MEPS prepress abstract  -  DOI:

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

Mattias Sköld*, Peter Göransson, Patrik Jonsson, Francois Bastardie, Mats Blomqvist, Stefan Agrenius, Jan Geert Hiddink, Hans C. Nilsson, Valerio Bartolino


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 to assess the spatial distribution of trawling intensity. We sampled soft sediment macrofauna over a precise trawling gradient in the Kattegat using hourly vessel monitoring systems and logbooks. The gradient accounted for the establishment of a marine protected area where trawling intensity declined sharply. Our results show shifts in the macrofauna assemblage and non-linear responses with decrease in number of species and diversity from low to medium trawling intensities. The benthic community was dominated by burrowing brittle stars, and one of the species, Amphiura chiajei, increased in abundance from low to medium trawling intensities. We interpret the positive response to increasing trawling intensities as a consequence of reduction in predation by benthivorous flatfish and Nephrops norvegicus that 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 benthivor 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.