Physical disturbance by towed bottom-tending fishing gear is ubiquitous on continental shelf seas. The ecological and physical consequences of this disturbance vary according to the environmental context in which they occur.
All human activities have an impact on the environment, and this is also true for fishing gear that is dragged over the seabed of our continental shelves. However, it is often difficult to assess whether such an impact "matters" to the environment.
This means that the significance of bottom-fishing impacts depends on the nature of the seabed habitats and the levels of natural seabed disturbance caused by waves and currents.
Ecological theory predicts that animals and plants living on and in the seabed are adapted to the naturally occurring levels of seabed disturbance that occur in their habitat. Shallow tide-swept and wave-impacted sandy habitats are characterized by animal communities that are well adapted to high rates of mortality and natural disturbance. As a consequence, these communities show greater resilience to accommodate additional sources of disturbance such as fishing disturbance. Conversely, deep and stable seabed habitats are often characterized by slow-growing, habitat-modifying species for which bottom fishing can have major and long-term impacts on biomass and diversity.
Whilst these relationships are relatively well understood, it remains a challenge to directly compare seabed disturbance caused by bottom-towed fishing gear with the natural disturbance of the seabed as different metrics are used to measure these difference sources of disturbance.
Diesing et al. describe a methodology that provides a basis for an objective and quantitative comparison of fishing and natural disturbance, based on data from the English part of the Greater North Sea.
The study identified areas where fishing disturbance is at a level beyond the range of natural background variability and also reveals where fishing disturbance is well within the limits of disturbance imposed by the natural environment.
The proposed methodology is particularly relevant when considered in the context of the need to evaluate 'Good Environmental Status' of sea-floor integrity (Descriptor 6 of the European Union's Marine Strategy Framework Directive).
To read the full article in the ICES Journal of Marine Science, please use the link provided.
