Abstract
AbstractBottom trawl fisheries have significant effects on benthic habitats and communities, and these effects have been studied intensively in the last decades. Most of these studies have related the changes in benthic community composition to direct effect of trawl gears on benthos, through imposed mortality. This line of argumentation ignores the fact that benthic organisms themselves form a complex food web and that bottom trawling may trigger secondary effects through this food web. We studied the potential consequences of such food web effects using a model of benthic predators, filter feeders, deposit feeders and fish. Our analysis shows how inclusion of ecological interactions complicates the relationship between bottom trawling intensity and the state of the benthic community and causes a non‐linear and non‐monotonic response of the benthic community to trawling. This shows that indirect food web effects can fundamentally alter the response of a benthic ecosystem to bottom trawling, compared to the direct effects of mortality. In light of our results, we argue that indicators of fishing impact on benthos need to account for positive as well as negative effects of bottom trawling, in order to accurately quantify the impact. Our findings highlight that understanding the food web ecology of the benthic ecosystem is crucial for understanding and predicting the effects of trawling on the seafloor. Work that promotes such understanding of the food web ecology seems a more productive research strategy than conducting ever more empirical trawling effect measurements.
Highlights
It has long been acknowledged that bottom trawl fishing can strongly impact benthic habitats and the benthic ecosystem (Kaiser, 1998), something which was recently confirmed on a global scale (Hiddink et al, 2017)
The large variation in these studies is often attributed to inconsistencies in sampling design, data paucity or high background variation leading to low statistical power
The results presented here highlight how ecological interactions may affect the response of the benthic food web to bottom trawling
Summary
It has long been acknowledged that bottom trawl fishing can strongly impact benthic habitats and the benthic ecosystem (Kaiser, 1998), something which was recently confirmed on a global scale (Hiddink et al, 2017). We study how feedbacks through the food web can modify the effects of bottom trawling on long-term biomass abundance of functional groups in the benthos. Trawling mortality scaling coefficient for small and large fish resource carrying capacity on stable coexistence of the three benthic functional groups (Appendix S1C).
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