenlund, Denmark
4Hafok AB, 179 61 Stenhamra, Sweden
5Department of Marine Sciences Kristineberg, University of Gothenburg, 451 78 Fiskebäckskil, Sweden
6School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey LL59 5AB, UK
*Corresponding author:

ABSTRACT: Impact studies of chronic bottom trawling aiming to reveal long-term effects on benthic organisms are often hampered by the lack of comparable untrawled conditions and the difficulty in assessing the spatial distribution of trawling intensity. We sampled soft-seafloor macrofauna over a precise trawling gradient in the Kattegat using hourly vessel monitoring systems and logbooks. The gradient included the establishment of a marine protected area (MPA), where trawling intensity declined sharply to zero. Our results show shifts in the macrofauna assemblage and non-linear responses, with decreases in the number and diversity of species at low to medium trawling intensities. The benthic community was dominated by burrowing brittle stars, of which one species, Amphiura chiajei, increased in abundance from low to medium trawling intensities. We interpret this positive response to increasing trawling intensities as a consequence of reduction in predation by benthivorous flatfish and Norway lobster Nephrops norvegicus, which are significant catches of the fishery. The response was supported by a corresponding trend towards lower abundance of the dominating brittle stars following enforcement of the MPA and presumably an increase in benthivore density and predation pressure within the MPA. We conclude that chronic bottom trawling reduces diversity and may boost the abundances of species resistant to bottom trawling. The results emphasize the need to consider food web effects when assessing the impact of bottom trawling.

KEY WORDS: Physical disturbance · Amphiura filiformis · Echinoderm · Otter trawling · Fishing impact · Food web · Benthic habitats · Nephrops norvegicus · Anti-predator defenses

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Cite this article as: Sköld M, Göransson P, Jonsson P, Bastardie F and others (2018) Effects of chronic bottom trawling on soft-seafloor macrofauna in the Kattegat. Mar Ecol Prog Ser 586:41-55.

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